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Constraints on primordial black holes as dark matter candidates from capture by neutron stars

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Abstract

We investigate constraints on primordial black holes (PBHs) as dark matter candidates that arise from their capture by neutron stars (NSs). If a PBH is captured by a NS, the star is accreted onto the PBH and gets destroyed in a very short time. Thus, mere observations of NSs put limits on the abundance of PBHs. High DM densities and low velocities are required to constrain the fraction of PBHs in DM. Such conditions may be realized in the cores of globular clusters if the latter are of a primordial origin. Assuming that cores of globular clusters possess the DM densities exceeding several hundred GeV/cm3^3 would imply that PBHs are excluded as comprising all of the dark matter in the mass range 3×1018gmBH1024g3\times 10^{18} \text{g} \lesssim m_\text{BH}\lesssim 10^{24} \text{g}. At the DM density of 2×1032\times 10^3 GeV/cm3^3 that has been found in simulations in the corresponding models, less than 5% of the DM may consist of PBH for these PBH masses.

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... The black hole capture rate can be calculated using the initial PBH mass (m PBH ), DM density and velocity dispersion (assuming a Maxwellian distribution). With the base Milky Way (MW) and UFD capture rates denoted as F MW 0 and F UFD 0 , one obtains [49] the full PBH-NS capture rates F = (Ω PBH /Ω DM )F MW 0 and F = (Ω PBH /Ω DM )F UFD 0 in the MW and UFD, respectively. The number of PBHs captured by a NS is F · t, where the time t is either t G or t UFD for the MW and the UFD, respectively. ...
... For our analysis we consider a typical NS with mass M N S = 1.5M and radius R N S = 10 km. The base NS-PBH capture rate F 0 is given by [49] ...
... Pulsar lifetimes in the presence of PBHs with a given number density can be estimated as t NS = 1/F + t loss + t con , where the first term describes the mean BH capture time, t loss is the time for the PBH to be brought within the NS once it is gravitationally captured, and t con is the time for the black hole to consume the NS. For a typical NS one finds [49] that t loss 4.1 × 10 4 (m PBH /10 22 g) −3/2 yr. The spherical accretion rate of NS matter onto the PBH is described by the Bondi equation ...
Preprint
We show that some or all of the inventory of r-process nucleosynthesis can be produced in interactions of primordial black holes (PBHs) with neutron stars (NSs) if PBHs with masses 1014M<MPBH<108M{10}^{-14}\,{\rm M}_\odot < {\rm M}_{\rm PBH} < {10}^{-8}\,{\rm M}_\odot make up a few percent or more of the dark matter. A PBH captured by a neutron star (NS) sinks to the center of the NS and consumes it from the inside. When this occurs in a rotating millisecond-period NS, the resulting spin-up ejects 0.10.5M\sim 0.1-0.5\,{\rm M}_{\odot} of relatively cold neutron-rich material. This ejection process and the accompanying decompression and decay of nuclear matter can produce electromagnetic transients, such as a kilonova-type afterglow and fast radio bursts. These transients are not accompanied by significant gravitational radiation or neutrinos, allowing such events to be differentiated from compact object mergers occurring within the distance sensitivity limits of gravitational wave observatories. The PBH-NS destruction scenario is consistent with pulsar and NS statistics, the dark matter content and spatial distributions in the Galaxy and Ultra Faint Dwarfs (UFD), as well as with the r-process content and evolution histories in these sites. Ejected matter is heated by beta decay, which leads to emission of positrons in an amount consistent with the observed 511-keV line from the Galactic Center.
... In this Letter we explore how novel GW signatures from binaries with atypical solar mass BHs can act as probes of tiny PBHs constituting DM. If a 10 −16 M PBH /M 10 −7 PBH interacts and is captured by a compact star (NS or WD), it will eventually consume the host [41]. For neutron stars, this scenario implies that corresponding binaries will be "transmuted" into binaries with a 1.2 − 2.5M BH instead of the NS, where the lower mass bound comes from observations [42] and theoretically could be far smaller [43,44]. ...
... Black hole capture -The capture rate of PBHs on NS can be estimated following [41] and depends on the PBH mass M PBH , DM density ρ DM and velocity dispersion v (assumed to follow Maxwellian distribution). The full capture rate is given by F = (Ω PBH /Ω DM )F 0 , where Ω PBH is the PBH contribution to the overall DM abundance Ω DM . ...
... where [41]. We assume that a typical NS is described by R NS = 10 km and M NS = 1.5M [45]. ...
Preprint
Primordial black holes (PBHs) interacting with compact stars in binaries lead to a new class of gravity wave signatures that we explore. A small 1016107M10^{-16} - 10^{-7} M_{\odot} PBH captured by a neutron star or a white dwarf will eventually consume the host. The resulting black hole will have a mass of only 0.52.5M\sim0.5-2.5 M_{\odot}, not expected from astrophysics. For a double neutron star binary system this leads to a transmutation into a black hole-neutron star binary, with a gravity wave signal detectable by the LIGO-VIRGO network. For a neutron star-white dwarf system this leads to a black hole-white dwarf binary, with a gravity wave signal detectable by LISA. Other systems, such as cataclysmic variable binaries, can also undergo transmutations. We describe gravity wave signals of the transmuted systems, stressing the differences and similarities with the original binaries. New correlating astrophysical phenomena, such as a double kilonova, can further help to distinguish these events. This setup evades constraints on solar mass PBHs and still allows for PBHs to constitute all of the dark matter. A lack of signal in future searches could constrain PBH parameter space.
... Note here that, to suppress the Higgs fluctuations, which are generated during the chaotic inflaton oscillating regime, a larger new inflation scale and e -folding number of the new inflation is desirable. If these parameters are quite large, PBHs with an interesting mass range could be generated [55][56][57][58][59][60][61][62]. The constraints from star formation [61] and neutron star capture [62] are shown in a gray shaded region with dotted and dashed lines. ...
... If these parameters are quite large, PBHs with an interesting mass range could be generated [55][56][57][58][59][60][61][62]. The constraints from star formation [61] and neutron star capture [62] are shown in a gray shaded region with dotted and dashed lines. This is because, as claimed in Ref. [63], the amount of DM inside globular clusters is assumed to be larger than the standard value and it seems to be questionable. ...
... As a result, even though the abundance of PBHs per logarithmic mass interval, Ω PBH (M ), is one order of magnitude smaller than that required to be DM, its total abundance can be comparable to the present DM density, Ω PBH, tot Ω c . Fig. 1 shows the present abundance of PBHs per logarithmic mass interval divided by that of DM, Ω PBH /Ω c , as a function of mass for one example of parameters which realize this interesting situation, together with observational constraints [55][56][57][58][59][60][61][62]. ...
Preprint
We revisit the compatibility between the chaotic inflation, which provides a natural solution to the initial condition problem, and the metastable electroweak vacuum, which is suggested by the results of LHC and the current mass measurements of top quark and Higgs boson. It is known that the chaotic inflation poses a threat to the stability of the electroweak vacuum because it easily generates large Higgs fluctuations during inflation or preheating and triggers the catastrophic vacuum decay. In this paper, we propose a simple cosmological solution in which the vacuum is stabilized during chaotic inflation, preheating and after that. This simple solution naturally predicts the formation of primordial black holes. We find interesting parameter regions where the present dark matter density is provided by them. Also, the thermal leptogenesis can be accommodated in our scenario.
... The current situation is shown in figure 1, assuming a monochromatic mass spectrum, appropriate for the very narrow mass distributions that we will consider later. 2 We emphasize that all the bounds come with various Fractional abundance of PBHs for the first example in table 1 (red curve) and observational bounds (for a monochromatic mass spectrum). The constraints are from measurements of the extragalactic gamma-ray background [17], femtolensing of gamma-ray bursts (Femto) [18], white dwarfs explosion (WD) [19], neutron star capture (NS) [20], microlensing from Subaru (HSC) [21] and EROS/MACHO [22], wide binaries observations (WB) [23], dynamical heating of ultra-faint dwarf galaxies (UFD) [24,25] (we have taken the solid black line in figure 4 of [24]), CMB measurements [26,27] and radio and X-rays observations [28]. The solid (dashed) line shows the constraints from HSC taking into account (neglecting) the effects of finite source size on the event rate of microlensing (see figure 25 in [21]). ...
... There is however a different mass window (around ∼ 10 −16.5 -10 −13 M ) for which a significant fraction of the DM (perhaps most or even all of it in the range ∼ 10 −14 − 10 −13 M ) might be due to PBHs. The limits that are currently available in the literature for these PBHs come from neutron star capture in globular clusters (NS) [20], white dwarfs explosions (WD) [19], femtolensing of gamma-ray bursts (Femto) [18] and microlensing from Subaru (HSC) [21]. Taken at face value, these bounds imply that monochromatic PBHs in this range can account at most for O(10)% of the DM content. ...
... Although a detailed discussion is outside the scope of our work, we would like to stress the importance of further observational and theoretical studies to clarify which are the possible windows where, given the current and possible future data, PBHs may be relevant as a DM candidate. At the PBH low-mass end (limited by Hawking evaporation) the available constraints on the literature come from: Subaru microlensing [21], hypothetical encounters between PBHs and neutron stars in globular clusters [20] or white dwarfs [19] and lensing of gamma-ray bursts by PBHs [18]. Some of these constraints are subject to significant uncertainties. ...
Preprint
We propose a model of inflation capable of generating a population of light black holes (about 101610^{-16} - 101410^{-14} solar masses) that might account for a significant fraction of the dark matter in the Universe. The effective potential of the model features an approximate inflection point arising from two-loop order logarithmic corrections in well-motivated and perturbative particle physics examples. This feature decelerates the inflaton before the end of inflation, enhancing the primordial spectrum of scalar fluctuations and triggering efficient black hole production with a peaked mass distribution. At larger field values, inflation occurs thanks to a generic small coupling between the inflaton and the curvature of spacetime. We compute accurately the peak mass and abundance of the primordial black holes using the Press-Schechter and Mukhanov-Sasaki formalisms, showing that the slow-roll approximation fails to reproduce the correct results by orders of magnitude. We study as well a qualitatively similar implementation of the idea, where the approximate inflection point is due to competing terms in a generic polynomial potential. In both models, requiring a significant part of the dark matter abundance to be in the form of black holes implies a small blue scalar tilt with a sizable negative running and a tensor spectrum that may be detected by the next-generation probes of the cosmic microwave background. We also comment on previous works on the topic.
... There is some uncertainty in this parameter, so we present our results arXiv:1705.05567v3 [astro-ph.CO] 9 Apr 2019 [8], the red region by femtolensing of gamma-ray bursts (FL) [40], the brown region by neutron star capture (NS) for different values of the dark matter density in the cores of globular clusters [41], the green region by white dwarf explosions (WD) [42], the blue, violet, yellow and purple regions by the microlensing results from Subaru (HSC) [43], Kepler (K) [44], EROS [45] and MACHO (M) [46], respectively. The dark blue, orange, red and green regions on the right are excluded by Planck data [36], survival of stars in Segue I (Seg I) [47] and Eridanus II (Eri II) [48], and the distribution of wide binaries (WB) [49], respectively. ...
... However, these limits are dependent on the DM density in the cores of globular clusters, which is very uncertain. Following Ref. [41], the neutron star capture constraint is presented for three values of this density (dashed and dot-dashed yellow lines). ...
... Most of the constraints shown in Fig. 1 rely on a single observable. For lensing this is the number of lensing events [40,43,45,46], for neutron star capture it is the age of neutron stars [41], and for white dwarfs and wide binaries it is their abundance [42,49]. However, some monochromatic constraints reported in the literature contain contributions from multiple observables. ...
Preprint
We revisit the cosmological and astrophysical constraints on the fraction of the dark matter in primordial black holes (PBHs) with an extended mass function. We consider a variety of mass functions, all of which are described by three parameters: a characteristic mass and width and a dark matter fraction. Various observations then impose constraints on the dark matter fraction as a function of the first two parameters. We show how these constraints relate to those for a monochromatic mass function, demonstrating that they usually become more stringent in the extended case than the monochromatic one. Considering only the well-established bounds, and neglecting the ones that depend on additional astrophysical assumptions, we find that there are three mass windows, around 4×1017M,4\times 10^{-17}M_\odot, 2×1014M2\times 10^{-14}M_\odot and 25100M25-100M_\odot, where PBHs can constitute all dark matter. However, if one includes all the bounds, PBHs can only constitute of order 10%10\% of the dark matter.
... In this Letter we discuss how PBHs interacting with compact stars can incite distinct gamma-ray burst (GRBs) and microquasar (MQs) sources, which can accelerate particles to high energies and contribute to the positron excess. Heuristically, if a small PBH with sublunar mass of 10 −16 M M PBH 10 −7 M is captured by a compact star [50], a white dwarf (WD) or a neutron star (NS), it will eventually consume the host and result in a stellar-mass BH. The system's energy, released on dynamical time-scales, is sufficient to power a short GRB. ...
... Black hole capture -A small PBH can become gravitationally captured by a NS or a WD if it loses sufficient energy through dynamical friction and accretion as it passes through the star. We briefly review the main capture ingredients, following [23,50]. The full capture rate is given by F = (Ω PBH /Ω DM )F 0 , where Ω PBH is the PBH contribution to the overall DM abundance Ω DM . ...
... We note that, in the mass ranges of 10 17 − 10 19 g and 10 20 − 10 23 g, PBHs can account for all of the dark matter. In the same mass range, one could use the stability of neutron stars to constrain PBHs if globular clusters contained 10 3 times the average dark matter density [50]. However, observations of globular clusters show no evidence of dark matter content in such systems, resulting in upper bounds three order of magnitude below the levels needed to allow for meaningful constraints [120,121]. ...
Preprint
We propose several novel scenarios how capture of small sublunar-mass primordial black holes (PBHs) by compact stars, white dwarfs or neutron stars, can lead to distinct short gamma-ray bursts (sGRBs) as well as microquasars (MQs). In addition to providing new signatures, relativistic jets from these systems will accelerate positrons to high energies. We find that if PBHs constitute a sizable fraction of DM, they can significantly contribute to the excess observed in the positron flux by the Pamela, the AMS-02 and the Fermi-LAT experiments. Our proposal combines the beneficial features of astrophysical sources and dark matter.
... Combining all existing experimental constraints [8], no PBHs with masses smaller than M < ∼ 10 −16 M ∼ 10 17 g should exist today in any relevant cosmological abundance. Above this limit, in the mass range 10 −16 < ∼ M/M < ∼ 10 5 , the lensing limits [10][11][12][13], various astrophysical and cosmic microwave background constraints [14][15][16][17][18][19] as well as the PBH merger rate estimates [20,21] imply that the PBHs cannot be the dominant DM component [22]. ...
... By using Eq. (14) we can then relate the maximal allowed fraction of DM in ECOs at given mass M to the maximal PBH DM fraction, [10], white dwarfs (WD) [15], neutron stars (NS) [14] and microlensing (HSC) [11]. For ECOs whose radiation is exponentially suppressed, the mass bounds are lowered by another 30 orders of magnitude. ...
... By using Eq. (14) we can then relate the maximal allowed fraction of DM in ECOs at given mass M to the maximal PBH DM fraction, [10], white dwarfs (WD) [15], neutron stars (NS) [14] and microlensing (HSC) [11]. For ECOs whose radiation is exponentially suppressed, the mass bounds are lowered by another 30 orders of magnitude. ...
Preprint
The radiation emitted by horizonless exotic compact objects (ECOs), such as wormholes, 2-2-holes, fuzzballs, gravastars, boson stars, collapsed polymers, superspinars etc., is expected to be strongly suppressed when compared to the radiation of black holes. If large primordial curvature fluctuations collapse into such objects instead of black holes, they do not evaporate or evaporate much slower than black holes and could thus constitute all of the dark matter with masses below M<1016M.M < 10^{-16}M_\odot. We reevaluate the relevant experimental constraints for light ECOs in this mass range and show that very large new parameter space down to ECO masses M10TeVM\sim 10\,{\rm TeV} opens up for light primordial dark matter. A new dedicated experimental program is needed to test this mass range of primordial dark matter.
... Set B includes dynamical constraints from Segue I [25], Eridanus II [26], and non-disruption of wide binaries [15]. Set C includes a constraint from white dwarf explosions [27], a constraint from neutron star capture [28] and a recently claimed constraint from SNe lensing in the LIGO window [29]. The constraints from evaporation and from Planck in A have been estimated differently in the literature, with important consequences for our analysis. ...
... The values of f max,all in table 1 demonstrate that the present observational status of PBH dark matter is strongly dependent on the constraints adopted. However, to rule out f PBH = 1, it is necessary to both take the more stringent constraintsĀ in place of A, and to include at least one of the constraints from set C: supernova microlensing [29], neutron star capture [28], and white dwarf explosions [27]. ...
... We note that this constraint is dominant in the LIGO window only when dynamical constraints from set B are neglected, so the addition of this constraint alone to set AB orĀB will have a small impact on f max,all . The constraint from neutron star capture is also subject to astrophysical uncertainties, since it is dependent on the dark matter density in the cores of galactic clusters [28]. We consider the relatively restrictive constraint obtained by taking ρ DM = 10 4 GeVcm −3 . ...
Preprint
The advent of gravitational wave astronomy has rekindled interest in primordial black holes (PBH) as a dark matter candidate. As there are many different observational probes of the PBH density across different masses, constraints on PBH models are dependent on the functional form of the PBH mass function. This complicates general statements about the mass functions allowed by current data, and, in particular, about the maximum total density of PBH. Numerical studies suggest that some forms of extended mass functions face tighter constraints than monochromatic mass functions, but they do not preclude the existence of a functional form for which constraints are relaxed. We use analytical arguments to show that the mass function which maximizes the fraction of the matter density in PBH subject to all constraints is a finite linear combination of monochromatic mass functions. We explicitly compute the maximum fraction of dark matter in PBH for different combinations of current constraints, allowing for total freedom of the mass function. Our framework elucidates the dependence of the maximum PBH density on the form of observational constraints, and we discuss the implications of current and future constraints for the viability of the PBH dark matter paradigm.
... The details of these processes are currently highly uncertain and, depending on the parameters of the simulation, the final outcome can be significantly different, see, e.g., refs. [93][94][95][96][97]. Despite this underlying uncertainty, it is commonly accepted that, if dark matter is retained inside GCs, it is more likely to be found in their cores [97][98][99]. ...
... [93][94][95][96][97]. Despite this underlying uncertainty, it is commonly accepted that, if dark matter is retained inside GCs, it is more likely to be found in their cores [97][98][99]. In particular, it has been shown that a dark matter component is expected in the core of GCs that formed at early times z ≳ 7 inside dark matter minihalos [97], even after accounting for the action of the tidal field of the host galaxy [88,100]. ...
... Despite this underlying uncertainty, it is commonly accepted that, if dark matter is retained inside GCs, it is more likely to be found in their cores [97][98][99]. In particular, it has been shown that a dark matter component is expected in the core of GCs that formed at early times z ≳ 7 inside dark matter minihalos [97], even after accounting for the action of the tidal field of the host galaxy [88,100]. If PBHs account for at least part of the dark matter and remain bounded to the clusters across their evolution, the possibility of finding them in the core is even more likely, due to the process of mass segregation, described in the next section. ...
Article
Full-text available
Primordial black holes still represent a viable candidate for a significant fraction, if not for the totality, of dark matter. If these compact objects have masses of order tens of solar masses, their coalescence can be observed by current and future ground-based gravitational wave detectors. Therefore, finding new gravitational wave signatures associated with this dark matter candidate can either lead to their detection or help constraining their abundance. In this work we consider the phenomenology of primordial black holes in dense environments, in particular globular clusters. We model the internal structure of globular clusters in a semi-analytical fashion, and we derive the expected merger rate. We show that, if primordial black holes are present in globular clusters, their contribution to the GW background can be comparable to other well-known channels, such as early- and late-time binaries, thus enhancing the detectability prospects of primordial black holes and demonstrating that this contribution needs to be taken into account.
... Once captured, the PBH is likely to lose more energy and ultimately be swallowed entirely, resulting in the PBH acting as an intruder in the host star. Due to their high densities, NSs turn out to be the most efficient at extracting energy from a PBH orbit, and are therefore the most likely to act like such a host and have a PBH embedded inside (see, e.g., [18][19][20][21][22][23] and references therein). Inside the NS, an "endoparasitic" PBH (borrowing the language of [24]) slowly spirals to the center of the NS, accretes stellar material, and ultimately induces dynamical collapse of the host star (see [24][25][26][27] for numerical simulations). ...
... Event rates for collisions between PBHs and NSs are estimated to be small (see, e.g., [17,19,28,29,34], as well as Section I of the Supplemental Material in [33]), so that the detection of such a GW signal will most likely be possible only with more sensitive GW detectors than those currently available. However, these estimates depend on a number of assumptions, and the event rates could be more favorable in special environments (e.g. ...
... Only 95% limits are provided in [6], and thus the left panel omits symbols (and colors) for a higher credibility limit. by a number of different authors (see, e.g., [18][19][20][21][22][23]), this process is most likely to happen for NSs. Once inside the NS, the motion of the PBH is governed by both dynamical and secular processes. ...
Preprint
Lacking terrestrial experimental data, our best constraints on the behavior of matter at high densities up to and above nuclear density arise from observations of neutron stars. Current constraints include those based on measurements of stellar masses, radii, and tidal deformabilities. Here we explore how orbits of primordial black holes - should they exist - inside neutron stars could provide complementary constraints on the nuclear equation of state (EOS). Specifically, we consider a sample of candidate EOSs, construct neutron star models for these EOSs, and compute orbits of primordial black holes inside these stars. We discuss how the pericenter advance of eccentric orbits, i.e. orbital precession, results in beat phenomena in the emitted gravitational wave signal. Observing this beat frequency could constrain the nuclear EOS and break possible degeneracies arising from other constraints, as well as provide information about the host star.
... Most of other proposals in the asteroid mass range turn around using stars as PBH detectors. They are based either on the capture of PBHs by stars with the subsequent star destruction [8,9,10,11,12], or on ignition of nuclear reactions in white dwarfs by a traversing PBH [13]. An overview of these proposals can be found in Ref. [14]. ...
... More accurately, one has to average the energy loss over the PBH impact parameter. If one assumes for simplicity the uniform distribution of the PBH trajectories in the plane perpendicular to the PBH velocity we get, in agreement with eq.(2) of Ref. [8] ...
... The calculation of the dynamical friction that takes into account both effects can be found in the Appendix of Ref. [8] where the contribution of the force due to the direct accretion was also included. The resulting energy loss, averaged over different impact parameters of PBH trajectories passing through the star, was found to be loss = ...
Preprint
Full-text available
Primordial black holes (PBHs) are an attractive dark matter candidate, particularly if they can explain the totality of it. At PBH masses below 1017\sim 10^{17}g and above 1023\sim 10^{23}g this possibility is excluded from the variety of arguments and with different confidence. The range in between, often referred to as the "asteroid mass window", currently remains unconstrained. The most promising, in our view, way to probe this mass range is to use stars as the PBH detectors. If a star captures even a single PBH it starts being accreted onto it and eventually gets destroyed -- converted into a sub-solar mass black hole. This process may have a variety of signatures form a mere star disappearance to supernova-type explosions of a new kind. The viability of this approach depends crucially on the probability of PBH capture by stars. In this chapter we summarize the existing capture mechanisms and discuss their implications for constraining the abundance of (or perhaps discovering) PBHs in the asteroid mass window.
... A noticeable exception is the possibility that PBH form stable relics with Planck-like mass [18] after their evaporation. Very stringent constraints have been set on their abundances, from various observations: if m PBH 7×10 12 kg, the gamma-ray radiation due to PBH evaporation should have been detected by EGRET and FERMI [17]; within the range 5 × 10 14 − 10 17 kg, they should have been detected by FERMI through the gravitational femto-lensing of gamma-ray bursts [19]; for 10 15 < m PBH < 10 21 kg PBHs should have destroyed neutron stars in globular clusters [20]; the absence of microlensing events of stars in the Magellanic clouds exclude large abundances of PBHs within the range 10 23 − 10 31 kg [21][22][23], although such * clesse@physik.rwth-aachen.de † juan.garciabellido@uam.es ...
... The capture rate can be compared to the direct merging rate τ merg PBH , which was derived in the Newtonian approximation in Refs. [20,49] in the context of WIMPneutron star and PBH-neutron star collisions respectively, assuming that two PBH merge if the closest distance between them is smaller than the Schwarzschild radius R PBH = 2Gm PBH /c 2 . This rate is given by ...
Preprint
The recent detection by Advanced LIGO of gravitational waves (GW) from the merging of a binary black hole system sets new limits on the merging rates of massive primordial black holes (PBH) that could be a significant fraction or even the totality of the dark matter in the Universe. aLIGO opens the way to the determination of the distribution and clustering of such massive PBH. If PBH clusters have a similar density to the one observed in ultra-faint dwarf galaxies, we find merging rates comparable to aLIGO expectations. Massive PBH dark matter predicts the existence of thousands of those dwarf galaxies where star formation is unlikely because of gas accretion onto PBH, which would possibly provide a solution to the missing satellite and too-big-to-fail problems. Finally, we study the possibility of using aLIGO and future GW antennas to measure the abundance and mass distribution of PBH in the range [5 - 200] Msun to 10\% accuracy.
... The model of macroscopic DM.-The discussion of macroscopic-size dark matter was traditionally oriented towards the massive compact halo objets (MACHOs) and primordial black holes. The range of suggested masses for these candidates starts from rather large values, M > 10 14 g [4,5]. This mass range influenced early discussions on a possible use of space-based gravitational-wave inteferometers in search for dark matter [6,7]. ...
... The ability of LIGO and LISA to place constraints on g and λ depends on the mass of DM object; in both cases, the smallest masses considered (0.1 kg for LIGO, 10 9 kg for LISA) allow for the most sensitivity to {g, λ} parameter space. If we choose δ SM close to the existing bounds, and δ DM to saturate (5), then the rate of loud encounters can exceed O(10) per year. ...
Preprint
While global cosmological and local galactic abundance of dark matter is well established, its identity, physical size and composition remain a mystery. In this paper, we analyze an important question of dark matter detectability through its gravitational interaction, using current and next generation gravitational-wave observatories to look for macroscopic (kilogram-scale or larger) objects. Keeping the size of the dark matter objects to be smaller than the physical dimensions of the detectors, and keeping their mass as free parameters, we derive the expected event rates. For favorable choice of mass, we find that dark matter interactions could be detected in space-based detectors such as LISA at a rate of one per ten years. We then assume the existence of an additional Yukawa force between dark matter and regular matter. By choosing the range of the force to be comparable to the size of the detectors, we derive the levels of sensitivity to such a new force, which exceeds the sensitivity of other probes in a wide range of parameters. For sufficiently large Yukawa coupling strength, the rate of dark matter events can then exceed 10 per year for both ground- and space-based detectors. Thus, gravitational-wave observatories can make an important contribution to a global effort of searching for non-gravitational interactions of dark matter.
... The constraints for a monochromatic PBH mass function are shown in Fig. 3. For the evaporation constraint we take = 0.2 [63] where gives the slope of the extragalactic γ-ray background; for the neutron-star capture constraint, we assume a DM density ρ DM = 2×10 3 GeVcm −3 in the core of globular clusters [64]; for the Planck accretion constraint we show the most conservative bound [65]. PBHs with M < M * ≡ 4 × 10 14 g = 10 −18.6 M (i.e. ...
... The strongest constraints on their abun- The lines show the different constraint for a monochromatic PBH mass function. The purple region on the left is excluded by evaporation [63], the red region by femto-lensing of gamma-ray bursts [69], the brown region by neutron-star capture [64], the green region by white dwarf explosions [70], the blue, yellow and purple regions by microlensing results from Subaru [71], EROS [72], and MACHO [73] respectively, and the dark blue region by Planck [65]. The regions to the right of the dashed lines are excluded by survival of a stars in Segue I [74] and Eridanus II [75], and distribution of wide binaries [76]. ...
Preprint
We study production of primordial black holes (PBHs) during an early matter-dominated phase. As a source of perturbations, we consider either the inflaton field with a running spectral index or a spectator field that has a blue spectrum and thus provides a significant contribution to the PBH production at small scales. First, we identify the region of the parameter space where a significant fraction of the observed dark matter can be produced, taking into account all current PBH constraints. Then, we present constraints on the amplitude and spectral index of the spectator field as a function of the reheating temperature. We also derive constraints on the running of the inflaton spectral index, dn/dlnk0.002{\rm d}n/{\rm d}{\rm ln}k \lesssim -0.002, which are comparable to those from the Planck satellite for a scenario where the spectator field is absent.
... Axions, produced within main-sequence and neutron stars, could alter their structure and emission properties [43][44][45]. Moreover, primordial black holes, a potential dark matter candidate, could be captured by neutron stars, resulting in mergers detectable through gravitational wave signals [46]. These potential interactions underscore the importance of continued research and observation to validate these theoretical predictions and shed light on the elusive nature of dark matter. ...
... The solutions provide the discrete eigenvalues ω 2 n and can be ordered as ω 2 0 < ω 2 1 < ... < ω 2 n , where n is the number of nodes for a star of a given mass and radius. Finally, once the spectrum is known, the so called large frequency separation may be computed ∆ν n = ν n+1 − ν n , n = 0, 1, 2, 3, ... (46) or in other words the difference between consecutive modes, which is widely used in Asteroseismology to learn about star properties, inner structure and composition. ...
Preprint
We investigate the structure and radial oscillations of anisotropic compact stars composed of dark energy, using the vanishing complexity factor formalism within general relativity. This novel approach establishes a direct link between the energy density and anisotropic factor, providing a robust framework for studying these exotic stellar objects. Employing an Extended Chaplygin Gas equation of state, we numerically compute interior solutions for both isotropic and anisotropic stars, revealing distinct differences in their properties. Additionally, we examine the oscillation modes and frequencies of these stars, highlighting the impact of anisotropy on their pulsational behavior. Our results reveal distinct differences in the stellar properties, such as the metric potentials, pressure, speed of sound, and relativistic adiabatic index, between the two cases. Furthermore, we calculate the large frequency separation for the fundamental and first excited modes, offering insights relevant for future asteroseismology studies. Our findings shed light on the complex interplay of gravity, matter, and anisotropy in compact stars, providing a new perspective on dark energy's role in their structure and dynamics.
... The details of these processes are currently highly uncertain and, depending on the parameters of the simulation, the final outcome can be significantly different, see, e.g., refs. [88][89][90][91][92]. Despite this underlying uncertainty, it is commonly accepted that, if dark matter is retained inside GCs, it is more likely to be found in their cores [92][93][94]. ...
... [88][89][90][91][92]. Despite this underlying uncertainty, it is commonly accepted that, if dark matter is retained inside GCs, it is more likely to be found in their cores [92][93][94]. If PBHs account for at least part of the dark matter and remain bounded to the clusters across their evolution, the possibility of finding them in the core is even more likely, due to the process of mass segregation, described in the next section. ...
Preprint
Full-text available
Primordial black holes still represent a viable candidate for a significant fraction, if not for the totality, of dark matter. If these compact objects have masses of order tens of solar masses, their coalescence can be observed by current and future ground-based gravitational wave detectors. Therefore, finding new gravitational wave signatures associated with this dark matter candidate can either lead to their detection or help constraining their abundance. In this work we consider the phenomenology of primordial black holes in dense environments, in particular globular clusters. We model the internal structure of globular clusters in a semi-analytical fashion, and we derive the expected merger rate. We show that, if primordial black holes are present in globular clusters, their contribution to the GW background can be comparable to other well-known channels, such as early- and late-time binaries, thus enhancing the detectability prospects of primordial black holes and demonstrating that this contribution needs to be taken into account.
... Nevertheless, we expect that these constraints should not change when moving from the Schwarzschild PBH framework to the PRBHs considered in this work. Indeed, with all other quantities being fixed (mass of source, relative 7 Potential exceptions to this mass range for dynamical constraints are those from capture of PBHs by white dwarfs or neutron stars at the centres of globular clusters [370][371][372], or from supernovae explosions resulting from transit of a PBH through a white dwarf [373]. However, these limits are highly disputed because of uncertainties in the dark matter density in globular clusters [374,375], or based on the results of hydrodynamical simulations [376]. ...
Article
Full-text available
Primordial black holes (PBHs) are usually assumed to be described by the Schwarzschild or Kerr metrics, which however feature unwelcome singularities. We study the possibility that PBHs are nonsingular objects, considering three phenomenological, regular tr (time-radial)-symmetric space-times (including the well-known Bardeen and Hayward ones), featuring either de Sitter or Minkowski cores. We characterize the evaporation of these PBHs and constrain their abundance from 𝛾-ray observations. For all three metrics we find that constraints on 𝑓pbh, the fraction of dark matter (DM) in the form of PBHs, weaken with respect to the Schwarzschild limits, because of modifications to the PBH temperature and graybody factors. This moves the lower edge of the asteroid mass window down by potentially an order of magnitude or more, leading to a much larger region of parameter space where PBHs can make up all the DM. A companion paper is devoted to non-tr-symmetric metrics, including loop quantum gravity-inspired ones. Our work provides a proof-of-principle for the interface between the DM and singularity problems being a promising arena with a rich phenomenology.
... The Bondi accretion of the NS onto the PBH leads to the destruction of the NS in a short time, meaning that observations of NSs can impose constraints on the abundance of PBHs in the mass range of 10 20 -10 23 g (F. Capela et al. 2013aCapela et al. , 2013b. The effects of NS rotation and the viscosity of nuclear matter on the accretion and spin evolution of PBHs were examined in C. Kouvaris & P. Tinyakov (2014). ...
Article
Full-text available
Gravitational waves (GWs) from primordial black holes (PBHs) inspiraling within neutron stars (NSs)—should they exist—are detectable by ground-based detectors and offer a unique insight into the internal structure of NSs. To provide accurate templates for GW searches, we solve Einstein’s equations within NSs and calculate the orbital motion of the captured PBH by considering dynamical friction, accretion, and gravitational radiation. Equipped with precise GW waveforms for PBHs inspiraling inside NSs, we find that the Einstein Telescope can differentiate between various equations of state for NSs. As PBHs inspiral deeper into NSs, the GW frequency rises near the surface, then decreases to a constant value deeper within NSs. The distinctive characteristics of GW frequency serve as the smoking gun for GW signals emitted by PBHs inspiraling inside NSs and can be used to probe the nuclear matter in the crust and core of NSs.
... The PBHs with mass around 10 15 g would be evaporating today and the extragalactic γ-rays provides a stringent constraint on them [13], i.e. f pbh < ∼ 2 × 10 −8 (M pbh /M * ) 3.2 for M pbh > M * = 5 × 10 14 g. Since the neutron star gets destroyed in a very short time due to the accretion onto PBH once a PBH is captured by it, this effect gives a constraint on the abundance of PBHs (f pbh < 0.05 for 3 × 10 18 g < ∼ M pbh < ∼ 10 24 g) [14]. The observations of stars in the Magellanic Clouds for microlensing events caused by MACHO (massive astrophysical compact halo object) are also used to test the hypothesis that MACHO could be a major component of the dark matter halo of the Milky Way galaxy, and,unfortunately, both EROS-2 (Eath Resources Observation Satellite) and OGLE (Optical Gravitational Lensing Experiment) rule out MACHOs as the majority of Galactic dark matter over the range 0.6 × 10 −7 M < M pbh < 15M : f pbh < 0.04 for 10 −3 M < ∼ M pbh < ∼ 10 −1 M and f pbh < 0.1 for [15]; f pbh < ∼ 0.06 for 0.1M < ∼ M pbh < ∼ 0.4M and f pbh < ∼ 0.2 for 0.4M < ∼ M pbh < ∼ 15M in [16,17]. ...
Preprint
We use Planck data released in 2015 to constrain the abundance of primordial black holes (PBHs) in dark matter in two different reionization models (one is the instantaneous reionization and the other is the asymmetric reionization), and significantly improve the upper limits on the abundance of PBHs from WMAP 3-year data by around two orders of magnitude. Furthermore, these new limits imply that the event rates of mergers of PBH binaries (Gpc3^{-3} yr1^{-1}) are less than 0.002 for Mpbh=30MM_\text{pbh}=30M_\odot, 5 for Mpbh=10MM_\text{pbh}=10M_\odot and 2000 for Mpbh=2MM_\text{pbh}=2M_\odot at 95%95\% confidence level (C.L.), and thus GW150914 seems very unlikely produced by the merger of a PBH binary.
... As a consequence, the set of constraints coming from a variety of observables is broad too. Starting from the lower allowed mass, constraints come from γ-rays derived from black holes evaporation [11], quantum gravity [12], γ-rays femtolensing [13], white-dwarf explosions [14], neutron-star capture [15], microlensing of stars [16][17][18][19][20] and quasars [21], stellar distribution in ultra-faint dwarf galaxies [22], X-ray and radio emission [23], wide-binaries disruption [24], dynamical friction [25], quasars millilensing [26], large-scale structure [27] and accretion effects [28][29][30][31]; given the strong interest in the model, there have been recently suggestions for obtaining constraints from e.g. the cross-correlation of gravitational waves with galaxy maps [32,33], eccentricity of the binary orbits [34], fast radio bursts lensing [35], the black hole mass function [36,37] and merger rates [38]. ...
Preprint
The model in which Primordial Black Holes (PBHs) constitute a non-negligible fraction of the dark matter has (re)gained popularity after the first detections of binary black hole mergers. Most of the observational constraints to date have been derived assuming a single mass for all the PBHs, although some more recent works tried to generalize constraints to the case of extended mass functions. Here we derive a general methodology to obtain constraints for any PBH Extended Mass Distribution (EMD) and any observables in the desired mass range. Starting from those obtained for a monochromatic distribution, we convert them into constraints for EMDs by using an equivalent, effective mass MeqM_{\rm eq} that depends on the specific observable. We highlight how limits of validity of the PBH modelling affect the EMD parameter space. Finally, we present converted constraints on the total abundance of PBH from microlensing, stellar distribution in ultra-faint dwarf galaxies and CMB accretion for Lognormal and Power Law mass distributions, finding that EMD constraints are generally stronger than monochromatic ones.
... The hypothesis that DM is constituted by a relic abundance of PBH is severely constrained by astrophysical and cosmological observations. The strictest bounds arise from the black hole evaporation [38,74,75], femtolensing [76], microlensing [77][78][79][80], energy injection during the CMB era by black hole accretion [81][82][83][84], neutron star capture [85], white dwarf explosions [86], survival of stars in dwarf galaxies [87,88], distribution of wide star binaries [89] etc. (for a detailed description see [37][38][39]). We remark, however, that many of these constraints rely on different assumptions and involve uncertainties, in a way that not all of them should be taken on equal footing. ...
Preprint
Within the framework of scalar-tensor theories, we study the conditions that allow single field inflation dynamics on small cosmological scales to significantly differ from that of the large scales probed by the observations of cosmic microwave background. The resulting single field double inflation scenario is characterised by two consequent inflation eras, usually separated by a period where the slow-roll approximation fails. At large field values the dynamics of the inflaton is dominated by the interplay between its non-minimal coupling to gravity and the radiative corrections to the inflaton self-coupling. For small field values the potential is, instead, dominated by a polynomial that results in a hilltop inflation. Without relying on the slow-roll approximation, which is invalidated by the appearance of the intermediate stage, we propose a concrete model that matches the current measurements of inflationary observables and employs the freedom granted by the framework on small cosmological scales to give rise to a sizeable population of primordial black holes generated by large curvature fluctuations. We find that these features generally require a potential with a local minimum. We show that the associated primordial black hole mass function is only approximately lognormal.
... The HSC constraints reported in Ref. [63] do not apply below 10 23 g because the micro-lensing magnification is strongly suppressed when the Schwarzschild radius of the black hole becomes smaller than the wavelength of light [66,67]. In the same mass range, one could use the stability of neutron stars to constrain PBHs if globular clusters contained 10 3 times the average dark matter density [69]. However, observations of globular clusters show no evidence of dark matter content in such systems, resulting in upper bounds three order of magnitude below the levels needed to allow for meaningful constraints [70,71]. ...
Preprint
We show that fragmentation of the inflaton into long-lived spatially localized oscillon configurations can lead to copious production of black holes. In a single-field inflation model primordial black holes of sublunar mass can form, and they can account for all of the dark matter. We also explore the possibility that solar-mass primordial black holes, particularly relevant for gravitational wave astronomy, are produced from the same mechanism.
... Since the size of the Milky Way halo is much larger, it is important to constrain the abundance of SULCOs that reside at distance > 4 kpc as well. The neutron-star capture constraint for a mass range of 10 −15 M ⊙ ≤ M ≤ 10 −9 M ⊙ [7] depends on the assumption that the PBHs reside in globular clusters, thus the limit is uncertain [11]. ...
Preprint
By monitoring a large number of stars in the Local Group galaxies, we can detect nanolensing events by sub-lunar mass compact objects (SULCOs) such as primordial black holes (PBHs) and rogue (free-floating) dwarf planets in the Milky Way halo. In contarst to microlensing by stellar-mass objects, the finite-source size effect becomes important and the lensing time duration becomes shorter (1014s\sim 10^{1-4}\,\textrm{s}). Using stars with V<26V<26 in M33 as sources, for one-night observation, we would be able to detect 103410^{3-4} nanolensing events caused by SULCOs in the Milky Way halo with a mass of 109M10^{-9}M_{\odot} to 107M10^{-7}M_{\odot} for sources with S/N>5>5 if SULCOs constitute all the dark matter components. Moreover, we expect 101210^{1-2} events in which bright blue stars with S/N>100>100 are weakly amplified due to lensing by SULCOs with a mass range of 1011M10^{-11}M_{\odot} to 109M10^{-9}M_{\odot}. Thus the method would open a new window on SULCOs in the Milky Way halo that would otherwise not be observable.
... In Refs. [29,30], it is claimed that neutron stars (NSs) in the globular clusters may capture PBHs which destroys NSs immediately. The existence of NSs in the globular clusters puts constraints on PBHs with 10 16 g to 10 25 g. ...
Preprint
Following a new microlensing constraint on primordial black holes (PBHs) with 1020\sim10^{20}--1028g10^{28}\,\mathrm{g}~[1], we revisit the idea of PBH as all Dark Matter (DM). We have shown that the updated observational constraints suggest the viable mass function for PBHs as all DM to have a peak at 1020g\simeq 10^{20}\,\mathrm{g} with a small width σ0.1\sigma \lesssim 0.1, by imposing observational constraints on an extended mass function in a proper way. We have also provided an inflation model that successfully generates PBHs as all DM fulfilling this requirement.
... Collisions of axion drops with white dwarfs and neutron stars [58] have been proposed as a source for GRBs, as well as to explain other anomalies. However the energy released in the collision of a drop with a neutron star is controversial [30] (as is also the case for the interactions of primordial black holes with neutron stars [50,59,60]). ...
Preprint
We consider how QCD axions produced by the misalignment mechanism could form galactic dark matter halos. We recall that stationary, gravitationally stable axion field configurations have the size of an asteroid with masses of order 101310^{-13} solar masses (because gradient pressure is insufficient to support a larger object). We call such field configurations "drops". We explore whether rotating drops could be larger, and find that their mass could increase by a factor ~ 10. Remarkably this mass is comparable to the mass of miniclusters generated from misalignment axions in the scenario where the axion is born after inflation. We speculate that misalignment axions today are in the form of drops, contributing to dark matter like a distribution of asteroids (and not as a coherent oscillating background field). We consider some observational signatures of the drops, which seem consistent with a galactic halo made of axion dark matter.
... where M is the neutron star mass and v esc = (2GM/R) 1/2 . Recalling our discussion on the adiabatic resonance in §3 (the efficient conversion can occur for m 2 γ (r res ) ≈ m 2 a with the resonance width ∆m 2 γ ≈ 4gBω), we can estimate that the axion mass going through the efficient axion-photon conversion region is of order [45][46][47][48] ...
Preprint
We study the conditions for the adiabatic resonant conversion of the cold dark matter (CDM) axions into photons in existence of the astrophysically sourced strong magnetic fields such as those in the neutron star magnetosphere. We demonstrate the possibility that the forthcoming radio telescopes such as the SKA (Square Kilometre Array) can probe those photon signals from the CDM axions.
... Thus for the moment we cut the constraint below 10 −10 M by hand. There are also constraints from dynamical processes such as destruction of white dwarfs by PBHs [96,97] and absorption of neutron stars by PBHs [98]. [100,101]. ...
Preprint
We study possibilities to explain the whole dark matter abundance by primordial black holes (PBHs) or to explain the merger rate of binary black holes estimated from the gravitational wave detections by LIGO/Virgo. We assume that the PBHs are originated in a radiation- or matter-dominated era from large primordial curvature perturbation generated by inflation. We take a simple model-independent approach considering inflation with large running spectral indices which are parametrized by ns,αsn_\text{s}, \alpha_\text{s}, and βs\beta_\text{s} consistent with the observational bounds. The merger rate is fitted by PBHs with masses of O(10)\mathcal{O}(10) MM_{\odot} produced in the radiation-dominated era. Then the running of running should be βs0.025\beta_\text{s} \sim 0.025, which can be tested by future observation. On the other hand, the whole abundance of dark matter is consistent with PBHs with masses of asteroids (O(1017) M\mathcal{O}(10^{-17})~M_{\odot}) produced in an early matter-dominated era if a set of running parameters are properly realized.
... This expression does not assume spherical symmetry in the initial density profile. Using data from the plot of ρ PBH /ρ DM against M PBH from [40] (which is in turn collated from constraints due to evaporation [1], femto-lensing of gamma-ray bursts [41], neutron-star capture [42], white dwarf explosions [43], microlensing [2,44,45], Planck results [46], survival of stars in Segue I [47] and Eridanus II [48], and distribution of wide binaries [49]), it is possible to scale the observed constraints on PBH abundance such that they include a period of evolution in the matter dominated phase. Taking constraints on ρ PBH /ρ DM from [40], we can relate them to constraints on β(M ) via ...
Preprint
Observational constraints on the abundance of primordial black holes (PBHs) constrain the allowed amplitude of the primordial power spectrum on both the smallest and the largest ranges of scales, covering over 20 decades from 11020/Mpc1-10^{20}/ \rm{Mpc}. Despite tight constraints on the allowed fraction of PBHs at their time of formation near horizon entry in the early universe, the corresponding constraints on the primordial power spectrum are quite weak, typically PR102{\cal P}_\mathcal{R}\lesssim 10^{-2} assuming Gaussian perturbations. Motivated by recent claims that the evaporation of just one PBH would destabilise the Higgs vacuum and collapse the universe, we calculate the constraints which follow from assuming there are zero PBHs within the observable universe. This extends the constraints right down to the horizon scale at the end of inflation, but does not significantly tighten the existing power spectrum constraints, even though the constraint on PBH abundance can decrease by up to 46 orders of magnitude. This shows that no future improvement in observational constraints can ever lead to a significant tightening in constraints on inflation (via the power spectrum amplitude). The power spectrum constraints are weak because an order unity perturbation is required in order to overcome pressure forces. We therefore consider an early matter dominated era, during which exponentially more PBHs form for the same initial conditions. We show this leads to far tighter constraints, which approach PR109{\cal P}_\mathcal{R}\lesssim10^{-9}, albeit over a smaller range of scales and are very sensitive to when the early matter dominated era ends. Finally, we show that an extended early matter era is incompatible with the argument that an evaporating PBH would destroy the universe, unless the power spectrum amplitude decreases by up to ten orders of magnitude.
... To detect and study these primordial black holes, a plethora of methods and experiments have been proposed, aiming to illuminate the properties, abundance, and implications of PBHs and provide valuable insights into the nature of dark matter. These include microlensing surveys [10][11][12][13], investigations of cosmic microwave background anisotropies [14,15], evaporations on big bang nucleosynthesis and the extragalactic photon background [16,17], analysis of gamma-ray radiation [18][19][20][21][22][23], detection of PBH-generated gravitational waves [24][25][26][27][28][29][30], and examination of astrophysics surveys [31][32][33]. ...
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Primordial black holes (PBHs), originating from the gravitational collapse of large overdensities in the early Universe, emerge as a compelling dark matter (DM) candidate across a broad mass range. Of particular interest are ultra-light PBHs with masses around 101410^{14} to 101710^{17} g, which are typically probed by searching their evaporation products. Using the soft X-ray signal measured by the XMM telescopes, we derive constraints on the fraction of PBHs dark matter with masses in the range 101510^{15}-101610^{16} g. We find that observations exclude fraction f>106f>10^{-6} at 95\% C.L. for mass MPBH=1015M_{\rm PBH}=10^{15} g.
... Compact dark matter objects could be gravitationally captured by neutron stars [54] or white dwarfs [55], triggering instability and leading to constraints on compact objects with mass M ≲ 10 −12 M ⊙ . Such constraints are unlikely to be relevant for axion relic pockets, given that the large magnetic fields produced by neutron stars and white dwarfs would likely lead to axion-photon conversion rather than capture (see below). ...
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A bstract We propose a new theory of dark matter based on axion physics and cosmological phase transitions. We show that theories in which a gauge coupling increases through a first-order phase transition naturally result in ‘axion relic pockets’: regions of relic false vacua stabilised by the pressure from a kinematically trapped, hot axion gas. Axion relic pockets provide a viable and highly economical theory of dark matter: the macroscopic properties of the pockets depend only on a single parameter (the phase transition temperature). We describe the formation, evolution and present-day properties of axion relic pockets, and outline how their phenomenology is distinct from existing dark matter paradigms. We briefly discuss how laboratory experiments and astronomical observations can be used to test the theory, and identify gamma-ray observations of magnetised, dark-matter-dense environments as particularly promising.
... They are eligible to be candidates of nonbaryonic dark matter. This mass falls within the range 10 17 −10 22 g, which is unconstrained and hence is open as a window that provides all of the dark matter density in the Universe (Capela et al. 2013a(Capela et al. , 2013b. PBHs within the above range are produced through isocurvature density perturbations in specific inflationary models and thereby contribute to scalar-induced gravitational wave (SIGW) signals with frequencies ranging from nHz to kHz (Ahmed et al. 2022). ...
Article
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f ( R ) gravity is one of the serious alternatives of general relativity with a large range of astronomical consequences. In this work, we study Big Bang nucleosynthesis (BBN) in f ( R ) gravity theory. We consider a modification to gravity due to the existence of primordial black holes (PBHs) in the radiation era that introduce additional degrees of freedom known as scalarons. We calculate the light element abundances by using the BBN code PArthENoPE . It is found that for a range of scalaron mass (2.2 − 3.5) × 10 ⁴ eV, the abundance of lithium is lowered by 3−4 times the value predicted by general relativistic BBN, which is a level desired to address the cosmological lithium problem. For the above scalaron mass range, the helium abundance is within the observed bound. However, the deuterium abundance is found to be increased by 3−6 times the observed primordial abundance. It calls for a high efficiency of stellar formation and evolution processes for the destruction of primordial deuterium, which is suggested as possible in scalaron gravity. A novel relation between scalaron mass and black hole mass has been used to show that the above scalaron mass range corresponds to PBHs of subplanetary mass (∼10 ¹⁹ g) serving as one of the potential candidates of nonbaryonic dark matter. We infer Big Bang equivalence of power-law f ( R ) gravity with PBHs that are detectable with upcoming gravitational wave detectors.
... Afshordi et al. [103] showed that the Poisson fluctuations in the PBH distribution would lead to the formation of PBH clusters shortly after matter-radiation equality and the enhanced clustering on subgalactic scales would have important implications for observations of Lyman-alpha clouds. It was also suggested that asteroid-mass PBHs (10 17 g ≲ M ≲ 10 22 g) could be probed via the consequences of their interactions with stars [104][105][106]. ...
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We overview the history of primordial black hole (PBH) research from the first papers around 50 years ago to the present epoch. The history may be divided into four periods, the dividing lines being marked by three key developments: inflation on the theoretical front and the detection of microlensing events by the MACHO project and gravitational waves by the LIGO/Virgo/KAGRA project on the observation front. However, they are also characterised by somewhat different focuses of research. The period 1967-1980 covered the groundbreaking work on PBH formation and evaporation. The period 1980-1996 mainly focussed on their formation, while the period 1996-2016 consolidated the work on formation but also collated the constraints on the PBH abundance. In the period 2016-2024 there was a shift of emphasis to the search for evidence for PBHs and - while opinions about the strength of the purported evidence vary - this has motivated more careful studies of some aspects of the subject. Certainly the soaring number of papers on PBHs in this last period indicates a growing interest in the topic.
... Furthermore, the fractional abundances can exceed constraints, such as those given in Refs. [113,114]. As mentioned, the proper adjustment of parameters for each model is required, but this is beyond the scope of this paper. ...
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In this study, we present an analysis of the fine-tuning required in various inflationary models in order to explain the production of Primordial Black Holes (PBHs). We specifically examine the degree of fine-tuning necessary in two prominent single-field inflationary models: those with an inflection point and those with step-like features in the potential. Our findings indicate that models with step-like features generally require less fine-tuning compared to those with an inflection point, making them more viable for consistent PBH production. An interesting outcome of these models is that, in addition to improved fine-tuning, they may also predict low-frequency signals that can be detected by pulsar timing array (PTA) collaborations. Additionally, we extend our analysis to multifield inflationary models to assess whether the integration of additional fields can further alleviate the fine-tuning demands. The study also explores the role of a spectator field and its impact on the fine-tuning process. Our results indicate that although mechanisms involving a spectator field can circumvent the issue of fine-tuning parameters for PBH production, both multifield models and models with step-like features present promising alternatives. While fine-tuning involves multiple considerations, our primary objective is to evaluate various inflationary models to identify the one that most naturally explains the formation of PBHs. Hence, this study introduces a novel approach by categorizing existing PBH mechanisms, paving the way for subsequent research to prioritize models that minimize the need for extensive fine-tuning.
... Solar-mass BHs are not typically expected to form through the usual stellar collapse. However, such BHs can emerge as PBHs or naturally form through the implosion of NSs, which can be triggered by the capture of sub-solar-mass objects that make up dark matter (e.g., Capela et al. 2013;Fuller et al. 2017;Bramante et al. 2018;Takhistov et al. 2021). ...
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In this work, we investigate the merger rate of primordial black hole–neutron star (PBH-NS) binaries in two widely studied modified gravity (MG) models: Hu–Sawicki f(R) gravity and the normal branch of Dvali–Gabadadze–Porrati gravity. In our analysis, we take into account the effects of MG on the halo properties, including halo mass function, halo concentration parameter, halo density profile, and velocity dispersion of dark matter particles. We find that these MG models, due to their stronger gravitational field induced by an effective fifth force, predict enhanced merger rates compared to general relativity. This enhancement is found to be redshift-dependent and sensitive to model parameters and PBH mass and fraction. Assuming a PBH mass range of 5–50 M_sun, we compare the predicted merger rate of PBH-NS binaries with those inferred from LIGO–Virgo–KAGRA observations of gravitational waves (GWs). We find that the merger rates obtained from MG models will be consistent with the GW observations if the abundance of PBHs is relatively large, with the exact amount depending on the MG model and its parameter values, as well as PBH mass. We also establish upper limits on the abundance of PBHs in these MG frameworks while comparing them with the existing non-GW constraints, which can potentially impose even more stringent constraints.
... The most natural hypothesis that explains such discrepancies consists in the presence of some kind of matter which is not detectable through electromagnetic interaction: the so-called dark matter (DM) [15]. About the exact nature of the DM, many speculations have been proposed: it being constituted by hypothetical particles with a big mass, interacting only via the weak force (the WIMPs, Weakly Interactive Massive Particles) [16,17,18,19,20]; or by lighter particles whose field auto-interacts (the ALPs, Axion-Like Particles) [21], so that the dark matter halos would be the solitonic solutions of its field equation; or even by macroscopic opaque objects (the MACHOs, MAssive Compact Halo Objects) [22,23,24,25]. However, alternative explanations of the Missing Mass Problem, avoiding the presence of actual matter, have been proposed. ...
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In recent years, there has been an increase in the number of papers regarding general-relativistic explanations for the dark matter phenomena in disc galaxies. The main focus of this scientific discussion is whether a previously unexamined relativistic dragging vortex could support flat rotation curves, with various research groups taking different stances on its feasibility. In this paper, we discuss the different points of view by placing the various arguments within a general theoretical context. We explicitly state the conceptual assumptions, and indicate what we believe to be the correct interpretation for the physical quantities of interest. We show how the dragging conjecture fails under certain hypotheses, and discuss the flaws of the most common dragging models: the linearised gravitomagnetic description and the one of Balasin & Grumiller. On the other hand, we illustrate how to avoid failure scenarios for the conjecture, emphasizing the features for a physically reasonable disc galaxy dragging model. In particular, we stress that the non-linearities of the Einstein Equations must play an essential role in generating what we define as "pseudo-solitonic" solutions-the only non-trivial physically viable solutions for the class of models considered. Furthermore, the dragging vortex is proven to show important contributions to the gravitational lensing in these models, thus providing an ulterior measure of its relevance. Moreover, by qualitatively exploring these pseudo-solitonic solutions, we find that a dragging speed of just a few kilometers per second would be enough to explain a non-negligible fraction of the galactic dark matter. Finally, we propose and analyse the feasibility of three independent measurements which could be carried out to detect the presence of dragging vortices in disc galaxies.
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In the recent years, primordial black holes (PBHs) have emerged as one of the most interesting and hotly debated topics in cosmology. Among other possibilities, PBHs could explain both some of the signals from binary black hole mergers observed in gravitational-wave detectors and an important component of the dark matter in the Universe. Significant progress has been achieved both on the theory side and from the point of view of observations, including new models and more accurate calculations of PBH formation, evolution, clustering, merger rates, as well as new astrophysical and cosmological probes. In this work, we review, analyze and combine the latest developments in order to perform end-to-end calculations of the various gravitational-wave signatures of PBHs. Different ways to distinguish PBHs from stellar black holes are emphasized. Finally, we discuss their detectability with LISA, the first planned gravitational-wave observatory in space.
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It is a common belief that a theory of quantum gravity should ultimately cure curvature singularities which are inevitable within general relativity, and plague for instance the Schwarzschild and Kerr metrics, usually considered as prototypes for primordial black holes (PBHs) as dark matter (DM) candidates. We continue our study, initiated in a companion paper, of nonsingular objects as PBHs, considering three regular non-𝑡⁢𝑟 (non-time-radial)-symmetric metrics, all of which are one-parameter extensions of the Schwarzschild space-time: the Simpson-Visser, Peltola-Kunstatter, and D’Ambrosio-Rovelli space-times, with the latter two motivated by loop quantum gravity. We study evaporation constraints on PBHs described by these regular metrics, deriving upper limits on 𝑓pbh, the fraction of DM in the form of PBHs. Compared to their Schwarzschild counterparts, these limits are weaker, and result in a larger asteroid mass window where all the DM can be in the form of PBHs, with the lower edge moving potentially more than an order of magnitude. Our work demonstrates as a proof-of-principle that quantum gravity-inspired space-times can simultaneously play an important role in the resolution of singularities and in the DM problem.
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Dense strange quark matter (SQM) composed of up, down, and strange quarks may be the absolute ground state of strong-interaction matter. Based on this SQM hypothesis, pulsars may actually be strange stars. Strange stars are different from conventional neutron stars in features such as mass-radius relationship and cooling rate, but current astronomical observations cannot discriminate between them unambiguously yet. Strange stars can power fast radio bursts and gravitational-wave bursts. The ultimate stability of SQM enables self-bound planetary-mass SQM clumps, i.e. strange planets, to exist stably. A strange planet, being very dense, can revolve around a central object in a very close orbit with a period shorter than 6 100 s. By contrast, a plant made up of normal matter shall be tidally disrupted at such a short distance. Therefore, these close-in planetary systems would strongly evidence the existence of strange planets once they were discovered. Moreover, strange dwarfs can stably exist under the SQM hypothesis. Future multiwavelength and multimessenger astronomical observations may help clarify the nature of dense matter.
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Lacking terrestrial experimental data, our best constraints on the behavior of matter at high densities up to and above nuclear density arise from observations of neutron stars. Current constraints include those based on measurements of stellar masses, radii, and tidal deformabilities. Here we explore how orbits of primordial black holes—should they exist—inside neutron stars could provide complementary constraints on the nuclear equation of state (EOS). Specifically, we consider a sample of candidate EOSs, construct neutron star models for these EOSs, and compute orbits of primordial black holes inside these stars. We discuss how the pericenter advance of eccentric orbits, i.e. orbital precession, results in beat phenomena in the emitted gravitational wave signal. Observing this beat frequency could constrain the nuclear EOS and break possible degeneracies arising from other contraints, as well as provide information about the host star.
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Primordial black holes (PBHs) remain a viable dark matter candidate in the asteroid-mass range. We point out that, in this scenario, the PBH abundance would be large enough for at least one object to cross through the inner Solar System per decade. Since Solar System ephemerides are modeled and measured to extremely high precision, such close encounters could produce detectable perturbations to orbital trajectories with characteristic features. We evaluate this possibility with a suite of simple Solar System simulations, and we argue that the abundance of asteroid-mass PBHs can plausibly be probed by existing and near-future data.
Preprint
A very pressing question in contemporary physics is the identity of Dark Matter (DM), and one that has not been answered affirmatively to any degree so far. Primordial Black Holes (PBHs) are one of the most well-motivated DM candidates. Light enough PBHs have been constrained by either the non-detection of their Hawking radiation itself, or by the non-observation of any measurable effects of this radiation on astrophysical and cosmological observables. We constrain the PBH density by their Hawking radiation effect on the intergalactic medium (IGM) temperature evolution. We use the latest deductions of IGM temperature from Lyman-α\alpha forest observations. We put constraints on the fraction of PBH DM with masses 5×10155 \times 10^{15} g - 101710^{17} g separately for spinning and non-spinning BHs. We derive constraints by dealing with the heating effects of the astrophysical reionization of the IGM in two ways. In one way, we completely neglect this heating due to astrophysical sources, thus giving us weaker constraints, but completely robust to the reionization history of the universe. In the second way, we utilise some modelling of the ionization and temperature history, and use it to derive more stringent constraints. We find that for non-spinning PBHs of mass 101610^{16} g, the current measurements can constrain the PBH-density to be \lesssim 0.1% of the total DM. We find that these constraints from the latest Lyman-α\alpha forest temperature measurements are competitive, and hence provide a new observable to probe the nature of PBH DM. The systematics affecting Lyman-α\alpha forest measurements are different from other constraining observations, and thus this is a complementary probe.
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A sub-solar mass primordial black hole (PBH) passing through a neutron star, can lose enough energy through interactions with the dense stellar medium to become gravitationally bound to the star. Once captured, the PBH would sink to the core of the neutron star, and completely consume it from the inside. In this paper, we improve previous energy-loss calculations by considering a realistic solution for the neutron star interior, and refine the treatment of the interaction dynamics and collapse likelihood. We then consider the effect of a sub-solar PBH population on neutron stars near the Galactic center. We find that it is not possible to explain the lack of observed pulsars near the galactic center through dynamical capture of PBHs, as the velocity dispersion is too high. We then show that future observations of old neutron stars close to Sgr A* could set stringent constraints on the PBHs abundance. These cannot however be extended in the currently unconstrained asteroid-mass range, since PBHs of smaller mass would lose less energy in their interaction with the neutron star and end up in orbits that are too loosely bound and likely to be disrupted by other stars in the Galactic center.
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We present self-consistent numerical simulations in general relativity of putative primordial black holes inside neutron stars. Complementing a companion paper in which we assumed the black-hole mass m to be much smaller than the mass M* of the neutron star, thereby justifying a point-mass treatment, we here consider black holes with masses large enough so that their effect on the neutron star cannot be neglected. We develop and employ several new numerical techniques, including initial data describing boosted black holes in neutron-star spacetimes, a relativistic determination of the escape speed, and a gauge condition that keeps the black hole at a fixed coordinate location. We then perform numerical simulations that highlight different aspects of the capture of primordial black holes by neutron stars. In particular, we simulate the initial passage of the black hole through the star, demonstrating that the neutron star remains dynamically stable provided the black-hole mass is sufficiently small, m≲0.05M*. We model the late evolution of a black hole oscillating about the center of an initially stable neutron star while accreting stellar mass and ultimately triggering gravitational collapse.
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Primordial black holes (PBHs), if trapped in neutron stars, emit a characteristic continuous, quasiperiodic gravitational wave (GW) signal as they orbit inside the host star. We identify a specific and qualitatively new feature of these signals, namely quasiperiodic beats caused by the precession of noncircular PBH orbits. We demonstrate numerically and analytically that the beat frequency depends rather sensitively on the neutron star structure, so that hypothetical future observations with next-generation GW detectors could provide valuable constraints on the nuclear equation of state.
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Primordial black holes (PBHs), if they exist, may collide with and be captured by neutron stars. We adopt a relativistic point-mass approximation to study this capture, the subsequent confinement of the PBH of mass m inside the neutron star of mass M*≫m, and the PBH’s growth by accretion of stellar material. Building on earlier treatments we systematically study the capture, confinement, and accretion process, characterize the emitted quasiperiodic continuous gravitational-wave signal, track the evolution of the PBH’s orbital parameters, and compare the effects of different choices for the prescription of the dissipative forces. Our point-mass treatment here is applicable in the limit of small PBH masses, for which its effects on the neutron star can be ignored.
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Primordial black holes (PBHs) could explain some fraction of dark matter and shed light on many areas of early-Universe physics. Despite over half a century of research interest, a PBH population has so far eluded detection. The most competitive constraints on the fraction of dark matter comprised of PBHs ( f DM ) in the (10 ⁻⁹ –10) M ⊙ mass ranges come from photometric microlensing and bound f DM ≲ 10 ⁻² –10 ⁻¹ . With the advent of the Roman Space Telescope with its submilliarcsecond astrometric capabilities and its planned Galactic Bulge Time Domain Survey (GBTDS), detecting astrometric microlensing signatures will become routine. Compared with photometric microlensing, astrometric microlensing signals are sensitive to different lens masses–distance configurations and contain different information, making it a complimentary lensing probe. At submilliarcsecond astrometric precision, astrometric microlensing signals are typically detectable at larger lens–source separations than photometric signals, suggesting a microlensing detection channel of pure astrometric events. We use a Galactic simulation to predict the number of detectable microlensing events during the GBTDS via this pure astrometric microlensing channel. Assuming an absolute astrometric precision floor for bright stars of 0.1 mas for the GBTDS, we find that the number of detectable events peaks at ≈10 ³ f DM for a population of 1 M ⊙ PBHs and tapers to ≈10 f DM and ≈100 f DM at 10 ⁻⁴ M ⊙ and 10 ³ M ⊙ , respectively. Accounting for the distinguishability of PBHs from stellar lenses, we conclude the GBTDS will be sensitive to a PBH population at f DM down to ≈10 ⁻¹ –10 ⁻³ for (10 ⁻¹ –10 ² ) M ⊙ likely yielding novel PBH constraints.
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The capture of dark matter, and its subsequent annihilation, can heat old, isolated neutron stars. In order for kinetic heating to be achieved, the captured dark matter must undergo sufficient scattering to deposit its kinetic energy in the star. We find that this energy deposit typically occurs quickly, for most of the relevant parameter space. In order for appreciable annihilation heating to also be achieved, the dark matter must reach a state of capture-annihilation equilibrium in the star. We show that this can be fulfilled for all types of dark matter-baryon interactions. This includes cases where the scattering or annihilation cross sections are momentum or velocity suppressed in the non-relativistic limit. Importantly, we find that capture-annihilation equilibrium, and hence maximal annihilation heating, can be achieved without complete thermalization of the captured dark matter. For scattering cross sections that saturate the capture rate, we find that capture-annihilation equilibrium is typically reached on a timescale of less than 1 year for vector interactions and 10⁴ years for scalar interactions.
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The all-sky survey in high-energy gamma rays (E > 30 MeV) carried out by EGRET aboard the Compton Gamma Ray Observatory provides a unique opportunity to examine in detail the diffuse gamma-ray emission. The observed diffuse emission has a Galactic component arising from cosmic-ray interactions with the local interstellar gas and radiation, as well as an almost uniformly distributed component that is generally believed to originate outside the Galaxy. Through a careful study and removal of the Galactic diffuse emission, the flux, spectrum, and uniformity of the extragalactic emission are deduced. The analysis indicates that the extragalactic emission is well described by a power-law photon spectrum with an index of -(2.10 ± 0.03) in the 30 MeV to 100 GeV energy range. No large-scale spatial anisotropy or changes in the energy spectrum are observed in the deduced extragalactic emission. The most likely explanation for the origin of this extragalactic high-energy gamma-ray emission is that it arises primarily from unresolved gamma-ray-emitting blazars.
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We impose new severe constraints on the self-interactions of fermionic asymmetric dark matter based on observations of nearby old neutron stars. WIMP self-interactions mediated by Yukawa- type interactions can lower significantly the number of WIMPs necessary for gravitational collapse of the WIMP population accumulated in a neutron star. Even nearby neutron stars located at regions of low dark matter density can accrete sufficient number of WIMPs that can potentially collapse, form a mini black hole, and destroy the host star. Based on this, we derive constraints on the WIMP self-interactions which in some cases are by several orders of magnitude stricter than the ones from the bullet cluster (which are currently considered the most stringent).
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Recently, constraints on bosonic asymmetric dark matter have been imposed based on the existence of old neutron stars excluding the dark matter masses in the range from 2\sim 2 keV up to several GeV. The constraints are based on the star destruction scenario where the dark matter particles captured by the star collapse forming a black hole that eventually consumes the host star. In addition, there were claims in the literature that similar constraints can be obtained for dark matter masses heavier than a few TeV. Here we argue that it is not possible to extend to these constraints. We show that in the case of heavy dark matter, instead of forming a single large black hole that consumes the star, the collapsing dark matter particles form a series of small black holes that evaporate fast without leading to the destruction of the star. Thus, no constraints arise for bosonic asymmetric dark matter particles with masses of a few TeV or higher.
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The horizontal branch (HB) morphology of globular clusters (GCs) is most strongly influenced by metallicity. The second parameter phenomenon, first described in the 1960s, acknowledges that metallicity alone is not enough to describe the HB morphology of all GCs. In particular, astronomers noticed that the outer Galactic halo contains GCs with redder HBs at a given metallicity than are found inside the solar circle. Thus, at least a second parameter was required to characterize HB morphology. While the term "second parameter" has since come to be used in a broader context, its identity with respect to the original problem has not been conclusively determined. Here we analyze the median color difference between the HB and the red giant branch, hereafter denoted as Δ(V – I), measured from Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) photometry of 60 GCs within ~20 kpc of the Galactic center. Analysis of this homogeneous data set reveals that, after the influence of metallicity has been removed from the data, the correlation between Δ(V – I) and age is stronger than that of any other parameter considered. Expanding the sample to include HST ACS and Wide Field Planetary Camera 2 photometry of the six most distant Galactic GCs lends additional support to the correlation between Δ(V – I) and age. This result is robust with respect to the adopted metallicity scale and the method of age determination, but must bear the caveat that high-quality, detailed abundance information is not available for a significant fraction of the sample. Furthermore, when a subset of GCs with similar metallicities and ages is considered, a correlation between Δ(V – I) and central luminosity density is exposed. With respect to the existence of GCs with anomalously red HBs at a given metallicity, we conclude that age is the second parameter and central density is most likely the third. Important problems related to HB morphology in GCs, notably multi-modal distributions and faint blue tails, remain to be explained.
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The EROS and MACHO collaborations have each published upper limits on the amount of planetary-mass dark matter in the Galactic halo obtained from gravitational microlensing searches. In this Letter, the two limits are combined to give a much stronger constraint on the abundance of low-mass MACHOs. Specifically, objects with masses 10−7 Mm10−3 M make up less than 25% of the halo dark matter for most models considered, and less than 10% of a standard spherical halo is made of MACHOs in the 3.5×10−7 M<m<4.5×10−5 M mass range.
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The abundance of primordial black holes is currently significantly constrained in a wide range of masses. The weakest limits are established for the small mass objects, where the small intensity of the associated physical phenomenon provides a challenge for current experiments. We used gamma- ray bursts with known redshifts detected by the Fermi Gamma-ray Burst Monitor (GBM) to search for the femtolensing effects caused by compact objects. The lack of femtolensing detection in the GBM data provides new evidence that primordial black holes in the mass range 5 \times 10^{17} - 10^{20} g do not constitute a major fraction of dark matter.
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We argue that current neutron star observations exclude asymmetric bosonic noninteracting dark matter in the range from 2 keV to 16 GeV, including the 5-15 GeV range favored by DAMA and CoGeNT. If bosonic weakly interacting massive particles (WIMPs) are composite of fermions, the same limits apply provided the compositeness scale is higher than ∼10¹²  GeV (for WIMP mass ∼1  GeV). In the case of repulsive self-interactions, we exclude the large range of WIMP masses and interaction cross sections which complements the constraints imposed by observations of the Bullet Cluster.
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We put constraints on asymmetric dark matter candidates with spin-dependent interactions based on the simple existence of white dwarfs and neutron stars in globular clusters. For a wide range of the parameters (WIMP mass and WIMP-nucleon cross section), WIMPs can be trapped in progenitors in large numbers and once the original star collapses to a white dwarf or a neutron star, these WIMPs might self-gravitate and eventually collapse forming a mini-black hole that eventually destroys the star. We impose constraints competitive to direct dark matter search experiments, for WIMPs with masses down to the TeV scale.
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We argue that observations of old neutron stars can impose constraints on dark matter candidates even with very small elastic or inelastic cross section, and self-annihilation cross section. We find that old neutron stars close to the galactic center or in globular clusters can maintain a surface temperature that could in principle be detected. Due to their compactness, neutron stars can acrete WIMPs efficiently even if the WIMP-to-nucleon cross section obeys the current limits from direct dark matter searches, and therefore they could constrain a wide range of dark matter candidates. Comment: 20 pages, 5 figures
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Observed metallicities of globular clusters reflect physical conditions in the interstellar medium of their high-redshift host galaxies. Globular cluster systems in most large galaxies display bimodal color and metallicity distributions, which are often interpreted as indicating two distinct modes of cluster formation. The metal-rich and metal-poor clusters have systematically different locations and kinematics in their host galaxies. However, the red and blue clusters have similar internal properties, such as the masses, sizes, and ages. It is therefore interesting to explore whether both metal-rich and metal-poor clusters could form by a common mechanism and still be consistent with the bimodal distribution. We present such a model, which prescribes the formation of globular clusters semi-analytically using galaxy assembly history from cosmological simulations coupled with observed scaling relations for the amount and metallicity of cold gas available for star formation. We assume that massive star clusters form only during mergers of massive gas-rich galaxies and tune the model parameters to reproduce the observed distribution in the Galaxy. A wide, but not entire, range of model realizations produces metallicity distributions consistent with the data. We find that early mergers of smaller hosts create exclusively blue clusters, whereas subsequent mergers of more massive galaxies create both red and blue clusters. Thus bimodality arises naturally as the result of a small number of late massive merger events. This conclusion is not significantly affected by the large uncertainties in our knowledge of the stellar mass and cold gas mass in high-redshift galaxies. The fraction of galactic stellar mass locked in globular clusters declines from over 10% at z>3 to 0.1% at present. Comment: matches version accepted by ApJ
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Aims. The EROS-2 project was designed to test the hypothesis that massive compact halo objects (the so-called “machos”) could be a major component of the dark matter halo of the Milky Way galaxy. To this end, EROS-2 monitored over 6.7 years 33×10633\times10^6 stars in the Magellanic clouds for microlensing events caused by such objects. Methods. In this work, we use only a subsample of 7×1067\times10^6 bright stars spread over 84deg284\,\rm deg^2 of the LMC and 9deg29\,\rm deg^2 of the SMC. The strategy of using only bright stars helps to discriminate against background events due to variable stars and allows a simple determination of the effects of source confusion (blending). The use of a large solid angle makes the survey relatively insensitive to effects that could make the optical depth strongly direction dependent. Results. Using this sample of bright stars, only one candidate event was found, whereas ~39 events would have been expected if the Halo were entirely populated by objects of mass M0.4 MM\sim0.4~M_{\odot}. Combined with the results of EROS-1, this implies that the optical depth toward the Large Magellanic Cloud (LMC) due to such lenses is τ<0.36×107\tau<0.36\times10^{-7} (95% CL), corresponding to a fraction of the halo mass of less than 8%. This optical depth is considerably less than that measured by the MACHO collaboration in the central region of the LMC. More generally, machos in the mass range 0.6×107M<M<15 M0.6\times10^{-7}M_\odot<M<15~M_{\odot} are ruled out as the primary occupants of the Milky Way Halo.
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It was suggested by several authors that hypothetical primordial black holes (PBHs) may contribute to the dark matter (DM) in our Galaxy. There are strong constraints based on the Hawking evaporation that practically exclude PBHs with masses m pbh ~ 1015to1016 g and smaller as significant contributors to the Galactic DM. Similarly, PBHs with masses greater than about 1026 g are practically excluded by the gravitational lensing observation. The mass range between 1016 g <m pbh < 1026 g is unconstrained. In this paper, we examine possible observational signatures in the unexplored mass range, investigating hypothetical collisions of PBHs with main-sequence stars, red giants, white dwarfs, and neutron stars in our Galaxy. This has previously been discussed as possibly leading to an observable photon eruption due to shock production during the encounter. We find that such collisions are either too rare to be observed (if the PBH masses are typically larger than about 1020 g), or produce too little power to be detected (if the masses are smaller than about 1020 g).
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In this second paper in our series, we continue to test primordial scenarios of globular cluster formation which predict that globular clusters formed in the early universe in the potential of dark matter minihalos. In this paper we use high-resolution N-body simulations to model tidal stripping experienced by primordial dark-matter dominated globular clusters in the static gravitational potential of the host dwarf galaxy. We test both cuspy Navarro-Frenk-White (NFW) and flat-core Burkert models of dark matter halos. Our primordial globular cluster with an NFW dark matter halo survives severe tidal stripping, and after 10 orbits is still dominated by dark matter in its outskirts. Our cluster with Burkert dark matter halo loses almost all its dark matter to tidal stripping, and starts losing stars at the end of our simulations. The results of this paper reinforce our conclusion in Paper I that current observations of globular clusters are consistent with the primordial picture of globular cluster formation. Comment: 12 pages, 9 figures. Astrophysical Journal, in press
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In a series of two papers, we test the primordial scenario of globular cluster formation using results of high-resolutions N-body simulations. In this first paper we study the initial relaxation of a stellar core inside a live dark matter minihalo in the early universe. Our dark-matter dominated globular clusters show features which are usually attributed to the action of the tidal field of the host galaxy. Among them are the presence of an apparent cutoff ("tidal radius") or of a "break" in the outer parts of the radial surface brightness profile, and a flat line-of-sight velocity dispersion profile in the outskirts of the cluster. The apparent mass-to-light ratios of our hybrid (stars + dark matter) globular clusters are very close to those of purely stellar clusters. We suggest that additional observational evidence such as the presence of obvious tidal tails is required to rule out the presence of significant amounts of dark matter in present day globular clusters. Comment: 14 pages, 9 figures. Astrophysical Journal, in press
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We study the effect of WIMP annihilation on the temperature of a neutron star. We shall argue that the released energy due to WIMP annihilation inside the neutron stars, might affect the temperature of stars older than 10 million years, flattening out the temperature at 104\sim 10^4 K for a typical neutron star.
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Non-baryonic, or "dark," matter is believed to be a major component of the total mass budget of the universe. We review the candidates for particle dark matter and discuss the prospects for direct detection (via interaction of dark matter particles with laboratory detectors) and indirect detection (via observations of the products of dark matter self-annihilations), focusing in particular on the Galactic center, which is among the most promising targets for indirect detection studies. The gravitational potential at the Galactic center is dominated by stars and by the supermassive black hole, and the dark matter distribution is expected to evolve on sub-parsec scales due to interaction with these components. We discuss the dominant interaction mechanisms and show how they can be used to rule out certain extreme models for the dark matter distribution, thus increasing the information that can be gleaned from indirect detection searches.
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QUANTUM gravitational effects are usually ignored in calculations of the formation and evolution of black holes. The justification for this is that the radius of curvature of space-time outside the event horizon is very large compared to the Planck length (Għ/c3)1/2 ~ 10-33 cm, the length scale on which quantum fluctuations of the metric are expected to be of order unity. This means that the energy density of particles created by the gravitational field is small compared to the space-time curvature. Even though quantum effects may be small locally, they may still, however, add up to produce a significant effect over the lifetime of the Universe ~ 1017 s which is very long compared to the Planck time ~ 10-43 s. The purpose of this letter is to show that this indeed may be the case: it seems that any black hole will create and emit particles such as neutrinos or photons at just the rate that one would expect if the black hole was a body with a temperature of (κ/2π) (ħ/2k) ~ 10-6 (Msolar/M)K where κ is the surface gravity of the black hole1. As a black hole emits this thermal radiation one would expect it to lose mass. This in turn would increase the surface gravity and so increase the rate of emission. The black hole would therefore have a finite life of the order of 1071 (Msolar/M)-3 s. For a black hole of solar mass this is much longer than the age of the Universe. There might, however, be much smaller black holes which were formed by fluctuations in the early Universe2. Any such black hole of mass less than 1015 g would have evaporated by now. Near the end of its life the rate of emission would be very high and about 1030 erg would be released in the last 0.1 s. This is a fairly small explosion by astronomical standards but it is equivalent to about 1 million 1 Mton hydrogen bombs.
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We place constraints on the formation redshifts for blue globular clusters (BGCs), independent of the details of hydrodynamics and population III star formation. The observed radial distribution of BGCs in the Milky Way Galaxy suggests that they formed in biased dark matter halos at high redshift. As a result, simulations of a ~1 Mpc box up to z ~ 10 must resolve BGC formation in LambdaCDM. We find that most halo stars could be produced from destroyed BGCs and other low-mass clusters that formed at high redshift. We present a proof-of-concept simulation that captures the formation of globular-like star clusters.
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This paper examines the possibilities of detecting hard gamma rays produced by the quantum-mechanical decay of small black holes created by inhomogeneities in the early universe. Observations of the isotropic gamma-ray background around 100 MeV place an upper limit of 10,000 per cu pc on the average number density of primordial black holes with initial masses around 10 to the 15th power g. The local number density could be greater than this by a factor of up to 1 million if the black holes were clustered in the halos of galaxies. The best prospect for detecting a primordial black hole seems to be to look for the burst of hard gamma rays that would be expected in the final stages of the evaporation of the black hole. Such observations would be a great confirmation of general relativity and quantum theory and would provide information about the early universe and about strong-interaction physics.
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The authors present a theory for the origin of globular clusters during the collapse of a protogalaxy. A thermal instability promotes the development of a two-phase structure in the gas when the cooling time is comparable to the free-fall time. The hot component, which remains near the virial temperature, compresses the cold component into discrete clouds with temperatures near 104K and mean densities in the range 1 - 10 M_sun;pc-3. It is shown that the initial amplitudes of the perturbations required to produce such clouds are of order 10%. When the abundance of heavy elements is less than 10-2Z_sun;, further cooling is inefficient and the minimum mass for gravitational instability is of order 106M_sun;. The authors compare these predictions with the observed properties of globular clusters and find satisfactory agreement, especially if there is some mass loss.
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A cosmological model based on a set of simple and currently popular ideas, and on the assumption that the mass of the universe is dominated by weakly interacting matter with negligible primeval pressure, yields two characteristic scales, one of which might naturally be identified with galaxies, the other with globular star clusters. The globular clusters tend to form with extended dark halos. The possible role of such halos in accounting for observed globular cluster systematics and the possible observational tests for dark halos are discussed.
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It is proposed that at least some globular clusters are formed during the interaction or merger of galaxies in order to explain the disk population of clusters in the Galaxy, the young globulars in the Magellanic Clouds, the excess of clusters around ellipticals relative to spirals of the same luminosity, and the anomalously large globular cluster systems around some galaxies in the center of galaxy clusters. It is shown that, if all protospirals contain subgalactic clouds with a similar mass spectrum, the specific frequency of globular clusters around spirals will be constant. Extending the argument makes it possible to predict, for a given cosmological spectrum of density fluctuations, the number of globular clusters that form as a function of galactic mass. It is shown that this hypothesis is consistent with a number of current observations and possible tests of the model are described.
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Primordial black holes (PBHs) remain a dark matter (DM) candidate of the Standard Model of Particle Physics. Previously, we proposed a new method of constraining the remaining PBH DM mass range using microlensing of stars monitored by NASA's Kepler mission. We improve this analysis using a more accurate treatment of the population of the Kepler source stars, their variability, and limb darkening. We extend the theoretically detectable PBH DM mass range down to 2 × 10–10M ☉, two orders of magnitude below current limits and one-third order of magnitude below our previous estimate. We address how to extract the DM properties, such as mass and spatial distribution, if PBH microlensing events were detected. We correct an error in a well-known finite-source limb-darkening microlensing formula and also examine the effects of varying the light curve cadence on PBH DM detectability. We also introduce an approximation for estimating the predicted rate of detection per star as a function of the star's properties, thus allowing for selection of source stars in future missions, and extend our analysis to planned surveys, such as the Wide-Field Infrared Survey Telescope.
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Although the first millisecond pulsars (MSPs) were discovered 30 years ago we still do not understand all details of their formation process. Here, we present new results from Tauris, Langer & Kramer (2012) on the recycling scenario leading to radio MSPs with helium or carbon-oxygen white dwarf companions via evolution of low- and intermediate mass X-ray binaries (LMXBs, IMXBs). We discuss the location of the spin-up line in the (P,Pdot)-diagram and estimate the amount of accreted mass needed to obtain a given spin period and compare with observations. Finally, we constrain the true ages of observed recycled pulsars via calculated isochrones in the (P,Pdot)-diagram.
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By considering adiabatic contraction of the dark matter (DM) during star formation, we estimate the amount of DM trapped in stars at their birth. If the DM consists partly of primordial black holes (PBHs), they will be trapped together with the rest of the DM and will be finally inherited by a star compact remnant --- a white dwarf (WD) or a neutron star (NS), which they will destroy in a short time. Observations of WDs and NSs thus impose constraints on the abundance of PBH. We show that the best constraints come from WDs and NSs in globular clusters which exclude the DM consisting entirely of PBH in the mass range 1016g3×1022g10^{16}{\rm g} - 3\times 10^{22}{\rm g}, with the strongest constraint on the fraction ΩPBH/ΩDM102\Omega_{\rm PBH} /\Omega_{\rm DM}\lesssim 10^{-2} being in the range of PBH masses 1017g101810^{17}{\rm g} - 10^{18} g.
Article
The problem of the dark matter in the universe is reviewed. A short history of the subject is given, and several of the most obvious particle candidates for dark matter are identified. Particular focus is given to weakly interacting, massive particles (WIMPs) of which the lightest supersymmetric particle is an interesting special case and a usful template. The three detection methods: in particle accelerators, by direct detection of scattering in terrestrial detectors, and indirect detection of products from dark matter particle annihilation in the galactic halo, are discussed and their complementarity is explained. Direct detection experiments have revealed some possible indications of a dark matter signal, but the situation is quite confusing at the moment. Very recently, also indirect detection has entered a sensitivity region where some particle candidates could be detectable. Indeed, also here there are some (presently non-conclusive) indications of possible dark matter signals, like an interesting structure at 130 GeV gamma-ray energy found in publicly available data from the Fermi-LAT space detector. The future of the field will depend on whether WIMPs are indeed the dark matter, something that may realistically be probed in the next few years. If this exciting scenario turns out to be true, we can expect a host of other, complementary experiments in the coming decade. If it is not true, the time scale and methods for detection will be much more uncertain.
Article
We formulate the equations of equilibrium of neutron stars taking into account strong, weak, electromagnetic, and gravitational interactions within the framework of general relativity. The nuclear interactions are described by the exchange of the sigma, omega, and rho virtual mesons. The equilibrium conditions are given by our recently developed theoretical framework based on the Einstein-Maxwell-Thomas-Fermi equations along with the constancy of the general relativistic Fermi energies of particles, the "Klein potentials", throughout the configuration. The equations are solved numerically in the case of zero temperatures and for selected parametrization of the nuclear models. The solutions lead to a new structure of the star: a positively charged core at supranuclear densities surrounded by an electronic distribution of thickness /(mec)\sim \hbar/(m_e c) of opposite charge, as well as a neutral crust at lower densities. Inside the core there is a Coulomb potential well of depth mπc2/e\sim m_\pi c^2/e. The constancy of the Klein potentials in the transition from the core to the crust, impose the presence of an overcritical electric field (mπ/me)2Ec\sim (m_\pi/m_e)^2 E_c, the critical field being Ec=me2c3/(e)E_c=m^2_e c^3/(e \hbar). The electron chemical potential and the density decrease, in the boundary interface, until values μecrust<μecore\mu^{\rm crust}_e < \mu^{\rm core}_e and ρcrust<ρcore\rho_{\rm crust}<\rho_{\rm core}. For each central density, an entire family of core-crust interface boundaries and, correspondingly, an entire family of crusts with different mass and thickness, exist. The configuration with ρcrust=ρdrip4.3×1011\rho_{\rm crust}=\rho_{\rm drip}\sim 4.3\times 10^{11} g/cm3^3 separates neutron stars with and without inner crust. We present here the novel neutron star mass-radius for the case ρcrust=ρdrip\rho_{\rm crust}=\rho_{\rm drip} and compare and contrast it with the one obtained from the Tolman-Oppenheimer-Volkoff treatment.
Article
The aim of this paper is to present the case that stellar mass primordial black holes make up the dark matter component of the Universe. A near critical density of compact bodies implies that most lines of sight will be gravitationally microlensed, and the paper focuses on looking for the predicted effects on quasar brightness and spectral variations. These signatures of microlensing include the shape of the Fourier power spectrum of the light curves, near achromatic and statistically symmetric variations, and the absence of time dilation in the timescale of variability. For spectral changes, as the continuum varies there should be little corresponding change in the strength of the broad lines. In all these cases, the observations are found to be consistent with the predictions for microlensing by a population of stellar mass compact bodies. For multiply lensed quasars where the images vary independently it is shown that stellar populations are too small to produce the observed microlensing effects, implying a population of compact dark matter bodies of around a stellar mass along the line of sight. The most serious objection to dark matter in the form of compact bodies has come from observations of microlensing of stars in the Magellanic Clouds. In this paper the expected event rate is re-analysed using more recent values for the structure and dynamics of the Galactic halo, and it is shown that there is then no conflict with the observations. Finally, the possible identity of a near critical density of dark matter in the form of stellar mass compact bodies is reviewed, with the conclusion that by far the most plausible candidates are primordial black holes formed during the QCD epoch. The overall conclusion of the paper is that primordial black holes should be seen alongside elementary particles as viable dark matter candidates.
Article
If the dark matter consists of primordial black holes (PBHs), we show that gravitational lensing of stars being monitored by NASA's Kepler search for extrasolar planets can cause significant numbers of detectable microlensing events. A search through the roughly 150,000 light curves would result in large numbers of detectable events for PBHs in the mass range 5×10(-10) M(⊙) to 10(-4) M(⊙). Nondetection of these events would close almost 2 orders of magnitude of the mass window for PBH dark matter. The microlensing rate is higher than previously noticed due to a combination of the exceptional photometric precision of the Kepler mission and the increase in cross section due to the large angular sizes of the relatively nearby Kepler field stars. We also present a new formalism for calculating optical depth and microlensing rates in the presence of large finite-source effects.
Article
We argue that a primordial black hole is a natural and unique candidate for all dark matter. We show that, in a smooth-hybrid new double inflation model, a right amount of the primordial black holes, with a sharply-defined mass, can be produced at the end of the smooth-hybrid regime, through preheating. We first consider masses < 10^(-7)M_sun which are allowed by all the previous constraints. We next discuss much heavier mass 10^5 M_sun hinted at by entropy, and galactic size evolution, arguments. Effects on the running of the scalar spectral index are computed.
Article
We update the constraints on the fraction of the Universe going into primordial black holes in the mass range 10^9--10^17 g associated with the effects of their evaporations on big bang nucleosynthesis and the extragalactic photon background. We include for the first time all the effects of quark and gluon emission by black holes on these constraints and account for the latest observational developments. We then discuss the other constraints in this mass range and show that these are weaker than the nucleosynthesis and photon background limits, apart from a small range 10^13--10^14 g, where the damping of cosmic microwave background anisotropies dominates. Finally we review the gravitational and astrophysical effects of nonevaporating primordial black holes, updating constraints over the broader mass range 1--10^50 g. Comment: 41 pages, 10 figures, REVTeX 4.1
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The Aquarius project is a very high-resolution simulation capable of resolving the full mass range of potential globular cluster (GC) formation sites. With a particle mass mp= 1.4 × 10⁴ M⊙, Aquarius yields more than 100 million particles within the virial radius of the central halo which has a mass of 1.8 × 10¹² M⊙, similar to that of the Milky Way. With this particle mass, dark matter concentrations (haloes) that give rise to GCs via our formation criteria contain a minimum of ∼2000 particles. Here, we use this simulation to test a model of metal-poor GC formation based on collapse physics. In our model, GCs form when the virial temperatures of haloes first exceed 10⁴ K as this is when electronic transitions allow the gas to cool efficiently. We calculate the ionizing flux from the stars in these first clusters and stop the formation of new clusters when all the baryonic gas of the Galaxy is ionized. This is achieved by adopting reasonable values for the star formation efficiencies and escape fraction of ionizing photons which result in similar numbers and masses of clusters to those found in the Milky Way. The model is successful in that it predicts ages (peak age ∼13.3 Gyr) and a spatial distribution of metal-poor GCs which are consistent with the observed populations in the Milky Way. The model also predicts that less than 5 per cent of GCs within a radius of 100 kpc have a surviving dark matter halo, but the more distant clusters are all found in dark matter concentrations. We then test a scenario of metal-rich cluster formation by examining mergers that trigger star formation within central gas discs. This results in younger (∼7–13.3 Gyr), more centrally located clusters (40 metal-rich GCs within 18 kpc from the centre of the host) which are consistent with the Galactic metal-rich population. We test an alternate model in which metal-rich GCs form in dwarf galaxies that become stripped as they merge with the main halo. This process is inconsistent with observed metal-rich globulars in the Milky Way because it predicts spatial distributions that are far too extended.
Article
We explore a mechanism for the formation of the first globular clusters, operating during the assembly of dwarf galaxies at high redshifts, z > 10. The substructure in the dark matter and the corresponding potential wells are responsible for setting the cluster scale of ~10^5 M_sun. The second mass scale in the formation problem, the stellar scale of ~1 M_sun, is determined in turn by the processes that cool the gas. We address the origin of the first, cluster scale by means of three-dimensional numerical simulations of the collapsing dark matter and gaseous components. We find that the gas falls into the deepest dark subhalos, resulting in a system of ~ 5 proto-globular clouds. The incipient globular clusters lose their individual dark halos in the process of violent relaxation, leading to the build-up of the general dark halo around the dwarf galaxy. Comment: 5 pages, 4 figures, accepted for publication in ApJ Letters
Article
In this review article, we discuss the current status of particle dark matter, including experimental evidence and theoretical motivations. We discuss a wide array of candidates for particle dark matter, but focus on neutralinos in models of supersymmetry and Kaluza-Klein dark matter in models of universal extra dimensions. We devote much of our attention to direct and indirect detection techniques, the constraints placed by these experiments and the reach of future experimental efforts. (C) 2004 Published by Elsevier B.V.
Article
We study the formation of globular clusters (GCs) in a Milky Way-size galaxy using a high-resolution cosmological simulation. The clusters in our model form in the dense cores of supergiant molecular clouds in the gaseous disks of high-redshift galaxies. The properties of clusters are estimated using a physically-motivated subgrid model of the isothermal cloud collapse. The first clusters in the simulation form at z ~ 12, while we conjecture that the best conditions for GC formation appear to be at z ~ 3-5. Most clusters form in the progenitor galaxies of the virial mass >10^9 Msun and the total mass of the cluster population is strongly correlated with the mass of its host galaxy with a fraction ~2x10^-4 of the galactic baryons being in the form of GCs. In addition, the mass of the GC population and the maximum cluster mass in a given region strongly correlate with the local average star formation rate. We find that the mass, size, and metallicity distributions of the cluster population identified in the simulation are remarkably similar to the corresponding distributions of the Milky Way globulars. We find no clear mass-metallicity or age-metallicity correlations for the old clusters. The zero-age cluster mass function can be approximated by a power-law, dN/dM ~ M^-alpha, with alpha ~ 2, in agreement with the mass function of young stellar clusters in starbursting galaxies. However, the shape of the zero-age mass function may be better described by the high-mass tail of a lognormal distribution which peaks at ~10^3 Msun. We discuss in detail the origin, universality, and dynamical evolution of the globular cluster mass function. Our results indicate that globular clusters with properties similar to those of observed clusters can form naturally within young dense gaseous disks at z >~ 3 in the LCDM cosmology.
Article
The detection of stars in the process of being tidally removed from globular clusters and dwarf spheroidals in the Galaxy's halo provides a strong constraint on their mass to light ratios and on the extent of their possible dark matter halos. If a significant dark matter component existed either within or beyond the observed stellar distribution, then stars would not be removed. We use numerical simulations to study mass loss from two component star clusters orbiting within a deeper potential. We find a global upper limit on the mass to light ratios of globular clusters, M/L \lsim 2.5, and rule out the possibility that they have extended halos of low luminosity material. Similarly, the tidal tails of dwarf spheroidals indicates that their dark matter halos must be truncated at \sim 400 pc therefore they have total mass to light ratios \lsim 100. Comment: 8 pages and 4 postscript figures, submitted to ApJL
Article
Globular cluster (GC) systems have now been studied in galaxies ranging from dwarfs to giants and spanning the full Hubble sequence of morphological types. Imaging and spectroscopy with the Hubble Space Telescope and large ground-based telescopes have together established that most galaxies have bimodal color distributions that reflect two subpopulations of old GCs: metal-poor and metal-rich. The characteristics of both subpopulations are correlated with those of their parent galaxies. We argue that metal-poor GCs formed in low-mass dark matter halos in the early universe and that their properties reflect biased galaxy assembly. The metal-rich GCs were born in the subsequent dissipational buildup of their parent galaxies and their ages and abundances indicate that most massive early-type galaxies formed the bulk of their stars at early times. Detailed studies of both subpopulations offer some of the strongest constraints on hierarchical galaxy formation that can be obtained in the near-field.
Article
We discuss the consequences of the accretion of dark matter (DM) particles on compact stars such as white dwarfs and neutron stars. We show that in large regions of the DM parameter space, these objects are sensitive probes of the presence of DM and can be used to set constraints both on the DM density and on the physical properties of DM particles.
Article
We investigate the effect of non-evaporating primordial black holes (PBHs) on the ionization and thermal history of the universe. X-rays emitted by gas accretion onto PBHs modify the cosmic recombination history, producing measurable effects on the spectrum and anisotropies of the Cosmic Microwave Background (CMB). Using the third-year WMAP data and FIRAS data we improve existing upper limits on the abundance of PBHs with masses >0.1 Msun by several orders of magnitude. Fitting WMAP3 data with cosmological models that do not al