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Constraints on primordial black holes as dark matter candidates from star formation

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Abstract

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.

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... 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.
... If the total energy lost, ∆E tot , through the initial hyperbolic orbit is larger than the initial energy E i = 1 2 mv 2 i , the PBH will be stuck in a bound orbit and, excluding external forces, will eventually sink to the NS's center and consume it [40][41][42]. ...
... Given that the PBH velocity within the NS is much higher than the local thermal velocity of the neutrons, we treat them as static in the NS reference frame. In the limit v ≪ c s (PBH velocity much smaller then the sound speed), including relativistic effects, the rate of mass capture for a PBH with speed v (with associated Lorentz factor γ) in a perfect fluid at equilibrium with density ρ and pressure P is [47] m = π d 2 c (ρ + P ) γ v , (2.11) where d c is the critical impact parameter for a Schwarzschild black hole at the local PBH velocity, which is given by solving the set of equations [40] ...
... This will also cause a force on the PBH, known as dynamical friction. In the NS reference frame, the change in momentum of a deflected neutron reads [40] ...
Article
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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.
... 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]. ...
... The escape velocity can be estimated from the baryonic density 0 and radius 0 of the cloud. These parameters are known from observations [25] and are summarized in Ref. [9]. For example, for a star of 1 ⊙ the values are 0 = 4300 AU and 0 = 10 6 GeV/cm 3 . ...
... Such simulations have been performed in Refs. [9,10,11]. The calculation is greatly simplified by the fact that the total dark matter mass on bound orbits is by many orders of magnitude smaller than the star mass, so one can simulate PBH trajectories one by one in the same gravitational potential of the contracting cloud, each time with different initial conditions. ...
Preprint
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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.
... One aspect of this scientific interest is related to dark matter and there is an exciting theory that PBHs could constitute dark matter (Ivanov et al. 1994, Carr et al. 2016b). Observations of the cosmic microwave background (CMB) implies that dark matter comprises 23% of the total amount of energy in the universe compared to 4% which is the contribution from baryonic matter (Capela et al. 2013a). There is much speculation regarding this theory as definitive evidence proving the existence of PBHs has yet to be found. ...
... II and in Sec. III I review the capture of PBHs by compact stars -more specifically neutron stars -both of these analyses yield constraints on the fraction of dark matter that could be in PBHs (Capela et al. 2013a, Capela et al. 2013b). In Sec. ...
... In their paper, Capela et al. (2013a) study the capture and adiabatic contraction of dark matter during star formation. Stars form from overdense regions of molecular gas found within giant molecular clouds (GMCs) which are extremely large (5 to 200 parsecs in diameter) and contain a huge amount of mass -roughly ! to ! . ...
Preprint
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The capture of dark matter by pre-stellar cores is considered, subsequently the dark matter will be trapped inside the compact remnant that the star becomes. If the dark matter is made up of primordial black holes (PBHs) then these will rapidly destroy the compact remnant and so constraints on the abundance of PBHs are implied by observations of compact remnants. Observational constraints based on black hole evaporation and gravitational lensing, as well as various dynamical constraints, are all considered and applied to the three allowed PBH mass ranges in which they could comprise the dark matter
... We consider that these low-mass stars acquired a quantity of bound DM at birth owing to adiabatic contraction during the collapse of the gas cloud that formed the star (Capela et al. 2013a ), which thereafter remains bound to the star for an arbitrarily long time. In other words, we assume that the original DM that is left bound to the star is not remo v ed by tidal disruption at a later time; we will discuss this further when considering the impact of external tides. ...
... In this paper, we will consider only the capture of this bound DM, and ne glect an y unbound DM that may be also be captured by the star when traversing it, if the incoming velocity is low enough to allow capture after a single passage through the star. From Abramowicz et al. ( 2009 ) and Capela et al. ( 2013a ) we expect the total capture rate should generally be dominated by this originally bound DM, especially when taking into account the effects of likely external perturbations on the DM orbits around the star that can randomly change orbital eccentricities. We compute the DM phase-space density in our model using σ h ( R ) from equation (13) of Łokas & Mamon ( 2001 ), for the isotropic case. ...
... As in previous work (e.g. Capela et al. 2013a ), we assume the orbital energy loss at each crossing of the stellar interior, | u | , is small compared to | u | , so we can integrate the evolution of the orbital energy with time t with the simple equation ...
Article
Primordial black holes in the asteroid-mass window, which might constitute all the dark matter, can be captured by stars when they traverse them at low enough velocity. After being placed on a bound orbit during star formation, they can repeatedly cross the star if the orbit happens to be highly eccentric, slow down by dynamical friction, and end up in the stellar core. The rate of these captures is highest in haloes of high dark matter density and low velocity dispersion, when the first stars form at redshift z ∼ 20. We compute this capture rate for low-metallicity stars of 0.3–1M1\, {\rm M_{\odot }}, and find that a high fraction of these stars formed in the first dwarf galaxies would capture a primordial black hole, which would then grow by accretion up to a mass that may be close to the total star mass. We show the capture rate of primordial black holes does not depend on their mass over this asteroid-mass window, and should not be much affected by external tidal perturbations. These low-mass stellar black holes could be discovered today in low-metallicity, old binary systems in the Milky Way containing a surviving low-mass main-sequence star or a white dwarf, or via gravitational waves emitted in a merger with another compact object. No mechanisms in standard stellar evolution theory are known to form black holes below the Chandrasekhar mass, so detecting a low-mass black hole would fundamentally impact our understanding of stellar evolution, dark matter, and the early Universe.
... PBH capture in the present Universe was reexamined by Capela et al. (2013a), considering star formation in globular clusters formed in dense DM halos made of PBHs in the asteroid-mass range. The impact of eccentric orbits to the capture rate was included in Capela et al. (2014), who found an enhanced capture rate implying that no neutron stars would form because all their progenitors would have captured a PBH that would accrete the star before or during the formation of the neutron star. ...
... We consider that these low-mass stars acquired a quantity of bound DM at birth owing to adiabatic contraction during the collapse of the gas cloud that formed the star (Capela et al. 2013a), which thereafter remains bound to the star for an arbitrarily long time. In other words, we assume that the original DM that is left bound to the star is not removed by tidal disruption at a later time; we will discuss this further when considering the impact of external tides. ...
... In this paper we will consider only the capture of this bound DM, and neglect any unbound DM that may be also be captured by the star when traversing it, if the incoming velocity is low enough to allow capture after a single passage through the star. From Abramowicz et al. (2009);Capela et al. (2013a) we expect the total capture rate should generally be dominated by this originally bound DM, especially when taking into account the effects of likely external perturbations on the DM orbits around the star that can randomly change orbital eccentricities. We compute the DM phase-space density in our model using ℎ ( ) from equation (13) of Łokas & Mamon (2001), for the isotropic case. ...
Preprint
Full-text available
Primordial black holes in the asteroid-mass window (1016\sim 10^{-16} to 1011M10^{-11} \rm M_{\odot}), which might constitute all the dark matter, can be captured by stars when they traverse them at low enough velocity. After being placed on a bound orbit during star formation, they can repeatedly cross the star if the orbit happens to be highly eccentric, slow down by dynamical friction and end up in the stellar core. The rate of these captures is highest in halos of high dark matter density and low velocity dispersion, when the first stars form at redshift z20z \sim 20. We compute this capture rate for low-metallicity stars of 0.3 to 1M1\rm M_{\odot}, and find that a high fraction of these stars formed in the first dwarf galaxies would capture a primordial black hole, which would then grow by accretion up to a mass that may be close to the total star mass. We show the capture rate of primordial black holes does not depend on their mass over this asteroid-mass window, and should not be much affected by external tidal perturbations. These low-mass stellar black holes could be discovered today in low-metallicity, old binary systems in the Milky Way containing a surviving low-mass main-sequence star or a white dwarf, or via gravitational waves emitted in a merger with another compact object. No mechanisms in standard stellar evolution theory are known to form black holes of less than a Chandrasekhar mass, so detecting a low-mass black hole would fundamentally impact our understanding of stellar evolution, dark matter and the early Universe.
... This mechanism has been considered in detail by ref. [70] for its effects on the population of luminous evaporating black holes captured around stars, and more recently by refs. [71][72][73] in the context of stellar destruction. Following ref. [71], a gas cloud of density ρ g and radius R g captures a DM halo with density of order ...
... [71][72][73] in the context of stellar destruction. Following ref. [71], a gas cloud of density ρ g and radius R g captures a DM halo with density of order ...
... This is mainly due to the sharp dependence on the velocity dispersion v 0 : if the system under consideration forms in a small DM substructure with a small dispersion, then the bound density can be considerable. In particular, in globular clusters, constraints can be derived from the absence of stellar destruction, as in ref. [71]. However, for a generic stellar system, capture due to adiabatic contraction is negligible. ...
Preprint
The vast datasets associated with extrasolar systems promise to offer sensitive probes of new physics in the near future. We consider the possibility that such systems may capture primordial black holes (PBHs) or other exotic compact objects, giving rise to unique observational signatures. We estimate the rate of captures by extrasolar systems, accounting for several distinct mechanisms. We find that the capture rate is negligible unless PBHs account for the entirety of dark matter in a narrow mass range just above the threshold of existing constraints from evaporation. In this scenario, luminous evaporating PBHs may be detectable by exoplanet searches.
... We summarise here this mechanism following Refs. [25,26]. ...
... where ρ DM is the ambient DM density and its velocity distribution is assumed to be Gaussian with the characteristic velocityv. The gravitational potential in turn can be estimated in terms of the parameters of the pre-stellar core and is in the range 3 × 10 −12 -3 × 10 −11 for stellar masses 1 − 10 M [25]. In all cases, one has ρ bound /ρ DM 1. ...
... Combining the results of Refs. [25,26], one obtains the following estimates of the total mass of the DM that acquires orbits crossing the star and may eventually be captured, for two different star masses: ...
Article
Full-text available
Probing the existence of hypothetical particles beyond the Standard model often deals with extreme parameters: large energies, tiny cross-sections, large time scales, etc. Sometimes, laboratory experiments can test required regions of parameter space, but more often natural limitations lead to poorly restrictive upper limits. In such cases, astrophysical studies can help to expand the range of values significantly. Among astronomical sources, used in interests of fundamental physics, compact objects—neutron stars and white dwarfs—play a leading role. We review several aspects of astroparticle physics studies related to observations and properties of these celestial bodies. Dark matter particles can be collected inside compact objects resulting in additional heating or collapse. We summarize regimes and rates of particle capturing as well as possible astrophysical consequences. Then, we focus on a particular type of hypothetical particles—axions. Their existence can be uncovered due to observations of emission originated due to the Primakoff process in magnetospheres of neutron stars or white dwarfs. Alternatively, they can contribute to the cooling of these compact objects. We present results in these areas, including upper limits based on recent observations.
... We summarise here this mechanism following Refs. [25,26]. ...
... where ρ DM is the ambient DM density and its velocity distribution is assumed to be Gaussian with the characteristic velocityv. The gravitational potential in turn can be estimated in terms of the parameters of the pre-stellar core and is in the range 3 × 10 −12 − 3 × 10 −11 for stellar masses 1 − 10 M [25]. In all cases one has ρ bound /ρ DM 1. ...
... Combining the results of Refs. [25,26] one obtains the following estimates of the total mass of the DM that acquires orbits crossing the star and may eventually be captured, for two different star masses: ...
Preprint
Full-text available
Probing the existence of hypothetical particles beyond the Standard model often deals with extreme parameters: large energies, tiny cross-sections, large time scales, etc. Sometimes laboratory experiments can test required regions of parameter space, but more often natural limitations leads to poorly restrictive upper limits. In such cases astrophysical studies can help to expand the range of values significantly. Among astronomical sources, used in interests of fundamental physics, compact objects -- neutron stars and white dwarfs, -- play a leading role. We review several aspects of astroparticle physics studies related to observations and properties of these celestial bodies. Dark matter particles can be collected inside compact objects resulting in additional heating or collapse. We summarize regimes and rates of particle capturing as well as possible astrophysical consequences. Then we focus on a particular type of hypothetical particles -- axions. Their existence can be uncovered due to observations of emission originated due to Primakoff process in magnetospheres of neutron stars or white dwarfs. Alternatively, they can contribute to cooling of these compact objects. We present results in these areas, including upper limits based on recent observations.
... While it is hard for astrophysical BHs to form with one or two solar masses, a PBH can form with a NS or solar mass [23][24][25][26][27][28]; the detection of sub-Chandrasekhar mass black hole mergers would unmistakably lead to the discovery of this class of exotic compact objects [11,29,30]. PBHs can have various effects on astrophysical objects, including the formation of bound states with other PBHs [31], or the implosion of JCAP10(2021)019 compact objects into low-mass BHs [9,32,33] which otherwise would rarely exist through standard BH formation channels. ...
... An interesting mass range to consider for the PBH is 10 −15 to 10 −8 solar mass, as discussed in [32,[59][60][61][62]. The radius of the PBH is about r ∼ 10 −8 cm (m pbh /10 −13 m ). ...
... The radius of the PBH is about r ∼ 10 −8 cm (m pbh /10 −13 m ). They have been considered to be captured by or to destroy white dwarfs (WD) [63] and neutron stars [32]. The potential constraints set by these considerations are sensitive to the assumptions of the properties of each astrophysical systems, which have large observational uncertainties [64][65][66][67][68]. ...
Article
Full-text available
We investigate the possibility of the gravitational-wave event GW170817 being a light, solar-mass black hole (BH) — neutron star (NS) merger. We explore two exotic scenarios involving primordial black holes (PBH) that could produce such an event, taking into account available observational information on NGC 4993. First, we entertain the possibility of dynamical NS-PBH binary formation where a solar-mass PBH and a NS form a binary through gravitational interaction. We find that while dynamical NS-PBH formation could account for the GW170817 event, the rate is highly dependent on unknown density contrast factors and could potentially be affected by galaxy mergers. We also find that PBH-PBH binaries would likely have a larger merger rate, assuming the density contrast boost factor of an order similar to the NS-PBH case. These exotic merger formations could provide new channels to account for the volumetric rate of compact-object mergers reported by LIGO/Virgo. Secondly, we consider the case where one of the NS's in a binary NS system is imploded by a microscopic PBH. We find that the predicted rate for NS implosion into a BH is very small, at least for the specific environment of NGC 4993. We discuss how our analysis can be applied to similar existing (GW190425 and GW190814) and future observations.
... Montero-Camacho et al. (2019) have found that the probabilities of capture by a star are low, as a PBH on average falls in faster than the stellar escape velocity and hence transits the star with only negligible dissipation from dynamical friction and accretion. The capture of PBHs during star formation is much more likely due to the time-dependent gravitational potential of the adiabatically collapsing cloud (Capela et al. 2013(Capela et al. , 2014Eroshenko 2023). PBH capture in a star-forming region is even more likely in dwarf galaxies due to their lower mean velocities as well as in the early Universe, which has formed the basis for additional observational constraints on PBH dark matter (Oncins et al. 2022;Esser & Tinyakov 2023). ...
... In contrast, capture during star formation is made possible by the time-dependent gravitational potential of the collapsing cloud. During collapse, a PBH present in the cloud is not accelerated by the gas around it, and so it can become bound to the cloud (Capela et al. 2013(Capela et al. , 2014. This capture mechanism depends on the PBH velocity distribution, with only those PBHs in the slow end of the tail being captured. ...
Article
Full-text available
Hawking proposed that the Sun may harbor a primordial black hole (BH) whose accretion supplies some of the solar luminosity. Such an object would have formed within the first 1 s after the Big Bang with the mass of a moon or an asteroid. These light BHs are a candidate solution to the dark matter problem, and could grow to become stellar-mass BHs if captured by stars. Here we compute the evolution of stars having such a BH at their center. We find that such objects can be surprisingly long-lived, with the lightest BHs having no influence over stellar evolution, while more massive ones consume the star over time to produce a range of observable consequences. Models of the Sun born about a BH whose mass has since grown to approximately 10 ⁻⁶ M ⊙ are compatible with current observations. In this scenario, the Sun would first dim to half its current luminosity over a span of 100 Myr as the accretion starts to generate enough energy to quench nuclear reactions. The Sun would then expand into a fully convective star, where it would shine luminously for potentially several gigayears with an enriched surface helium abundance, first as a sub-subgiant star, and later as a red straggler, before becoming a subsolar-mass BH. We also present results for a range of stellar masses and metallicities. The unique internal structures of stars harboring BHs may make it possible for asteroseismology to discover them, should they exist. We conclude with a list of open problems and predictions.
... Another possibility is a gravitational trapping of the DM during formation of the neutron star [40,41]. The latter objects are created in the supernova collapses of ordinary stars with masses above ∼9 M ⊙ , which, in turn, are born in giant molecular clouds. ...
... Eventually, this DM ends up in the center of a heavy progenitor star; estimates of Refs. [40,41] show that the captured DM mass is close to Eqs. (5) and (6) within an order of magnitude. Later, a fraction of the star DM is inherited by the neutron star in the course of supernova collapse. ...
Article
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Black holes with masses ≈1 M⊙ cannot be produced via stellar evolution. A popular scenario of their formation involves transmutation of neutron stars—by accumulation of dark matter triggering gravitational collapse in the star centers. We show that this scenario can be realized in the models of bosonic dark matter despite the apparently contradicting requirements on the interactions of dark matter particles: on the one hand, they should couple to neutrons strongly enough to be captured inside the neutron stars, and on the other, their loop-induced self-interactions impede collapse. Observing that these conflicting conditions are imposed at different scales, we demonstrate that models with efficient accumulation of dark matter can be deformed at large fields to make unavoidable its subsequent collapse into a black hole. Workable examples include weakly coupled models with bent infinite valleys.
... Second, the collapse of the gas cloud into a more compact star leads to the adiabatic contraction of gravitationally bound population of the dark clouds. If the latter contribution to the total mass was subdominant, then a rather spiky profile would have been formed, n(r) ∼ r −3/2 (Capela et al., 2013). In this case the total number of clouds grows with a radius much slower, N ∼ r 3/2 , not N ∼ r 3 and total number of bound clouds and their total mass would be constrained much stronger: ...
Preprint
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Several observational lines of evidence imply that a fraction of the dark matter in the Galaxy may be comprised of small cold clouds of molecular hydrogen. Such objects are difficult to detect because of their small size and low temperature, but they can reveal themselves with gamma radiation arising in interactions between such clouds and cosmic rays or as dark shadows cast on the optical, UV and X-ray sky background. In our work we use the data of Fermi LAT 4FGL-DR4 catalogue of gamma-ray sources together with the data of GALEX UV All-Sky Survey to search for small dark clouds of molecular hydrogen in the Solar neighbourhood. This approach allows us to put an upper limit on the local concentration of such objects: n<2.2×1011AU3n < 2.2 \times 10^{-11} {\mathrm{AU}^{-3}}. Constraints (upper limits) on the total amount of matter in this form bound to the Sun strongly depend on the radial profile of the clouds' distribution and reside in 0.0530 M0.05-30~M_{\odot} mass range.
... 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
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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
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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.
... 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.
... 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.
... 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.
... Hawking (1971) provided the first order-of-magnitude estimate for the stellar PBH capture rate, suggesting that a PBH of ∼ 10 17 g could be captured by a Sun-like star. Capela et al. (2013) considered capture rates in globular clusters and the survival of white dwarfs and neutron stars as a potential constraint on PBHs. Oncins et al. (2022) also considered capture in early, low-metallicity dwarf galaxies, finding the rate is largely insensitive to the PBH mass in the asteroid-mass window, and that many early stars could have been transmuted to sub-solar mass black holes. ...
Preprint
Presently, primordial black holes (PBHs) in the asteroid-mass window from 101610^{-16} M_\odot to 101010^{-10} M_\odot are a popular dark matter candidate. If they exist, some stars would capture them upon formation, and they would slowly accrete the star over gigayears. Such Hawking stars -- stars with a central PBH -- provide a novel channel for the formation of both sub-Chandrasekhar mass black holes as well as red straggler stars. Here we report on stellar evolution models that extend our previous work to Hawking stars with masses between 0.5 and 1.4 M_\odot. We explore three accretion schemes, and find that a wide range of PBHs in the asteroid-mass window can robustly accrete stars as small as 1 M_{\odot} within the age of the Universe. This mechanism of producing sub-solar mass black holes is highly dependent on the assumed accretion physics and stellar metallicity. Lower-metallicity stars are generally accreted more rapidly, suggesting that it may be more likely for sub-Chandrasekhar mass Hawking stars formed in the early universe, such as those in ultra-faint dwarf (UFD) galaxies, to transmute their star into a sub-Chandrasekhar mass black hole within a Hubble time. We present a stellar population synthesis of a Draco II-like UFD galaxy containing Hawking stars and show that the number of red stragglers they produce can qualitatively match the observed population.
... Other constraints on PBHs in this mass range have been claimed in Refs. [52,53], but Ref. [16] showed that current modeling and astrophysical uncertainties do not support the robustness of those bounds. ...
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Recent surveys have discovered a population of faint supernovae, known as Ca-rich gap transients, inferred to originate from explosive ignitions of white dwarfs. In addition to their unique spectra and luminosities, these supernovae have an unusual spatial distribution and are predominantly found at large distances from their presumed host galaxies. We show that the locations of Ca-rich gap transients are well matched to the distribution of dwarf spheroidal galaxies surrounding large galaxies, in a scenario where dark matter interactions induce thermonuclear explosions among low-mass white dwarfs that may be otherwise difficult to ignite with standard stellar or binary evolution mechanisms. A plausible candidate to explain the observed event rate are primordial black holes with masses above 10 21 grams. Published by the American Physical Society 2024
... However, PBHs in the intermediate mass range 10 17 -10 23 g (often refereed to as asteroid-mass PBHs) are very poorly constrained (for various efforts, see Refs. [22][23][24][25][26][27][28][29][30][31][32]). Therefore, in this mass range, PBHs can constitute the whole of DM, see Fig. 1. ...
Article
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Primordial black holes (PBHs) in the mass range ∼ 10 17 – 10 23 g are currently unconstrained, and can constitute the full dark matter (DM) density of the universe. Motivated by this, in the current work, we aim to relate the existence of PBHs in the said mass range to the production of observable gravitational waves (GWs) in the upcoming GW detectors. We follow a relatively model-independent approach assuming that the PBHs took birth in a radiation dominated era from enhanced primordial curvature perturbation at small scales produced by inflation. We show that the constraints from cosmic microwave background and BAO data allow for the possibility of PBHs being the whole of DM density of the universe. Finally, we derive the GW spectrum induced by the enhanced curvature perturbations and show that they are detectable in the future GW detectors like eLISA, LISA, BBO, and DECIGO. Published by the American Physical Society 2024
... The problem of capture during star formation is hard, but past authors have considered it and shown that it could be quite likely in lower mass halos with slower velocity distributions, especially those found in dwarf galaxies or possibly the early universe . Indeed, arguments are now abundant in the literature showing that if asteroid-mass PBHs exist in large numbers then one should necessarily expect a few to be captured by stars (Capela et al. 2013(Capela et al. , 2014Montero-Camacho et al. 2019). ...
Article
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There is probably not a black hole in the center of the Sun. Despite this detail, our goal in this work to convince the reader that this question is interesting and that work studying stars with central black holes is well motivated. If primordial black holes exist then they may exist in sufficiently large numbers to explain the dark matter in the universe. While primordial black holes may form at almost any mass, the asteroid-mass window between 10−16−10−10M⊙10161010 M10^{-16} - 10^{-10}\ \textrm{M}_{\odot } remains a viable dark matter candidate and these black holes could be captured by stars upon formation. Such a star, partially powered by accretion luminosity from a microscopic black hole in its core, has been called a ‘Hawking star.’ Stellar evolution of Hawking stars is highly nontrivial and requires detailed stellar evolution models, which were developed in our recent work. We present here full evolutionary models of solar mass Hawking stars using two accretion schemes: one with a constant radiative efficiency, and one that is new in this work that uses an adaptive radiative efficiency to model the effects of photon trapping.
... Observationally, this effect would manifest itself as the disappearance of stars, since the resulting sub-solar mass black holes are basically invisible. This process has been considered in application to neutron stars and white dwarfs by Capela et al. (2013aCapela et al. ( ,b, 2014 and to main-sequence stars by Esser & Tinyakov (2023). The advantage of the latter as PBH detectors is that they themselves are much easier to observe. ...
Article
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If primordial black holes constitute the dark matter, stars forming in dark-matter dominated environments with low velocity dispersions, such as ultra-faint dwarf galaxies, may capture a black hole at birth. The capture probability is non-negligible for primordial black holes of masses around 1020 g, and increases with stellar mass. Moreover, infected stars are turned into virtually invisible black holes on cosmologically short timescales. Hence, the number of observed massive main-sequence stars in ultra-faint dwarfs should be suppressed if the dark matter was made of asteroid-mass primordial black holes. This would impact the measured mass distribution of stars, making it top-light (i.e. depleted in the high-mass range). Using simulated data that mimic the present-day observational power of telescopes, we show that already existing measurements of the mass function of stars in local ultra-faint dwarfs could be used to constrain the fraction of dark matter composed of primordial black holes in the – currently unconstrained – mass range of 1019 − 1021 g.
... Besides gravitational waves, there are multiple ways through which PBHs could manifest themselves. These depends on their mass ranges, and might for instance be due to cosmic microwave background distortions induced by accretion onto the PBHs [214, 216, 353-356, 358-361, 497, 498], various dynamical effects [23,351,[499][500][501][502][503], X-Ray/infrared backgrounds [22,223,504,505], gravitational lensing [18,20,39,40,337,[506][507][508][509][510][511][512][513][514][515][516][517][518], or bursts from disruptive events, such as neutron stars [519] or white dwarfs [520] (cf. also Reference [25] for an extended recent discussion on positive evidence for PBHs). ...
Preprint
We review aspect of primordial black holes, i.e., black holes which have been formed in the early Universe. Special emphasis is put on their formation, their r\^ole as dark matter candidates and their manifold signatures, particularly through gravitational waves.
... Throughout this paper, we will set the units = c = 1 unless otherwise specified. 1 Although there have been other constraints discussed in this mass range such as the femtolensing events of γ-ray bursts [18], the dynamical capture of PBHs by stars [19][20][21][22], and the ignition of white dwarfs by PBHs [23]. However, recent studies have revisited these constraints and claimed that this mass window remains open for PBHs as dark matter candidates [24,25]. ...
Article
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Antisymmetric tensor field (two-form field) is a ubiquitous component in string theory and generally couples to the scalar sector through its kinetic term. In this paper, we propose a cosmological scenario that the particle production of two-form field, which is triggered by the background motion of the coupled inflaton field, occurs at the intermediate stage of inflation and generates the sizable amount of primordial black holes as dark matter after inflation. We also compute the secondary gravitational waves sourced by the curvature perturbation and show that the resultant power spectra are testable with the future space-based laser interferometers.
... This mechanism has been considered in detail by ref. [72] for its effects on the population of luminous evaporating black holes captured around stars, and more recently by refs. [73][74][75] in the context of stellar destruction. Following ref. [73], a gas cloud of density ρ g and radius R g captures a DM halo with density of order ...
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The vast datasets associated with extrasolar systems promise to offer sensitive probes of new physics in the near future. We consider the possibility that such systems may capture primordial black holes (PBHs) or other exotic compact objects, giving rise to unique observational signatures. We estimate the rate of captures by extrasolar systems, accounting for several distinct mechanisms. We find that the capture rate is negligible unless PBHs account for the entirety of dark matter in a narrow mass range just above the threshold of existing constraints from evaporation. In this scenario, luminous evaporating PBHs may be detectable by exoplanet searches.
... The possibility of PBH capture in the present Universe was reexamined by [173], considering star formation in globular clusters formed in dense dark matter halos made of PBHs in the asteroid mass range. If the star become a neutron star while it had a PBH within itself, the much higher densities of the object would result in an almost instant accretion by the PBH. ...
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Primordial black holes (PBHs) are a fascinating candidate for being the dark matter, albeit one which has been heavily constrained. This review presents an in depth look at those observational constraints, particularly at their nuances and uncertainties. Despite their varied origins, the standard PBH formation path is assumed to be collapse of perturbations after inflation, which should leave signals visible in the CMB at certain scales. Other constraints come from microlensing surveys, which severely limit PBHs as dark matter in the solar to satellite range, but there are diminishing results in regards to lower mass ranges. Gravitational waves signals and PBH evaporation from Hawking radiation also make for useful probes, but the former requires the next generation of experiments before making constraints beyond the solar mass range, and the later is severely limited above 1016M10^{-16} \rm M_{\odot}. Other dynamical and accretion constraints exist for PBH of large masses. Care also has to be given, as all these constraints can carry different implications coming from differences between monochromatic and extended mass distributions, and their degree of clustering. Beyond all these issues, a window still exists for primordial black holes to be all of the dark matter between 101610^{-16} and $10^{-11} \rm M_{\odot}
... Capela et al. have constrained PBHs by considering their capture by white dwarfs [129] or neutron stars [130] at the centres of globular clusters, while Pani and Loeb [131] have argued that this excludes them from providing the dark matter in the range 10 14 -10 17 g. However, these limits have been disputed [132] because the dark matter density in globular clusters is now known to be much lower than assumed in these analyses [133]. ...
Article
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We review the formation and evaporation of primordial black holes (PBHs) and their possible contribution to dark matter. Various constraints suggest they could only provide most of it in the mass windows 10^{17}\; 10 17 – 10^{23}\; 10 23 g or 10 10 – 10^2\;M_{\odot} 10 2 M ⊙ , with the last possibility perhaps being suggested by the LIGO/Virgo observations. However, PBHs could have important consequences even if they have a low cosmological density. Sufficiently large ones might generate cosmic structures and provide seeds for the supermassive black holes in galactic nuclei. Planck-mass relics of PBH evaporations or stupendously large black holes bigger than 10^{12}\;M_{\odot} 10 12 M ⊙ could also be an interesting dark component.
... 2. The blue band around m BH ∼ 10 −13 M indicates where the PBH abundance could account for all DM in the Universe. This region might be ruled out by observations of white dwarfs, neutron stars, and supernovae [381][382][383]. These constraints, drawn in light gray, are however currently being disputed [82]. ...
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Despite their tremendous successes, modern-day cosmology and particle physics harbor a variety of unresolved mysteries. Two of the biggest are the origin of the baryon asymmetry of the Universe and the existence and nature of dark matter. In the present thesis, the author addresses these topics in various ways. The first part of the thesis is concerned with cosmological first-order phase transitions that may have occurred shortly after the Big Bang. Such transitions proceed via the nucleation and expansion of true vacuum bubbles and give rise to a rich phenomenology. The author suggests a mechanism to simultaneously explain the baryon asymmetry and dark matter, based on the out-of-equilibrium dynamics at the boundary of a dark phase transition with large order parameter. The same class of phase transitions can, in the parameter regime of small dark matter Yukawa couplings, lead to the production of primordial black holes via the compression of the plasma in shrinking false vacuum regions, as the author demonstrates with a sophisticated numerical simulation. In a third project regarding cosmological phase transitions, the author investigates the possibility of sub-MeV hidden sectors that are decoupled from the remaining plasma and cold enough to be reconciled with cosmological constraints, but at the same time give rise to a detectable gravitational-wave spectrum produced during bubble collisions. In the second part of the thesis, the author assesses the prospects for new physics searches at the DUNE near detector, focusing on the DUNE-PRISM concept, which suggests consecutive measurements at different on- and off-axis positions. This setup achieves improved signal-to-background ratios and reduces systematic uncertainties.
... Capela et al. have constrained PBHs by considering their capture by white dwarfs [120] or neutron stars [121] at the centres of globular clusters, while Pani and Loeb [122] have argued that this excludes them from providing the dark matter in the range 10 17 -10 14 g. However, these limits have been disputed [123] because the dark matter density in globular clusters is now known to be much lower than assumed in these analyses [124]. ...
Preprint
We review the formation and evaporation of primordial black holes (PBHs) and their possible contribution to dark matter. Various constraints suggest they could only provide most of it in the mass windows 101710^{17} - 102310^{23}\,g or 10 - 102M10^{2}\,M_{\odot}, with the last possibility perhaps being suggested by the LIGO/Virgo observations. However, PBHs could have important consequences even if they have a low cosmological density. Sufficiently large ones might generate cosmic structures and provide seeds for the supermassive black holes in galactic nuclei. Planck-mass relics of PBH evaporations or stupendously large black holes bigger than 1012M10^{12}\,M_{\odot} could also be an interesting dark component.
... The PBHs, if massive enough to be stable on cosmological timescales, are a suitable DM candidate. This possibility, however, has been put under pressure from various considerations, including accretion and subsequent energy injection JCAP08(2020)045 into the CMB [13,14], lensing observations [15], and constraints from star formation [16], meaning much of the possible mass range is disfavoured [17]. Nevertheless, this remains an active area of research with many constraints having recently been either tightened or re-evaluated entirely [18][19][20]. ...
Article
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Dark matter coupled solely gravitationally can be produced through the decay of primordial black holes in the early universe. If the dark matter is lighter than the initial black hole temperature, it could be warm enough to be subject to structure formation constraints. In this paper we perform a more precise determination of these constraints. We first evaluate the dark matter phase-space distribution, without relying on the instantaneous decay approximation. We then interface this phase-space distribution with the Boltzmann code to extract the corresponding matter power spectrum, which we find to match closely those of warm dark matter models, albeit with a different dark matter mass. This mapping allows us to extract constraints from Lyman-α data without the need to perform hydrodynamical simulations. We robustly rule out the possibility, consistent with previous analytic estimates, of primordial black holes having come to dominate the energy density of the universe and simultaneously given rise to all the DM through their decay. Consequences and implications for dark radiation and leptogenesis are also briefly discussed.
... We note that, instead of the Ω PBH , we write the β(M ) values, see Eq. (27), since PBH with mass M 10 15 grams have already evaporated. 6 In that range there are feeble constraints coming from white dwarfs and neutron stars [82][83][84][85] but these constraints, together with others in the same mass range such as femtolensing and picolensing, are seen as insecure [16,86]. Fig.4. ...
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There is a growing expectation that the gravitational wave detectors will start probing the stochastic gravitational wave backgrounds in the following years. We explore the spectral shapes of gravitational waves induced to second order by scalar perturbations and presumably have been produced in the early universe. We calculate the gravitational wave spectra generated during radiation and kination eras together with the associated primordial black hole counterpart. We employ power spectra for the primordial curvature perturbation generated by α\alpha-attractors and non-minimal derivative coupling inflation models as well as Gaussian and delta-type shapes. We demonstrate the ability of the tensor modes to constrain the spectrum of the primordial curvature perturbations and discriminate among inflationary models. Gravitational wave production during kination and radiation era can also be distinguished by their spectral shapes and amplitudes.
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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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Axion stars could form binaries with neutron stars. Given the extremely strong external magnetic field exhibited by individual neutron stars, there can be a substantial conversion of axions to photons in these binaries. The photon emission is doubly modulated due to the neutron star spinning and the axion star orbiting, yielding a unique discovery signal. Similar features are also generated in binaries between a neutron star and an axion-clouded black hole. Encouragingly, such binaries are found to be within the reach of ongoing and upcoming experiments (e.g., the Five-hundred-meter Aperture Spherical Telescope and the future Square Kilometer Array) for certain parameter regions. They thus provide a promising astronomical laboratory for detecting axions and axion dark matter.
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In this paper, we examine whether low-mass Primordial Black Holes (PBHs) can be considered a plausible dark matter candidate in galactic halos. We derive the relativistic dynamics of PBHs around the heavy compact objects and evaluate their collision rate, as well as the likelihood of PBH capture in neutron stars and black holes. Although the rate of these collisions in the Milky Way is lower than our lifetime (i.e. almost one collision per hundred years), it may still be observable on cosmological scales. Additionally, we investigate the gravitational wave emission as an important observable window for PBH-astrophysical black hole merging. For the allowed range of PBH mass, gravitational wave signal is smaller than the sensitivity of present gravitational wave detectors. We provide observational prospect for detection of these events in future.
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Primordial black holes, which could have formed during the early Universe through overdensities in primordial density fluctuations during inflation, are potential candidates for dark matter. We explore the use of lensing parallax of Gamma ray bursts (GRBs), which results in different fluxes being observed from two different vantage points, in order to probe the abundance of primordial black holes in the unexplored window within the mass range [10−15–10−11] M⊙. We derive the optical depth for the lensing of GRBs with a distribution of source properties and realistic detector sensitivities. We comment on the ability of the proposed Indian twin satellite mission Daksha in its low earth orbit to conduct this experiment. If the two Daksha satellites observe 10000 GRBs simultaneously and the entirety of dark matter is made up of [10−15–10−12] M⊙ black holes, Daksha will detect non-zero lensing events with a probability ranging from 80 to 50 per cent at the bin edges, respectively. Non-detections will not conclusively rule out primordial black holes as dark matter in this mass range. However, we show that meaningful constraints can be obtained in such a case if the two satellites are separated by at least the Earth-Moon distance.
Preprint
Primordial black holes, which could have formed during the early Universe through overdensities in primordial density fluctuations during inflation, are potential candidates for dark matter. We explore the use of lensing parallax of Gamma ray bursts, which results in different fluxes being observed from two different vantage points, in order to probe the abundance of primordial black holes in the unexplored window within the mass range [10151011]M[10^{-15}-10^{-11}]M_\odot. We derive the optical depth for the detectability of lensing of GRBs with a distribution of source properties and realistic detector sensitivities. We comment on the ability of the proposed Indian twin satellite mission Daksha in its low earth orbit to conduct this experiment. If the two Daksha satellites observe 10000 GRBs simultaneously and the entirety of dark matter is made up of [10151012]M[10^{-15}-10^{-12}]M_\odot black holes, Daksha will detect non-zero lensing events with a probability ranging from [80, 50] per cent. Non-detections will not conclusively rule out primordial black holes as dark matter in this mass range. However, we show that meaningful constraints can be obtained in such a case if the two satellites are separated by at least the Earth-Moon distance.
Article
We propose a way to constrain the primordial black hole (PBH) abundance in the range of PBH masses m around 1020 g based on their capture by Sun-like stars in dwarf galaxies, with subsequent star destruction. We calculate numerically the probability of a PBH capture by a star at the time of its formation in an environment typical of dwarf galaxies. Requiring that no more than a fraction ξ of stars in a dwarf galaxy is destroyed by PBHs translates into an upper limit on the PBH abundance. For the parameters of Triangulum II and ξ=0.5, we find that no more than ∼35% of dark matter can consist of PBHs in the mass range 1018–(a few)×1021 g. The constraints depend strongly on the parameter ξ and may significantly improve if smaller values of ξ are established from observations. An accurate determination of ξ from dwarf galaxy modeling is thus of major importance.
Article
In this paper we propose a new way to detect sublunar-mass primordial black holes (PBHs) by direct observations of the Earth-Moon binary system. Our method is based on treating PBH as a perturbation term, by assuming that the PBH is sweeping across the Solar System with a sublunar mass and is far away from the Earth-Moon binary (much greater than 1 AU). This perturbation treatment allows us to develop a framework to calculate the orbits of a generic binary system such as the Earth-Moon binary system. Our numerical results show that the Earth-Moon distance is sensitive to the initial values of the system. In most cases, the long-duration interactions between the PBH and the Earth-Moon system can induce lasting imprints on the Earth-Moon’s orbit, and these imprints can accumulate over time, eventually giving rise to observable deviations which can be used to infer the properties of the PBH.
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Constraining the inflationary epoch is one of the aims of modern cosmology. In order to fully exploit current and future small-scale observations, it is necessary to devise tools to directly relate them to the early Universe’s dynamics. We present here a novel reverse engineering approach able to connect fundamental late-time observables to consistent inflationary dynamics and, eventually, to the inflaton potential. Employing this procedure, we are able to describe which conditions can give rise to a raised plateau in the power spectrum of curvature perturbations at small scales, which are not constrained by CMB observations. Within this new phenomenologically driven approach, we find that inflation can generate a raised plateau in the spectrum of curvature perturbations that potentially connects three fundamental observables; a dominant component of the dark matter in the form of asteroid-mass/atomic-size primordial black holes, detectable signals in stochastic gravitational waves, and a subdominant fraction of stellar-mass primordial black holes mergers.
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We update the constraints on the fraction of the Universe that may have gone into primordial black holes (PBHs) over the mass range 10 ⁻⁵ to 10 ⁵⁰ g. Those smaller than ∼10 ¹⁵ g would have evaporated by now due to Hawking radiation, so their abundance at formation is constrained by the effects of evaporated particles on big bang nucleosynthesis, the cosmic microwave background (CMB), the Galactic and extragalactic γ -ray and cosmic ray backgrounds and the possible generation of stable Planck mass relics. PBHs larger than ∼10 ¹⁵ g are subject to a variety of constraints associated with gravitational lensing, dynamical effects, influence on large-scale structure, accretion and gravitational waves. We discuss the constraints on both the initial collapse fraction and the current fraction of the dark matter (DM) in PBHs at each mass scale but stress that many of the constraints are associated with observational or theoretical uncertainties. We also consider indirect constraints associated with the amplitude of the primordial density fluctuations, such as second-order tensor perturbations and μ -distortions arising from the effect of acoustic reheating on the CMB, if PBHs are created from the high- σ peaks of nearly Gaussian fluctuations. Finally we discuss how the constraints are modified if the PBHs have an extended mass function, this being relevant if PBHs provide some combination of the DM, the LIGO/Virgo coalescences and the seeds for cosmic structure. Even if PBHs make a small contribution to the DM, they could play an important cosmological role and provide a unique probe of the early Universe.
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There is a growing expectation that the gravitational wave detectors will start probing the stochastic gravitational wave backgrounds in the following years. We explore the spectral shapes of gravitational waves induced to second order by scalar perturbations and presumably have been produced in the early Universe. We calculate the gravitational wave spectra generated during radiation and kination eras together with the associated primordial black hole counterpart. We employ power spectra for the primordial curvature perturbation generated by α-attractors and nonminimal derivative coupling inflation models as well as Gaussian and delta-type shapes. We demonstrate the ability of the tensor modes to constrain the spectrum of the primordial curvature perturbations and discriminate among inflationary models. Gravitational wave production during kination and radiation eras can also be distinguished by their spectral shapes and amplitudes.
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Primordial black holes (PBH), produced through a variety of processes in the early universe, could fill galactic halos accounting for a fraction or the totality of the dark matter. In particular, PBH with substellar masses could be captured by stars, start to swallow their material, and eventually turn them into BH, hence originating a peculiar new type of stellar catastrophic event. Here we revisit this process in the most favorable case of PBH capture by neutron stars. We detail a number of novel features in the capture phase, during the settling within the star and mass growth of the PBH, and illustrate some phenomenological consequences. In particular, we point out that in the subsonic regime the PBH drag takes the form of a Bondi accretion. As a result, the onset of the final transmutation of the NS into a stellar sized BH is expected with the PBH seed in slight off-center position. We also compute the gravitational wave energy-loss and signals associated to different phases of the PBH-stellar interaction. In particular, the emission associated to the accretion phase is periodic with a few kHz frequency; in the rare case of a nearby Galactic event and for light PBH, it could constitute a warning of the forthcoming transmutation.
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Although the dark matter is usually assumed to be made up of some form of elementary particle, primordial black holes (PBHs) could also provide some of it. However, various constraints restrict the possible mass windows to 10 ¹⁶ –10 ¹⁷ g, 10 ²⁰ –10 ²⁴ g, and 10–10 ³ M ⊙ . The last possibility is contentious but of special interest in view of the recent detection of black hole mergers by LIGO/Virgo. PBHs might have important consequences and resolve various cosmological conundra even if they account for only a small fraction of the dark matter density. In particular, those larger than 10 ³ M ⊙ could generate cosmological structures through the seed or Poisson effect, thereby alleviating some problems associated with the standard cold dark matter scenario, and sufficiently large PBHs might provide seeds for the supermassive black holes in galactic nuclei. More exotically, the Planck-mass relics of PBH evaporations or stupendously large black holes bigger than 10 ¹² M ⊙ could provide an interesting dark component. Expected final online publication date for the Annual Review of Nuclear and Particle Science, Volume 70 is October 19, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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A significant fraction of cosmological dark matter can be formed by very dense macroscopic objects, for example primordial black holes. Gravitational waves offer a promising way to probe these kinds of dark-matter candidates, in a parameter space region that is relatively untested by electromagnetic observations. In this work we consider an ensemble of macroscopic dark matter with masses in the range 101310^{-13}1 M1\ M_{\odot } orbiting a super-massive black hole. While the strain produced by an individual dark-matter particle will be very small, gravitational waves emitted by a large number of such objects will add incoherently and produce a stochastic gravitational-wave background. We show that LISA can be a formidable machine for detecting the stochastic background of such objects orbiting the black hole in the centre of the Milky Way, Sgr A ⁣\mathrm{A}^{\!*}, if a dark-matter spike of the type originally predicted by Gondolo and Silk forms near the central black hole.
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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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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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Observations have been carried out with SCUBA at the JCMT of 52 molecular cloud cores that do not contain any sign of protostellar activity. These are all therefore candidate prestellar cores, which are believed to represent the stage of star formation that precedes the formation of a protostar. 29 of the 52 cores were detected at 850 microns at varying levels of signal-to-noise ratio greater than 3 sigma at peak. The detected cores were split into 'bright' cores and `intermediate' cores, depending on their peak flux density at 850 microns. Cores with peak 850 microns flux densities greater than 170 mJy/beam were designated 'bright' (13 cores), while those flux densities below this value were designated 'intermediate' (16 cores). This dividing line corresponds to A_v~50 under typical assumptions. The data are combined with our previously published ISO data, and the physical parameters of the cores, such as density and temperature, are calculated. Detailed fitting of the bright core radial profiles shows that they are not critical Bonnor-Ebert spheres, in agreement with previous findings. However, we find that intermediate cores, such as B68 (which has previously been claimed to be a Bonnor-Ebert sphere), may in fact be consistent with the Bonnor-Ebert criterion, suggesting perhaps that cores pass through such a phase during their evolution. We make rough estimates of core lifetimes based on the statistics of detections and find that the lifetime of a prestellar core is roughly ~3x10^5 years, while that of a bright core is \~1.5x10^5 years. Comparisons with some magnetic and turbulence regulated collapse models show that no model can match all of the data. Models that are tuned to fit the total prestellar core lifetime, do not predict the relative numbers of cores seen at each stage. Comment: 23 pages, 52 figures, accepted by MNRAS, alternate PDF w/all figures available from http://www.astro.cf.ac.uk/pub/Derek.Ward-Thompson/publications.html
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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 have retrieved Spitzer archive data of pre-stellar cores taken with the Multiband Imaging Photometer for Spitzer (MIPS) at a wavelength of 160 μm. Seventeen images, containing 18 cores, were constructed. Flux densities were measured for each core, and background estimates were made. Mean off-source backgrounds were found to be 48 ± 10 MJy sr−1 in Taurus and 140 ± 55 MJy sr−1 in Ophiuchus. Consistency was found between the MIPS 170-μm and ISOPHOT 160-μm calibrations. Fourteen cores were detected both by MIPS and by our previous submillimetre surveys. Spectral energy distributions were made for each core, using additional 24- and 70-μm data from the Spitzer data archive, as well as previous infrared and submillimetre data. Previous temperature estimates were refined, and new temperature estimates were made where no Infrared Space Observatory (ISO) data exist. A temperature range of 8–18 K was found for the cores, with most lying in the range 10–13 K. We discount recent claims that a large number of pre-stellar cores may have been misclassified and in fact contain low-luminosity protostars detectable only by Spitzer. We find no new protostars in our sample other than that previously reported in L1521F. It is shown that this has a negligible effect on pre-stellar lifetime estimates.
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The conjecture that the ancient globular clusters (GCs) formed at the center of their own dark matter (DM) halos was first proposed by Peebles in 1984 and has recently been revived to explain the puzzling abundance patterns observed within many GCs. In this paper, we demonstrate that the outer stellar density profile of isolated GCs is very sensitive to the presence of an extended dark halo. The GCs NGC2419, located at 90kpc from the center of our Galaxy, and MGC1, located at ∼ 200kpc from the center of M31, are ideal laboratories for testing the scenario that GCs formed at the centers of massive dark halos. Comparing analytic models to observations of these GCs, we conclude that these GCs cannot be embedded within dark halos with a virial mass greater than 10 6 M ⊙, or, equivalently, the DM halo-mass-to-stellar mass ratio must be M DM/M * < 1. If these GCs have indeed orbited within weak tidal fields throughout their lifetimes, then these limits imply that these GCs did not form within their own dark halos. Recent observations of an extended stellar halo in the GC NGC1851 are also interpreted in the context of our analytic models. Implications of these results for the formation of GCs are briefly discussed. © 2011. The American Astronomical Society. All rights reserved.
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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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It is suggested that there may be a large number of gravitationally collapsed objects of mass 10–5 g upwards which were formed as a result of fluctuations in the early Universe. They could carry an electric charge of up to ± 30 electron units. Such objects would produce distinctive tracks in bubble chambers and could form atoms with orbiting electrons or protons. A mass of 10¹⁷ g of such objects could have accumulated at the centre of a star like the Sun. If such a star later became a neutron star there would be a steady accretion of matter by a central collapsed object which could eventually swallow up the whole star in about ten million years.
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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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Using the Vlasov equation, we show that massive galactic halos cannot be composed of stable neutral leptons of mass < or approx. = 1 MeV. Since most of the mass in clusters of galaxies probably consists of stripped halos, we conclude that the ''missing mass'' in clusters does not consist of leptons of mass < or approx. = 1 MeV (e.g., muon or electron neutrinos). Lee and Weinberg's hypothetical heave leptons (mass approx. = 1 GeV) are not ruled out by this argument.
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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 capture of cold dark matter species, and especially primordial black holes, during the formation of gravitationally bound objects is analyzed. It is shown that the best conditions for an efficient gravitational capture were at the epoch preceding the galaxy formation, when the first astrophysical objects with masses of the order of Jeans mass 10(5-10^6 Msun) were forming. Black hole haloes around old globular clusters, dark matter clusters and Population III stars are considered, and in each case the total mass of the halo and its luminosity due to the Hawking emission are found. Among all the objects considered, large (M >~ 10(5 Msun) ), nearby (within ~ 5 kpc from the Sun) globular clusters are shown to provide the best prospects for detection of the black holes. First, black hole haloes around the globular clusters have the highest brightness near 100 MeV, which is within the reach of EGRET capabilities, and provide distinct observational features. Second, globular clusters are extensively studied at other wavelengths and represent a well-defined target for gamma -ray detectors. We have also considered the probability of detecting an isolated black hole bound to the Sun. Our estimates of the mass of gravitationally captured haloes are applicable to any cold dark matter particles.
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Radiative hydrodynamical models of protostellar collapse are used to calculate the spectral energy distributions of single and binary protostars at the phase of formation of the first (outer) protostellar core. In accordance with the established nomenclature, where classes 0, I, II, and III form a sequence in time, we term these pre-class 0 objects to be class-I ('class minus one') objects. These class -I objects are characterized by central core temperatures of approximately 200 K, envelope temperatures of approximately 10 K, and substantial far-infrared and submillimeter-wave fluxes. While undetectable by IRAS, these objects should be detectable by Infrared Space Observatory (ISO) and Space Infrared Telescope Facility (SITF) at 60 micrometer and longer wavelengths. First protostellar cores exist for times on the order of a few percent of the total collapse time, implying that a small fraction of all protostellar objects should be class -I objects.
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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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Numerical calculations of the dynamics of a spherically symmetric collapsing proto-star of one solar mass have been made for various initial conditions. Calculations have also been made for masses of 2M⊙ and 5M⊙. In all cases the collapse is found to be extremely non-homologous and is such that a very small part of the cloud's mass at the centre reaches stellar densities and stops collapsing before most of the cloud has had time to collapse very far. The stellar core thus formed subsequently grows in mass as material falls into it, finally becoming an ordinary star when all of the proto-stellar material has been accreted. During most of this time the stellar core is completely obscured by the dust in the infalling cloud, the absorbed radiation reappearing in the infra-red as thermal emission from the dust grains. The resulting star is almost a conventional Hayashi pre-main sequence model, but it appears rather low on the Hayashi track. For masses much greater than about 2M⊙ the convective Hayashi phase does not exist at all. It appears that certain properties of T Tauri stars may find explanation in the results of the present calculations. In an appendix to the paper it is shown that limiting forms may be derived for the density and velocity distributions near the centre of an isothermally collapsing sphere. This may be shown to be possible also for a sphere with a polytropic equation of state. Numerical results are presented for the limiting solution in the isothermal case.
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If gamma-ray bursters are at cosmological distances, they can be used to probe for 'femtolenses', extremely small (about 10 exp -13 - 10 exp -16 solar mass) dark-matter objects. The time delay induced by such a lens would be about 10 exp -17 - 10 exp -20 s, approximately equal to the period of a gamma ray. Interference between the two images would induce a characteristic interference pattern as a function of detected frequency. The pattern would be stable on time scales of 1 s, but might slowly drift on time scales of 10 s in response to the relative motion of the lens and source. The signal from a femtolens would be quite distinct and would be well within the sensitivity of present detectors.
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A database of parameters for globular star clusters in the Milky Way is described which is available in electronic form through the WorldWideWeb. The information in the catalog includes up-to-date measurements for cluster distance, reddening, luminosity, colors and spectral types, velocity, structural and dynamical parameters, horizontal branch morphology, metallicity, and other quantities. This catalog will be updated regularly and maintained in electronic form for widest possible accessibility.
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The role of ambipolar diffusion in the formation of molecular cloud cores and protostars is examined critically. The origin and physical meaning of a criterion for quasistatic or dynamic core contraction in otherwise magnetically supported clouds is explained briefly on the basis of analytical considerations. The relative magnitude of three natural length scales, which are unavoidably present in (realistic, three-dimensional) molecular clouds, determines the typical mass that can go into a protostar (˜1 Msun). We formulate the problem of the self-initiated contraction (due to ambipolar diffusion) of cylindrically symmetric, self-gravitating, isothermal, magnetic clouds embedded in a medium of constant thermal and magnetic pressures. If it were not for ambipolar diffusion, these model clouds would exist in exact equilibrium states indefinitely. The equations themselves contain three dimensionless free parameters: the ratio αc of magnetic and thermal pressures in the core of the initial equilibrium state; the ratio νff of the initial free-fall and neutral-ion collision times (divided by π1/2) in the core; and the exponent k in the parametrization ni ∞ nkn of the ion density in terms of the neutral density. The boundary conditions introduce, in general, two additional free parameters, namely, the ratio of the initial surface and central neutral densities, and the ratio of the initial surface and central magnetic field strengths. The initial conditions introduce no new free parameters in the problem. In fact, they remove one free parameter if α is taken to be constant in the initial equilibrium state. The numerical method developed to follow the evolution of these model clouds, which involves an adaptive grid, is characterized by a fractional error ≃10-5 in the approximation of the forces everywhere in a model cloud except at the surface, where the error increases to 10-2 without degrading the accuracy anywhere else in the interior; a maximum relative error of the implicit time-integrator one to two orders of magnitude smaller than that introduced by spatial discretization; and a numerical diffusion of magnetic flux, introduced by the advection scheme, typically a few × 10-5. The results, including an extensive parameter study, as they relate to the formation of cores and protostars are described in a following paper.
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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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We present new Keck/HIRES observations of six red giants in the globular cluster NGC 2419. Although the cluster is among the most distant and most luminous in the Milky Way, it was considered chemically ordinary until very recently. Our previous work showed that the near-infrared Ca II triplet line strength varied more than expected for a chemically homogeneous cluster, and that at least one star had unusual abundances of Mg and K. Here, we confirm that NGC 2419 harbors a population of stars, comprising about one third of its mass, that is depleted in Mg by a factor of 8 and enhanced in K by a factor of 6 with respect to the Mg-normal population. Although the majority, Mg-normal population appears to have a chemical abundance pattern indistinguishable from ordinary, inner halo globular clusters, the Mg-poor population exhibits dispersions of several elements. The abundances of K and Sc are strongly anti-correlated with Mg, and some other elements (Si and Ca among others) are weakly anti-correlated with Mg. These abundance patterns suggest that the different populations of NGC 2419 sample the ejecta of diverse supernovae in addition to AGB ejecta. However, the abundances of Fe-peak elements except Sc show no star-to-star variation. We find no nucleosynthetic source that satisfactorily explains all of the abundance variations in this cluster. Because NGC 2419 appears like no other globular cluster, we reiterate our previous suggestion that it is not a globular cluster at all, but rather the core of an accreted dwarf galaxy.
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Varied evidence suggests that galaxies consist of roughly 10 percent baryonic matter by mass and that baryons sink dissipatively by about a factor of 10 in. radius during galaxy formation. It is shown that such infall strongly perturbs the underlying dark matter distribution, pulling it inward and creating cores that are considerably smaller and denser than would have evolved without dissipation. Any discontinuity between the baryonic and dark matter mass distributions is smoothed out by the coupled motions of the two components. If dark halos have large core radii in the absence of dissipation, the above infall scenario yields rotation curves that are flat over large distances, in agreement with observations of spiral galaxies. Such large dissipationless cores may plausibly result from large internal kinetic energy in protogalaxies at maximum expansion, perhaps as a result of subclustering, tidal effects, or anisotropic collapse.
Article
Precise radial velocity measurements from high-resolution echelle spectrometer on the Keck I telescope are presented for 40 stars in the outer halo globular cluster NGC 2419. These data are used to probe the cluster's stellar mass function and search for the presence of dark matter in this cluster. NGC 2419 is one of the best Galactic globular clusters for such a study due to its long relaxation time (Tr 0≈ 1010 yr) and large Galactocentric distance (RGC≈ 90 kpc)– properties that make significant evolutionary changes in the low-mass end of the cluster mass function unlikely. We find a mean cluster velocity of 〈vr〉=−20.3 ± 0.7 km s−1 and an internal velocity dispersion of σ= 4.14 ± 0.48 km s−1, leading to a total mass of (9.0 ± 2.2) × 105 M⊙ and a global mass-to-light ratio of M/LV= 2.05 ± 0.50 in solar units. This mass-to-light ratio is in good agreement with what one would expect for a pure stellar system following a standard mass function at the metallicity of NGC 2419. In addition, the mass-to-light ratio does not appear to rise towards the outer parts of the cluster. Our measurements therefore rule out the presence of a dark matter halo with mass larger than ∼107 M⊙ inside the central 500 pc, which is lower than what is found for the central dark matter densities of dSph galaxies. We also discuss the relevance of our measurements for alternative gravitational theories such as Modified Newtonian Dynamics, and for possible formation scenarios of ultracompact dwarf galaxies.
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 isolate a sample of 43 upper RGB stars in the extreme outer halo Galactic globular cluster NGC 2419 from two Keck/DEIMOS slitmasks. The probability that there is more than one contaminating halo field star in this sample is extremely low. Analysis of moderate resolution spectra of these cluster members, as well as of our Keck/HIRES high resolution spectra of a subsample of them, demonstrates that there is a small but real spread in Ca abundance of ~ 0.2 dex within this massive metal-poor globular cluster. This provides additional support to earlier suggestions that NGC 2419 is the remnant of a dwarf galaxy accreted long ago by the Milky Way.
Article
The conjecture that the ancient globular clusters (GCs) formed at the center of their own dark matter halos was first proposed by Peebles (1984), and has recently been revived to explain the puzzling abundance patterns observed within many GCs. In this paper we demonstrate that the outer stellar density profile of isolated GCs is very sensitive to the presence of an extended dark halo. The GCs NGC 2419, located at 90 kpc from the center of our Galaxy, and MGC1, located at ~200 kpc from the center of M31, are ideal laboratories for testing the scenario that GCs formed at the centers of massive dark halos. Comparing analytic models to observations of these GCs, we conclude that these GCs cannot be embedded within dark halos with a virial mass greater than 10^6 Msun, or, equivalently, the dark matter halo mass-to-stellar mass ratio must be Mdm/M_*<1. If these GCs have indeed orbited within weak tidal fields throughout their lifetimes, then these limits imply that these GCs did not form within their own dark halos. Recent observations of an extended stellar halo in the GC NGC 1851 are also interpreted in the context of our analytic models. Implications of these results for the formation of GCs are briefly discussed.
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
Article
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
If the cosmological dark matter has a component made of small primordial black holes (BHs), they may have a significant impact on the physics of the first stars and on the subsequent formation of massive BHs. Primordial BHs would be adiabatically contracted into these stars and then would sink to the stellar centre by dynamical friction, creating a larger BH which may quickly swallow the whole star. If these primordial BHs are heavier than ∼1022 g, the first stars would likely live only for a very short time and would not contribute much to the reionization of the Universe. They would instead become 10–103 M⊙ BHs which (depending on subsequent accretion) could serve as seeds for the super-massive BHs seen at high redshifts as well as those inside galaxies today.
Article
A model of baryogenesis is described which gives rise to fluctuations in baryon number that are large on small scales but of low amplitude on large scales. This provides a mechanism for primordial black-hole formation, and allows the possibility of a critical density of dark matter in baryonic (and antibaryonic) form. Since high-density regions naturally possess both signs of baryonic excess, our model also predicts a small fraction of the mass density of the Universe to be in the form of compact antibaryonic regions. These objects may be observable via a redshifted annihilation feature in the diffuse extragalactic gamma-ray background, as both steady sources of gamma-ray radiation and annihilation-powered gamma-ray bursters at cosmological distances, by a distortion of the spectrum of the 3K background radiation, or by the presence of antihelium nuclei as a rare component of high-energy cosmic rays.
Article
A mechanism is identified whereby dark matter (DM) in protostellar halos dramatically alters the current theoretical framework for the formation of the first stars. Heat from neutralino DM annihilation is shown to overwhelm any cooling mechanism, consequently impeding the star formation process and possibly leading to a new stellar phase. A "dark star" may result: a giant ( greater, similar 1 AU) hydrogen-helium star powered by DM annihilation instead of nuclear fusion. Observational consequences are discussed.