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Dark Matter and the First Stars: A New Phase of Stellar Evolution
Abstract
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.
... Gravitational collapse in this scenario could lead to the formation of dark stars, which, according to Refs. [16][17][18], counteract further collapse through radiation pressure. However, such stars likely no longer exist because DM annihilations would have significantly reduced the DM population, causing these dark stars to vanish over time. ...
... 15)). The green line represents the best linear fit to our bosonic dark matter models, namely Eq. (16). The orange line is the best linear fit to the fermionic dark matter stars and corresponds to Eq. (17). ...
... One should note that these curves represent an ideal case, while the lines would be thicker if uncertainties were taken into account. The intersection point of the two curves corresponds to the estimates of the mass M and moment of inertia I of a bosonic source that can be achieved by using the universal relations (24) and (26), with values for the coefficients a 1 , a 2 , a 3 , b 1 , b 2 given by those of Eq. (10) and (16). In order to compare the estimates with the true values of the bosonic dark matter model of which we assume to have measured the f -mode frequency and damping time, we plot the model's mass versus effective compactness η = M 3 /I as a black point. ...
Theoretical models of self-interacting dark matter offer a promising solution to several unresolved issues within the collisionless cold dark matter framework. For asymmetric dark matter, these self-interactions may encourage gravitational collapse, potentially leading to the creation of compact objects primarily composed of dark matter. By considering both fermionic and bosonic equations of state, we analyze the equilibrium structure of non-rotating dark stars, examining their bulk properties and comparing them with baryonic neutron stars. We show that the frequency and damping rate of f-mode oscillations of dark compact stars can be expressed in terms of universal functions of stellar mass, radius and moment of inertia. Finally, by employing the universality in the f-mode, we propose a scheme to infer accurate values of the physical parameters of dark compact stars from their f-mode gravitational wave signal.
... An intriguing distinct class of first stars, known as dark stars (DSs), powered by heating from DM constituting a small fraction of their mass instead of fusion, has been put forth and that could seed SMBHs [16][17][18]. DM heating can be a general byproduct of annihilation of weakly interacting massive particles (WIMPs) [16], but can also arise in contexts such as self-interacting DM [19]. During formation, the contraction of baryonic matter induces adiabatic contraction of DM, leading to high DM densities sufficient for efficient annihilation. ...
... An intriguing distinct class of first stars, known as dark stars (DSs), powered by heating from DM constituting a small fraction of their mass instead of fusion, has been put forth and that could seed SMBHs [16][17][18]. DM heating can be a general byproduct of annihilation of weakly interacting massive particles (WIMPs) [16], but can also arise in contexts such as self-interacting DM [19]. During formation, the contraction of baryonic matter induces adiabatic contraction of DM, leading to high DM densities sufficient for efficient annihilation. ...
... As M (r) increases due to baryonic inflow, r must decrease, leading to the adiabatic contraction of DM. This process concentrates DM at the center of the halo, where it can reach sufficiently high densities for efficient annihilation [16]. The energy released by DM annihilation heats the surrounding baryonic gas, stalling further collapse. ...
First stars powered by dark matter (DM) heating instead of fusion can appear in the early Universe from theories of new physics. These dark stars (DSs) can be significantly larger and cooler than early Population III stars, and could seed supermassive black holes (SMBHs). We show that neutrino emission from supermassive DSs provides a novel window into probing SMBH progenitors. We estimate first DS constraints using data from Super-Kamiokande and IceCube neutrino experiments, and consistent with James Webb Space Telescope observations. Upcoming neutrino telescopes offer distinct opportunities to further explore DS properties.
... 6 On the other hand, the large dark matter (DM) abundance at the centers of the minihalos may alter these conclusions. DM, whether it be weakly interacting massive particles (WIMPs), self-interacting dark matter (SIDM), or other candidates, may provide a heat source that halts the collapse of the hydrogen clouds (Spolyar et al. 2008) and leads to a dark star (DS), a star made almost entirely of hydrogen and helium but powered by DM heating (for a review, see Freese et al. 2016). These dark stars may grow to becomes very massive and bright supermassive dark stars (SMDSs; Freese et al. 2010), up to 10 6 M e and 10 10 L e , and be visible in current and upcoming telescopes, including the James Webb Space Telescope (JWST; Ilie et al. 2012) and, as is the subject of the current paper, the upcoming Roman Space Telescope (RST). ...
... The standard picture of the formation of the first stars may be drastically changed due to the role of the large DM abundance at the center of the host minihalo, leading to a heat source for the collapsing molecular cloud. Spolyar et al. (2008) first considered the possibility that, if DM consists of WIMPs, their annihilation products would be trapped inside the collapsing molecular cloud, thermalize with the cloud, and heat it up. This DM heating can overcome the dominant hydrogen cooling mechanisms and thereby halt the collapse of the protostellar gas cloud. ...
... The literature on the possibility that DM annihilation might have effects on stars dates back to the '80s and early '90s, with the initial work studying the effects on current day stars (e.g., Krauss et al. 1985;Gould 1988Gould , 1992Salati & Silk 1989;Gould & Raffelt 1990, to name a few). Regarding the DM heating effects on the first stars, we mention Spolyar et al. (2008Spolyar et al. ( , 2009, Freese et al. (2008aFreese et al. ( , 2008bFreese et al. ( , 2010, Taoso et al. (2008), Yoon et al. (2008), Iocco et al. (2008), Casanellas & Lopes (2009), Ripamonti et al. (2009Ripamonti et al. ( , 2010, Gondolo et al. (2010), Hirano et al. (2011), Sivertsson & Gondolo (2011), Ilie et al. (2012, and Gondolo et al. (2022). For reviews, see Ch. 29 ("Dark Matter and Stars") of Bertone (2010), Tinyakov et al. (2021), andFreese et al. (2016). ...
Supermassive dark stars (SMDS) are luminous stellar objects formed in the early Universe at redshift z ∼ 10–20, made primarily of hydrogen and helium, yet powered by dark matter. We examine the capabilities of the Roman Space Telescope (RST), and find it able to identify ∼10 ⁶ M ⊙ SMDSs at redshifts up to z ≃ 14. With a gravitational lensing factor of μ ∼ 100, RST could identify SMDS as small as ∼10 ⁴ M ⊙ at z ∼ 12 with ∼10 ⁶ s exposure. Differentiating SMDSs from early galaxies containing zero metallicity stars at similar redshifts requires spectral, photometric, and morphological comparisons. With only RST, the differentiation of SMDS, particularly those formed via adiabatic contraction with M ≳ 10 ⁵ M ⊙ and lensed by μ ≳ 100, is possible due to their distinct photometric signatures from the first galaxies. Those formed via dark matter capture can be differentiated only by image morphology: i.e., point object (SMDSs) versus extended object (sufficiently magnified galaxies). By additionally employing James Webb Space Telescope (JWST) spectroscopy, we can identify the He ii λ 1640 absorption line, a smoking gun for SMDS detection. Although RST does not cover the required wavelength band (for z emi ≳ 10), JWST does; hence, the two can be used in tandem to identify SMDS. The detection of SMDS would confirm a new type of star powered by dark matter and may shed light on the origins of the supermassive black holes powering bright quasars observed at z ≳ 6.
... • In 2005, E. Ripamonti and T. Abel discussed the role of cold DM in the formation of Primordial Luminous Objects [8]. A mechanism whereby DM in protostellar halos plays a role in the formation of the first stars is discussed by D. Spolyar, K. Freese, and P. Gondolo [9]. Heat from neutralino DM annihilation is shown to overwhelm any cooling mechanism, consequently impeding the star formation process. ...
... Heat from neutralino DM annihilation is shown to overwhelm any cooling mechanism, consequently impeding the star formation process. A dark star powered by DM annihilation instead of nuclear fusion may result [9]. Dark stars are in hydrostatic and thermal equilibrium, but with an unusual power source [10]. ...
... • The most secure oldest galaxy is GLASS-z13 (z ≈ 13, light-travel distance of 13.4572 Byr) that has already built up 9 10 M in stars; ...
... They are thought to grow to 100 − 1000M ⊙ . 1 On the other hand, the large dark matter abundance at the centers of the minihalos may alter these conclusions. Dark matter, whether it be Weakly Interacting Massive Particles, Self-Interacting Dark Matter, or other candidates, may provide a heat source that halts the collapse of the hydrogen clouds (Spolyar et al. (2008)) and leads to a Dark Star, a star made almost entirely of hydrogen and helium but powered by dark matter heating (for a review, see Freese et al. (2016)). These Dark Stars may grow to becomes very massive and bright Supermassive Dark Stars (SMDS) (Freese et al. (2010)), up to 10 6 M ⊙ and 10 10 L ⊙ , and be visible in current and upcoming telescopes, including the James Webb Space Telescope (JWST) (Ilie et al. 2012) and, as is the subject of the current paper, the upcoming Roman Space Telescope (RST). ...
... The standard picture of the formation of the first stars may be drastically changed due to the role of the large dark matter abundance at the center of the host minihalo, leading to a heat source for the collapsing molecular cloud. Spolyar et al. (2008) first considered the possibility that, if dark matter consists of Weakly Interacting Massive Particles (WIMPs), their annihilation products would be trapped inside the collapsing molecular cloud, thermalize with the cloud, and heat it up. This dark matter heating can overcome the dominant hydrogen cooling mechanisms and thereby halt the collapse of the protostellar gas cloud. ...
... Krauss et al. 1985;Gould 1988;Salati & Silk 1989;Gould & Raffelt 1990;Gould 1992, to name a few). Regarding the DM heating effects on the first stars we mention Spolyar et al. (2008Spolyar et al. ( , 2009); Freese et al. (2008b,a); Freese et al. (2010); Taoso et al. (2008); Yoon et al. (2008); Iocco et al. (2008); Casanellas & Lopes (2009); Ripamonti et al. (2009Ripamonti et al. ( , 2010; Gondolo et al. (2010); Hirano et al. (2011); Sivertsson & Gondolo (2011); Ilie et al. (2012). For reviews see Ch. 29 ("Dark Matter and Stars") of Bertone (2010), Tinyakov et al. (2021) and Freese et al. (2016). ...
The first bright objects to form in the Universe at redshift might have been Dark Stars, made primarily of hydrogen and helium but powered by dark matter. In this study, we investigate the detectability of Supermassive Dark Stars (SMDS) by the Roman Space Telescope. RST will be able to detect SMDSs at redshifts as high as . In cases with gravitational lensing factors of , RST will be able to find SMDS as small as at with s of exposure. To differentiate SMDS from early galaxies containing zero metallicity stars at similar redshifts, we compare their spectra, photometry in RST bands, color indexes and image morphology. With RST alone, the differentiation is possible only for limited cases: SMDS formed via "adiabatic contraction" (DM pulled into the star via gravity alone) with and lensed by have distinct photometric signatures from those of the first galaxies. For SMDSs formed via "dark matter capture," their spectra are degenerate to those of many galaxies with little to no nebular emission. Thus with RST alone, the only way to tell them apart from first galaxies would be via image morphology: i.e. point object (SMDSs) vs. extended object (sufficiently magnified galaxies). However, if the same objects are further examined by JWST spectroscopy, a "smoking gun" for detection of SMDS is the HeII 1640 absorption line. While RST does not cover the wavelength band required to find this line (for ), JWST does. Hence the two detectors can be used together in identifying SMDS. The confirmed detection of any SMDSs will provide evidence for a new type of star, powered by dark matter. Moreover, such massive stars can also be natural progenitors of the supermassive black holes powering the extremely bright quasars observed at .
... where Mtot = M DM +M , and we are neglecting the effect of the gas evolution on the dark matter (though see Spolyar et al. 2008). In our molecular cooling mini-halo, we take a dark matter density profile informed by the simulations of Hirano et al. (2014), which generated a sample of ∼ 100 clouds collapsing in haloes of masses between 10 5 M⊙ and 10 6 M⊙ and at redshifts between 10 ≲ z ≲ 35. ...
... In addition to the fiducial profile Eq. (2.9), we consider both an NFW profile appropriate to a halo of mass 5 × 10 5 M⊙ with a concentration parameter c = 2.8 (i.e. a significantly larger dark matter density than the fiducial case) and the case of no dark matter whatsoever. Adiabatic contraction (Blumenthal et al. 1986) of the dark matter in response to the gas collapse can greatly enhance the dark matter density compared to any of these estimates, which may in turn have dramatic effects on the star formation process (Spolyar et al. 2008), a possibility we do not treat here. The gas density profiles in our three assumed dark matter profiles are shown in Fig. B1. ...
We present an analytic description of the spherically symmetric gravitational collapse of radiatively cooling gas clouds. The approach is based on developing the "one-zone" density-temperature relationship of the gas into a full dynamical model. We convert this density-temperature relationship into a barotropic equation of state, which we use to calculate the density and velocity profiles of the gas. From these quantities we calculate the time-dependent mass accretion rate onto the center of the cloud. The approach clarifies the mechanism by which radiative cooling induces gravitational instability. In particular, we distinguish the rapid, quasi-equilibrium contraction of a cooling gas core to high central densities from the legitimate instability this contraction establishes in the envelope. We develop a refined criterion for the mass scale of this instability, based only on the chemical-thermal evolution in the core. We explicate our model in the context of a primordial mini-halo cooled by molecular hydrogen, and then provide two further examples, a delayed collapse with hydrogen deuteride cooling and the collapse of an atomic cooling halo. In all three cases, our results agree well with full hydrodynamical treatments.
... This criterion is parameterized by an isolation distance iso , expressed in physical units, of the order of ≲100 kpc. The physical mechanism that allows growth of Pop III.1 protostars to high mass, i.e., ≳ 10 4 ⊙ , is the influence of dark matter annihilation (DMA) on the protostellar structure (Spolyar et al. 2008;Natarajan et al. 2009;Freese et al. 2010;Rindler-Daller et al. 2015). The fiducial assumption is that dark matter is composed of a weakly interacting massive particles (WIMPs), which undergoes self-annihilation with a weak interaction cross-section. ...
... The physical mechanism that may allow SMBH formation is the impact of dark matter annihilation heating on the structure of the Pop III.1 protostar (Spolyar et al. 2008;Natarajan et al. 2009;Rindler-Daller et al. 2015). The expected effect is to keep the protostar relatively large and cool, thus emitting a weak flux of ionising radiation. ...
We present an implementation of Pop III.1 seeding of supermassive black holes (SMBHs) in a theoretical model of galaxy formation and evolution to assess the growth the SMBH population and the properties of the host galaxies. The model of Pop III.1 seeding involves SMBH formation at redshifts in dark matter minihalos that are isolated from external radiative feedback, parameterized by isolation distance . Within a standard CDM cosmology, we generate dark matter halos using the code \textsc{pinocchio} and seed them according to the Pop III.1 scenario, exploring values of from 50 to 100~kpc (proper distance). We consider two alternative cases of SMBH seeding: a Halo Mass Threshold (HMT) model in which all halos are seeded with black holes; an All Light Seed (ALS) model in which all halos are seeded with low, stellar-mass black holes. We follow the redshift evolution of the halos, populating them with galaxies using the GAlaxy Evolution and Assembly theoretical model of galaxy formation, including accretion on SMBHs and related feedback processes. Here we present predictions for the properties of galaxy populations, focusing on stellar masses, star formation rates, and black hole masses. The local, metrics of occupation fraction as a function of the galaxy stellar mass, galaxy stellar mass function (GSMF), and black hole mass function (BHMF) all suggest a constraint of kpc. We discuss the implications of this result for the Pop III.1 seeding mechanism.
... Beyond its gravitational influence, dark matter, through its annihilation channels, might have significantly impacted the formation of Pop III stars. Such annihilation events could act as an additional heat sources, thereby potentially inhibiting protostar formation by offsetting essential cooling mechanisms [95,96]. In scenarios where a high dark matter density exists at the gas cloud's location, if some annihilation products are trapped and thermalized within the cloud, and with this dark matter-induced heating surpassing expected cooling effects, a novel stellar phase, known as the "dark star" phase, could emerge. ...
... In scenarios where a high dark matter density exists at the gas cloud's location, if some annihilation products are trapped and thermalized within the cloud, and with this dark matter-induced heating surpassing expected cooling effects, a novel stellar phase, known as the "dark star" phase, could emerge. This phase could manifest itself as a giant hydrogen-helium star (R ≳ 1 AU), which would be powered by dark matter annihilation instead of nuclear fusion [95]. Furthermore, with the ongoing capture of dark matter, these objects may evolve into supermassive dark stars, with masses larger than (10 5 -10 7 )M ⊙ and luminosities exceeding (10 9 -10 11 )L ⊙ [97]. ...
Tensions in the measurements of neutron and kaon weak decays, such as of the neutron lifetime, may speak to the existence of new particles and dynamics not present in the Standard Model (SM). In scenarios with dark sectors, particles that couple feebly to those of the SM appear. We offer a focused overview of such possibilities and describe how the observations of neutron stars, which probe either their structure or dynamics, limit them. In realizing these constraints, we highlight how the assessment of particle processes within dense baryonic matter impacts the emerging picture—and we emphasize both the flavor structure of the constraints and their broader connections to cogenesis models of dark matter and baryogenesis.
... Abel, Bryan & Norman 2002 ;Bromm, Coppi & Larson 2002 ;Tan & McK ee 2004 ;McK ee & Tan 2008 ;Hosoka wa et al. 2011 ;Susa, Hase ga wa & Tominaga 2014 ), which would only have the ability to produce stellar-mass black holes, i.e. relati vely lo w-mass seeds. Ho we ver, as discussed in more detail below, Pop III SMBH seeding models have been re vi ved by Banik, Tan & Monaco ( 2019 ) when allowing for the potential effects of dark matter self-annihilation on the mass scale of formed stars (Spolyar, Freese & Gondolo 2008 ;Natarajan, Tan & OShea 2009 ;Freese et al. 2010 ;Rindler-Daller et al. 2015 ). ...
... metal free) stars forming in the first dark matter minihaloes to form in a given region of the universe and so are isolated from other stellar or SMBH feedback sources (McKee & Tan 2008 ). In this model, it is assumed that in the absence of any significant radiative (or mechanical) feedback, a single dominant protostar forms at the centre of the minihalo and has its structure affected by the energy input from Weakly Interacting Massiv e P article (WIMP) dark matter self annihilation inside the protostar (Spolyar et al. 2008 ;Natarajan et al. 2009 ;Freese et al. 2010 ;Rindler-Daller et al. 2015 ). Such protostars maintain relatively cool photospheres and thus low levels of ionizing feedback, which allows efficient accretion of the baryonic content of the minihalo, i.e. ∼ 10 5 M , to form a supermassive star, which subsequently collapses efficiently to an SMBH after a few Myr. ...
We present predictions for cosmic evolution of populations of supermassive black holes (SMBHs) forming from Population III.1 seeds, i.e., early, metal-free dark matter minihalos forming far from other sources, parameterized by isolation distance, diso. Extending previous work that explored this scenario to z = 10, we follow evolution of a (60 Mpc)3 volume to z = 0. We focus on evolution of SMBH comoving number densities, halo occupation fractions, angular clustering and 3D clustering, exploring a range of diso constrained by observed local number densities of SMBHs. We also compute synthetic projected observational fields, in particular a case comparable to the Hubble Ultra Deep Field. We compare Pop III.1 seeding to a simple halo mass threshold model, commonly adopted in cosmological simulations of galaxy formation. Major predictions of the Pop III.1 model include that all SMBHs form by z ∼ 25, after which their comoving number densities are near-constant, with low merger rates. Occupation fractions evolve to concentrate SMBHs in the most massive halos by z = 0, but with rare cases of SMBHs in halos down to ∼108 M⊙. The diso scale at epoch of formation, e.g., 100 kpc-proper at z ∼ 30, i.e. ∼3 Mpc-comoving, is imprinted in the SMBH two-point angular correlation function, remaining discernible as a low-amplitude feature to z ∼ 1. The SMBH 3D two-point correlation function at z = 0 also shows lower amplitude compared to equivalently massive halos. We discuss prospects for testing these predictions with observational surveys of SMBH populations.
... New astrophysical objects that have not yet been experimentally detected could be discovered, such as those composed of dark matter, known as dark stars [18,19]. An interesting work that analyzes the emission of gravitational waves in alternative theories of compact binary systems can be reviewed in [20]. ...
In this work, we examine head-on collisions, produced by other work, of -boson stars, potential candidates for dark matter compact objects. We begin with a review of the general properties and features of these stars, leveraging results from prior studies to analyze the gravitational wave signals generated by such collisions. Considering a maximum distance of 100 Mpc for potential events, we identify the range of scalar field masses and frequencies for these stars that would render the gravitational waves detectable by current gravitational wave observatories. The ranges obtained for the scalar field masses are eV. Additionally, we process the resulting signals to generate simulated observatory images, highlighting their similarities and differences compared to those produced by black hole collisions.
... An alternative theoretical model of SMBH seeding in cosmological volumes is based on the formation of supermassive Pop III.1 stars in locally isolated dark matter minihalos (Banik et al. 2019;Cammelli et al. 2025) (see Tan et al. 2024, for a review). It relies on the physical mechanism of dark matter annihilation heating to change the structure of the protostar (Spolyar et al. 2008;Tan 2008;Natarajan et al. 2009;Freese et al. 2009Freese et al. , 2010Rindler-Daller et al. 2015). In particular, if the protostar can be kept in a large, swollen state relative to that of the zero age main sequence (ZAMS) structure, then it may avoid the strong ionizing feedback that acts to limit the growth of "standard" Pop III stars (Tan & McKee 2004;McKee & Tan 2008;Tan et al. 2010;Hosokawa et al. 2011;Hirano et al. 2014;Susa et al. 2014). ...
Understanding the origin and evolution of supermassive black holes (SMBH) stands as one of the most important challenges in astrophysics and cosmology, with little current theoretical consensus. Improved observational constraints on the cosmological evolution of SMBH demographics are needed. Here we report results of a search via photometric variability for SMBHs appearing as active galactic nuclei (AGN) in the cosmological volume defined by the Hubble Ultra Deep Field (HUDF). This work includes particular focus on a new observation carried out in 2023 with the \textit{Hubble Space Telescope (HST)} using the WFC3/IR/F140W, which is compared directly to equivalent data taken 11 years earlier in 2012. Two earlier pairs of observations from 2009 to 2012 with WFC3/IR/F105W and WFC3/IR/F160W are also analysed. We identify 443, 149, and 78 AGN candidates as nuclear sources that exhibit photometric variability at a level of 2, 2.5 and 3~ in at least one filter. This sample includes 29, 14, and 9 AGN at redshifts , when the Universe was ~Myr old. After variability and luminosity function (down to mag) completeness corrections, we estimate the co-moving number density of SMBHs, . At , . At low-z our observations are sensitive to AGN fainter than mag, and we estimate . We discuss how these results place strong constraints on a variety of SMBH seeding theories.
... Finally, the environment of the Pop III star is perfect for this analysis: since these stars lived and died in the early universe, the ambient DM density was far higher, easily attaining ρ χ ∼ 10 16 GeV/cm 3 [e.g. 29,33]. So, the question becomes whether the improved DM capture ability of the Population III star is enough for it to compete with a local NS in terms of constraining power, and as it turns out, the answer is complicated. ...
In this work we explore the potential for Neutron Stars (NSs) at the Galactic center and Population~III stars to constrain Asymmetric Dark Matter (ADM). We demonstrate that for NSs in an environment of sufficiently high DM density (\rhox\gtrsim10^{9}\unit{GeV/cm^3}), the effects of both multiscatter capture and DM evaporation cannot be neglected. If a Bose Einstein Condensate (BEC) forms from ADM, then its low temperature and densely cored profile render evaporation from the BEC negligible, strengthening detectability of low-mass DM. Because of this, we find that the most easily observable Population III stars could be highly effective at constraining high- low-\mx DM, maintaining efficacy below \mx=10^{-15}\unit{GeV} thanks to their far lower value of \mx at which capture saturates to the geometric limit. Finally, we derive closed-form approximations for the evaporation rate of DM from arbitrary polytropic objects.
... Because the latter cross-section is closer to the cross-section presently probed by direct detection experiments [4,5], we will focus on neutron star probes of dark matter in the next section. While our focus here will be on dark matter which annihilates inside and thereby heats neutron stars, there are many other ways multiscatter stellar capture could be used to probe dark matter, including neutron star implosions [16,23,24,[26][27][28][29][30][31][32][33][34][35], monopole-induced nucleon decay [36,37], white dwarf heating [17,38,39], Type Ia supernova ignition [18,19], neutrino signatures of superheavy dark matter [40,41], and dark matter-powered stars [42][43][44][45]. ...
Dark matter may be discovered through its capture in stars and subsequent annihilation. It is usually assumed that dark matter is captured after a single scattering event in the star, however this assumption breaks down for heavy dark matter, which requires multiple collisions with the star to lose enough kinetic energy to become captured. We analytically compute how multiple scatters alter the capture rate of dark matter and identify the parameter space where the affect is largest. Using these results, we then show how multiscatter capture of dark matter on compact stars can be used to probe heavy ( TeV) dark matter with remarkably small dark matter-nucleon scattering cross-sections. As one example, it is demonstrated how measuring the temperature of old neutron stars in the Milky Way's center provides sensitivity to high mass dark matter with dark matter-nucleon scattering cross-sections smaller than the xenon direct detection neutrino floor.
... On the other hand, the formation of SMBH seeds from collapse of an axion star is quite different to the mechanism of "Dark Stars" in WIMP models with large annihilation rates [79][80][81][82][83][84]. Dark Stars provide a route to form objects of ∼ 10 3 M at much earlier times around 10 6 years, falling in the category of SMBH seeds from Pop-III remnants [77]. ...
The classical equations of motion for an axion with potential possess quasi-stable, localized, oscillating solutions, which we refer to as "axion stars". We study, for the first time, collapse of axion stars numerically using the full non-linear Einstein equations of general relativity and the full non-perturbative cosine potential. We map regions on an "axion star stability diagram", parameterized by the initial ADM mass, , and axion decay constant, . We identify three regions of the parameter space: i) long-lived oscillating axion star solutions, with a base frequency, , modulated by self-interactions, ii) collapse to a BH and iii) complete dispersal due to gravitational cooling and interactions. We locate the boundaries of these three regions and an approximate "triple point" . For below the triple point BH formation proceeds during winding (in the complex U(1) picture) of the axion field near the dispersal phase. This could prevent astrophysical BH formation from axion stars with . For larger , BH formation occurs through the stable branch and we estimate the mass ratio of the BH to the stable state at the phase boundary to be within numerical uncertainty. We discuss the observational relevance of our findings for axion stars as BH seeds, which are supermassive in the case of ultralight axions. For the QCD axion, the typical BH mass formed from axion star collapse is .
... In this WIMP paradigm, particle and antiparticle populations of DM come with equal numbers. Gravitational collapse of such type of DM could create dark stars that oppose further gravitational collapse by radiation pressure [42][43][44]. However, these types of stars cannot exist anymore, as DM annihilations would have already lead to the depletion of the DM population and therefore to the extinction of these dark stars long time ago. ...
Theoretical models of self-interacting dark matter represent a promising answer to a series of open problems within the so-called collisionless cold dark matter (CCDM) paradigm. In case of asymmetric dark matter, self-interactions might facilitate gravitational collapse and potentially lead to formation of compact objects predominantly made of dark matter. Considering both fermionic and bosonic equations of state, we construct the equilibrium structure of rotating dark stars, focusing on their bulk properties, and comparing them with baryonic neutron stars. We also show that these dark objects admit the I-Love-Q universal relations, which link their moments of inertia, tidal deformabilities, and quadrupole moments. Finally, we prove that stars built with a dark matter equation of state are not compact enough to mimic black holes in general relativity, thus making them distinguishable in potential events of gravitational interferometers.
... The pervasive and persistent injection of energy due to the presence of annihilating dark matter is expected to affect star formation and evolution [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], galaxy formation [25][26][27][28], and the ionisation history of the early Universe [29][30][31][32][33]. These effects may be difficult to detect if the canonical annihilation cross section is assumed ( σv = 3 × 10 −26 cm 3 s −1 ). ...
The existence of substructure in halos of annihilating dark matter would be expected to substantially boost the rate at which annihilation occurs. Ultracompact minihalos of dark matter (UCMHs) are one of the more extreme examples of this. The boosted annihilation can inject significant amounts of energy into the gas of a galaxy over its lifetime. Here we determine the impact of the boost factor from UCMH substructure on the heating of galactic gas in a Milky Way-type galaxy, by means of N-body simulation. If of the dark matter exists as UCMHs, the corresponding boost factor can be of order . For reasonable values of the relevant parameters (annihilation cross section , dark matter mass 100 GeV, 10% heating efficiency), we show that the presence of UCMHs at the 0.1% level would inject enough energy to eject significant amounts of gas from the halo, potentially preventing star formation within 1 kpc of the halo centre.
... New astrophysical objects that have not yet been experimentally detected could be discovered, such as those composed of dark matter, known as dark stars [18,19]. An interesting work that analyzes the emission of gravitational waves in alternative theories of compact binary systems can be reviewed in [20]. ...
In this work, we investigate head-on collisions of -boson stars, potential candidates for dark matter compact objects. We begin with a review of the general properties and features of these stars, leveraging results from prior studies to analyze the gravitational wave signals generated by such collisions. Considering a maximum distance of 100 Mpc for potential events, we identify the range of masses and scalar field frequencies for these stars that would render the gravitational waves detectable by current gravitational wave observatories. Additionally, we process the resulting signals to generate simulated observatory images, highlighting their similarities and differences compared to those produced by black hole collisions.
... By modifying the thermal profile near the hydrogen-burning core, slight changes in the main sequence turnoff can occur [14], and the main sequence lifetime can be significantly reduced [15]. If the dark matter χ self-annihilates, far fewer particles can be accumulated, but the effects on stellar energetics can be even more drastic, injecting 2m χ of heat per annihilation [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32], leading to changes in the core structure. ...
Capture and annihilation of weakly interacting massive particle (WIMP)-like dark matter in red giant stars can lead to faster-than-expected ignition of the helium core, and thus a lower tip of the red giant branch (TRGB) luminosity. We use data to place constraints on the dark matter-nucleon cross section using 22 globular clusters with measured TRGB luminosities, and place projections on the sensitivity resulting from 161 clusters with full phase space distributions observed by . Although limits remain weaker than those from Earth-based direct detection experiments, they represent a constraint that is fully independent of dark matter properties in the solar neighborhood, probing its properties across the entire Milky Way galaxy. Based on our findings, it is likely that the use of the TRGB as a standard candle in H 0 measurements is very robust against the effects of dark matter.
Published by the American Physical Society 2024
... The formation of SMBHs is a particularly intriguing question, with several promising pathways suggested: remnants of Population III (Pop III) stars (Bromm & Loeb 2003); mergers in nuclear star clusters (Gürkan et al. 2004;Portegies Zwart et al. 2004;Natarajan 2021); direct collapse (DC) of pregalactic gas disks where fragmentation and star formation are suppressed (Begelman et al. 2006;Lodato & Natarajan 2006); or dark stars powered by dark matter annihilation (Spolyar et al. 2008). There are two promising avenues to distinguish between various theoretical models. ...
Although supermassive black holes (SMBHs) reside in the heart of virtually every massive galaxy, it remains debated whether dwarf galaxies commonly host SMBHs. Because low-mass galaxies may retain memory of the assembly history of their black holes (BHs), probing the BH occupation fraction of local dwarf galaxies might offer insights into the growth and seeding mechanisms of the first BHs. In this work, we exploit the Western half of the eROSITA all-sky survey (covering 20,000 deg ² ) and compile a catalog of accreting SMBHs in local ( D < 200 Mpc) dwarf galaxies. Cleaning our sample from X-ray background sources, X-ray binaries, and ultraluminous X-ray sources, we identify 74 active galactic nucleus (AGN)–dwarf galaxy pairs. Using this large and uniform sample, we derive the luminosity function of the dwarf galaxy AGN, fitting it with a power-law function and obtaining d N / d L X = ( 15.9 ± 2.2 ) × L X − 1.63 ± 0.05 . Measuring the offset between the dwarf galaxies' centroids and the X-ray sources, we find that ≈50% of the AGN are likely off-nuclear, in agreement with theoretical predictions. We compare the BH-to-stellar mass relation of our sample with the local and high-redshift relations, finding that our sources better adhere to the former, which suggests that local AGN across different mass scales undergo similar growth histories. Finally, we compare our sources with semianalytical models: while our sample’s shallowness prevents distinguishing between different seeding models, we find that the data favor models that keep SMBHs in dwarf galaxies active at a moderate rate, motivating model improvement by comparison to AGN in the dwarf galaxy regime.
... On the other hand, compact stars serve as unique celestial laboratories, offering an extreme environment to investigate the interactions between dark matter (DM) and Standard Model (SM) particles. As DM traverses through a star, it will scatter with the stellar components, leading to the capture and impacting stellar evolution [6][7][8][9][10][11][12]. The investigations of DM properties through compact astrophysical objects have attracted increasing interest (see, e.g., Refs. ...
Because of the dense environment, neutron stars (NSs) can serve as an ideal laboratory for studying the interactions between dark matter (DM) and ordinary matter. In the process of DM capture, deep inelastic scattering may dominate over elastic scattering, especially for the DM with a large momentum transfer. In this work, we calculate DM-nucleon deep inelastic scattering via a vector mediator and estimate its contribution to the capture rate. Using the surface temperature of the NSs, we derive the exclusion limits for the DM-nucleon scattering cross section in the mass range 1 GeV < m χ < 10 5 GeV . We find the bounds for DM with the mass ≳ 1 GeV can be changed several times after including the deep inelastic scattering contribution.
Published by the American Physical Society 2024
... center [20]. Furthermore, it is possible that upon the creation of the NS, DM is inherited from the progenitor star [21][22][23]. In particular, BNS systems could have a relatively high amount of DM, since they are old systems that went through several stages of stellar evolution and the joint gravitational pull of the binary traps more DM particles in comparison to an isolated NS [24]. ...
If dark matter (DM) accumulates inside neutron stars (NS), it changes their internal structure and causes a shift of the tidal deformability from the value predicted by the dense-matter equation of state (EOS). In principle, this shift could be observable in the gravitational-wave (GW) signal of binary neutron star (BNS) mergers. We investigate the effect of fermionic, non-interacting DM when observing a large number of GW events from DM-admixed BNSs with the precision of the proposed Einstein telescope (ET). Specifically, we study the impact on the recovery of the baryonic EOS and whether DM properties can be constrained. For this purpose, we create event catalogues of BNS mock events with DM fraction up to 1%, from which we reconstruct the posterior uncertainties with the Fisher matrix approach. Using this data, we perform joint Bayesian inference on the baryonic EOS, DM particle mass, and DM particle fraction in each event. Our results reveal that when falsely ignoring DM effects, the EOS posterior is biased towards softer EOSs, though the offset is rather small. Further, we find that within our assumptions of our DM model and population, ET will likely not be able to test the presence of DM in BNSs, even when combining many events and adding Cosmic Explorer (CE) to the next-generation detector network. Likewise, the potential constraints on the DM particle mass will remain weak because of degeneracies with the fraction and EOS.
... Neutralino has appeared as a primary candidate among the potential explanations for the principal constituent and origin of DM. It is classified within the group of the lightest supersymmetric particles [5,6]. The investigation by Hadjimichef et al. [7] proposed a novel DM-based model for modeling ultra-dense stellar configurations, including white dwarfs, neutron stars (NS), and black holes. ...
In this manuscript, we investigate the possibility of constructing anisotropic dark matter compact stars motivated by the Einasto density profile. This work develops analytical solutions for an anisotropic fluid sphere within the framework of the well-known Adler-Finch-Skea metric. This toy model incorporates an anisotropic fluid distribution that includes a dark matter component. We use the minimal geometric deformation scheme within the framework of gravitational decoupling to incorporate anisotropy into the pressure profile of the stellar system. In this context, we model the temporal constituent of the -field sector to characterize the contribution of dark matter within the gravitational matter source. We present an alternative approach to studying anisotropic self-gravitating structures. This approach incorporates additional field sources arising from gravitational decoupling, which act as the dark component. We explicitly verify whether the proposed model satisfies all the requirements for describing realistic compact structures in detail. We conclude that the modeling of the Einasto density model with the Adler-Finch-Skea metric gives rise to the formation of well-behaved and viable astrophysical results that can be employed to model the dark matter stellar configurations.
... On the other hand, compact stars serve as unique celestial laboratories, offering an extreme environment to investigate the interactions between dark matter (DM) and Standard Model (SM) particles. As DM traverses through a star, it will scatter with the stellar components, leading to the capture and impacting stellar evolution [6][7][8][9][10][11][12]. The investigations of DM properties through compact astrophysical objects have attracted increasing interest (see e.g. ). ...
Due to the dense environment, neutron stars (NSs) can serve as an ideal laboratory for studying the interactions between dark matter (DM) and ordinary matter. In the process of DM capture, deep inelastic scattering may dominate over elastic scattering, especially for the DM with a large momentum transfer. In this work, we calculate DM-nucleon deep inelastic scattering via a vector mediator and estimate its contribution to the capture rate. Using the surface temperature of the NSs, we derive the exclusion limits for the DM-nucleon scattering cross section in the mass range, . We find the bounds for DM with the mass 1 GeV can be changed several times after including the deep inelastic scattering contribution.
... The "Pop III.1" SMBH formation model (Banik et al. 2019;Singh et al. 2023) invokes the physical mechanism of dark matter annihilation changing the structure of primordial protostars (Spolyar et al. 2008;Natarajan et al. 2009;Rindler-Daller et al. 2015) allowing efficient accretion of the baryonic content of their minihalos to become supermassive stars with masses of ∼10 5 M e , which then collapse to SMBHs. However, only the first minihalos to form in each local region of the Universe, i.e., being pristine and undisturbed by external feedback, are Pop III.1 sources and undergo this evolution. ...
We report the first results from a deep near-infrared campaign with the Hubble Space Telescope to obtain late-epoch images of the Hubble Ultra Deep Field, 10–15 yr after the first epoch data were obtained. The main objectives are to search for faint active galactic nuclei (AGN) at high redshifts by virtue of their photometric variability and measure (or constrain) the comoving number density of supermassive black holes (SMBHs), n SMBH , at early times. In this Letter, we present an overview of the program and preliminary results concerning eight objects. Three variables are supernovae, two of which are apparently hostless with indeterminable redshifts, although one has previously been recorded as a z ≈ 6 object precisely because of its transient nature. Two further objects are clear AGN at z = 2.0 and 3.2, based on morphology and/or infrared spectroscopy from JWST. Three variable targets are identified at z = 6–7 that are also likely AGN candidates. These sources provide a first measure of n SMBH in the reionization epoch by photometric variability, which places a firm lower limit of 3 × 10 ⁻⁴ cMpc ⁻³ . After accounting for variability and luminosity incompleteness, we estimate n SMBH ≳ 8 × 10 ⁻³ cMpc ⁻³ , which is the largest value so far reported at these redshifts. This SMBH abundance is also strikingly similar to estimates of n SMBH in the local Universe. We discuss how these results test various theories for SMBH formation.
... By modifying the thermal profile near the hydrogen-burning core, slight changes in the main sequence turnoff can occur [14], and the main sequence lifetime can be significantly reduced [15]. If the dark matter χ self-annihilates, far fewer particles can be accumulated, but the effects on stellar energetics can be even more drastic, injecting 2m χ of heat per annihilation [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32], leading to changes in the core structure. ...
Capture and annihilation of WIMP-like dark matter in red giant stars can lead to faster-than-expected ignition of the helium core, and thus a lower tip of the red giant branch (TRGB) luminosity. We use Gaia data to place constraints on the dark matter-nucleon cross section using 22 globular clusters with measured TRGB luminosities, and place projections on the sensitivity resulting from 161 clusters with full phase space distributions observed by Gaia. Although limits remain weaker than those from Earth-based direct detection experiments, they represent a constraint that is fully independent of dark matter properties in the Solar neighbourhood, probing its properties across the entire Milky Way galaxy. Based on our findings, it is likely that the use of the TRGB as a standard candle in measurements is very robust against the effects of dark matter.
... The formation of SMBHs is a particularly intriguing question, with several promising pathways suggested: remnants of Population III stars (Bromm & Loeb 2003); mergers in nuclear star clusters (Portegies Zwart et al. 2004;Gürkan et al. 2004;Natarajan 2021); direct collapse of pre-galactic gas disks where fragmentation and star formation are suppressed (Lodato & Natarajan 2006;Begelman et al. 2006); or dark stars powered by dark matter annihilation (Spolyar et al. 2008). There are two promising avenues to distinguish between various theoretical models. ...
Although supermassive black holes (SMBHs) reside in the heart of virtually every massive galaxy, it remains debated whether dwarf galaxies also commonly host SMBHs. Because low-mass galaxies may retain a memory of the assembly history of their black holes, probing the black hole occupation fraction of local dwarf galaxies might offer insights into the growth and seeding mechanisms of the first black holes. In this work, we exploit the Western half of the eROSITA all-sky survey (covering ) and compile a catalog of accreting SMBHs in local (~Mpc) dwarf galaxies. After cleaning our sample from cosmic X-ray background sources, X-ray binaries, and ultraluminous X-ray sources, we identify 74 AGN-dwarf galaxy pairs. Using this large and uniform sample, we derive a luminosity function of dwarf galaxy AGN, fitting it with a power law function and obtaining . Measuring the offset between the centroid of dwarf galaxies and the X-ray sources, we find that about of the AGN are likely off-nuclear, in agreement with theoretical predictions. We also compare the black hole-to-stellar mass relation of the AGN in our sample with the local and high-redshift relations, finding that our sources better adhere to the former. This suggests that local AGN across different mass scales underwent a similar growth history. Finally, we compare our sources with semi-analytical models: while our sample is too shallow to distinguish between different seeding models, it favors a growth mechanism linked to the star-formation rate of the host galaxy.
... This standard picture of stellar evolution assumes that nuclear fusion is the only process capable of providing pressure support for the star. However, in the early Universe [1][2][3][4][5][6][7][8], or in regions very close to the Galactic Center [9][10][11][12], dark matter annihilation may provide a considerable additional energy source. In extreme cases, dark matter annihilation can cause stars to move backwards along the HR diagrams towards proto-stellar configurations (Hayashi track) that have extremely large radii and low temperatures compared to standard stars [11]. ...
We show that stars in the inner parsec of the Milky Way can be significantly affected by dark matter annihilation, producing population-level effects that are visible in a Hertzsprung-Russell (HR) diagram. We establish the dark HR diagram, where stars lie on a new stable with similar luminosities, but lower temperatures, than the standard main sequence. The dark matter density in these stars continuously replenishes, granting these stars immortality and solving multiple stellar anomalies. Upcoming telescopes could detect the dark main sequence, offering a new dark matter discovery avenue.
... Their annihilation products interact with the hydrogen and dump energy into the cloud. So you have a very strange new star we call a dark star (4). It has no fusion and is heated by dark matter. ...
... Normally, a 1 M e star must wait 12 Gyr to reach 10 L e ; a BH with an initial mass of 10 −10 M e could drive it to that luminosity in less than half the time. The dark star scenario has been evoked to explain these observations (Spolyar et al. 2008;Rindler-Daller et al. 2015), which are hypothetical stars containing WIMPs or self-interacting dark matter such as neutralino dark matter. On that note, we also wish to draw attention to numerous other works that have implemented candidate dark matter solutions into stellar evolution codes. ...
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.
... However, it is not realistic to assume that the dark matter will follow circular orbits and so calculations were performed (Spolyar et al. 2008, Bambi et al. 2009) in the case of radial orbits to check if (4) is a good approximation for non-circular cases and the results agreed. However, it is also not realistic to assume that the dark matter will follow purely radial orbits and so the validity of the adiabatic approximation was tested in numerical simulations (Jesseit et al. 2002) from which it was shown to be a good approximation even when the collapse time is roughly the same as the free-fall time, dependent on the potential. ...
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 present an analytic description of the spherically symmetric gravitational collapse of radiatively cooling gas clouds, which illustrates the mechanism by which radiative cooling induces gravitational instability at a characteristic mass scale determined by the microphysics of the gas. The approach is based on developing the density-temperature relationship of the gas into a full dynamical model. We convert the density-temperature relationship into a barotropic equation of state, based on which we develop a refined instability criterion and calculate the density and velocity profiles of the gas. From these quantities we determine the time-dependent mass infall rate onto the center of the cloud. This approach distinguishes the rapid, quasi-equilibrium contraction of a cooling gas core to high central densities from the legitimate instability this contraction establishes in the envelope. We explicate the model in the context of a primordial mini-halo cooled by molecular hydrogen, and then provide two further examples: a delayed collapse with hydrogen deuteride cooling and the collapse of an atomic cooling halo. In all three cases, we show that our results agree well with full hydrodynamical treatments.
We present an implementation of Pop III.1 seeding of supermassive black holes (SMBHs) in a theoretical model of galaxy formation and evolution to assess the growth of the SMBH population and the properties of the host galaxies. The model of Pop III.1 seeding involves SMBH formation at redshifts in dark matter minihaloes that are isolated from external radiative feedback, parametrized by isolation distance . Within a standard CDM cosmology, we generate dark matter haloes using the code pinocchio and seed them according to the Pop III.1 scenario, exploring values of from 50 to 100 kpc (proper distance). We consider two alternative cases of SMBH seeding: a halo mass threshold model in which all haloes are seeded with black holes; an all light seed model in which all haloes are seeded with low, stellar mass black holes. We follow the redshift evolution of the haloes, populating them with galaxies using the GAlaxy Evolution and Assembly theoretical model of galaxy formation, including accretion on SMBHs and related feedback processes. Here we present predictions for the properties of galaxy populations, focusing on stellar masses, star formation rates, and black hole masses. The local, metrics of occupation fraction as a function of the galaxy stellar mass, galaxy stellar mass function, and black hole mass function all suggest a constraint of kpc. We discuss the implications of this result for the Pop III.1 seeding mechanism.
We present updated constraints on dark matter models with momentum-dependent or velocity-dependent interactions with nuclei, based on direct detection and solar physics. We improve our previous treatment of energy transport in the solar interior by dark matter scattering, leading to significant changes in fits to many observables. Based on solar physics alone, DM with a spin-independent coupling provides the best fit to data, and a statistically satisfactory solution to the solar abundance problem. Once direct detection limits are accounted for however, the best solution is spin-dependent scattering with a reference cross-section of 10 cm (at a reference velocity of km s), and a dark matter mass of about 5 GeV.
We investigate the formation of high-redshift supermassive black holes (SMBHs) via the direct collapse of baryonic clouds, where the unwanted formation of molecular hydrogen is successfully suppressed by a Lyman-Werner (LW) photon background from relic particle decay. We improve on existing studies by dynamically simulating the collapse, accounting for the adiabatic contraction of the DM halo, as well as the in situ production of the LW photons within the cloud which reduce the impact of the cloud’s shielding. We find a viable parameter space where the decay of either some of the dark matter or all of a subdominant decaying species successfully allows direct collapse of the cloud to a SMBH.
Dark Matter (DM) can become captured, deposit annihilation energy, and hence increase the heat flow in exoplanets and brown dwarfs. Detecting such a DM-induced heating in a population of exoplanets in the inner kpc of the Milky Way thus provides potential sensitivity to the galactic DM halo parameters. We develop a Bayesian Hierarchical Model to investigate the feasibility of DM discovery with exoplanets and examine future prospects to recover the spatial distribution of DM in the Milky Way. We reconstruct from mock exoplanet datasets observable parameters such as exoplanet age, temperature, mass, and location, together with DM halo parameters, for representative choices of measurement uncertainty and the number of exoplanets detected. We find that detection of ℴ(100) exoplanets in the inner Galaxy can yield quantitative information on the galactic DM density profile, under the assumption of 10% measurement uncertainty. Even as few as ℴ(10) exoplanets can deliver meaningful sensitivities if the DM density and inner slope are sufficiently large. https://github.com/mariabenitocst/exoplanets
Context. The collapse of supermassive stars (SMSs) via the general-relativistic (GR) instability would provide a natural explanation for the existence of the most extreme quasars. The presence of dark matter in SMSs is thought to potentially impact their properties, in particular their mass at collapse. Dark matter might be made of weakly interacting massive particles (WIMPs) that can be captured by the gravitational potential well of SMSs due to the interaction with the baryonic gas, favouring high dark matter densities in the star’s core. The annihilation of WIMPs can provide fuel to support the star before H-burning ignition, favouring low densities of baryonic gas, long stellar lifetimes, and high final masses.
Aims. Here we estimate the impact of dark matter on the GR dynamical stability of rapidly accreting SMSs.
Methods. We added a dark matter term to the relativistic equation of adiabatic pulsations and applied it to hylotropic structures in order to determine the onset point of the GR instability. We considered both a homogeneous dark matter background and density profiles of the form ∝exp(− r ² / r χ ² ), typical for the case of WIMPs capture. The free choice of the central temperature in hylotropic models allowed us to consider SMSs fuelled by H-burning and by WIMP annihilation.
Results. We find that, in principle, the dark matter gravitational field can completely remove the GR instability. However, for SMSs fuelled by H-burning the dark matter densities required to stabilise the star against GR are orders of magnitude above the values that are expected for the dark matter background. In the case of WIMPs capture, where the required densities can be reached in the centre of the star, the high centralisation of the dark matter component prevents any effect on the GR instability. On the other hand, for SMSs fuelled by WIMP annihilation, we find that the low densities of baryonic gas inhibit the destabilising GR corrections, which shifts the stability limit by typically an order of magnitude towards higher masses. As long as central temperatures ≲10 ⁷ K are maintained by WIMP annihilation, the GR instability is reached only for stellar masses > 10 ⁶ M ⊙ .
Conclusions. Dark matter can impact the GR dynamical stability of SMSs only in the case of energetically significant WIMP annihilation. The detection of a SMS with mass > 10 ⁶ M ⊙ in an atomically cooled halo can be interpreted as evidence of WIMP annihilation in the star’s core.
Recent observations of the high-redshift universe have uncovered a significant number of active galactic nuclei, implying that supermassive black holes (SMBHs) would have to have been formed at much earlier times than expected. Direct collapse of metal-free gas clouds to SMBHs after recombination could help explain the early formation of SMBHs, but this scenario is stymied by the fragmentation of the clouds due to efficient molecular hydrogen cooling. We show that a subdominant population of tiny, evaporating primordial black holes, with significant clustering in some gas clouds, can heat the gas sufficiently so that molecular hydrogen is not formed, and direct collapse to black holes is possible even at high redshifts.
Standard stellar evolution models predict that black holes in the range of approximately 50−140M⊙ should not exist directly from stellar evolution. This gap appears because stars with masses between 100 and 240M⊙ are expected to undergo a pair instability supernova and leave behind no remnant, or a pulsational pair instability supernova and leave behind a remnant much smaller than their initial stellar mass. However, black holes have been discovered by the LIGO/Virgo collaboration within this mass range. In previous work [J. Ziegler and K. Freese, Filling the black hole mass gap: Avoiding pair instability in massive stars through addition of nonnuclear energy, Phys. Rev. D 104, 043015 (2021).], we used the stellar evolution code MESA to show that the addition of non-nuclear energy (such as from annihilation of dark matter) could alter the evolution of a 180M⊙ star so that the observed black holes could be produced from isolated stars. In this paper, we extend this analysis to stars of other masses, and find that sufficient amounts of non-nuclear energy can allow any star to avoid pair instability, and could produce a black hole of mass comparable to the initial stellar mass. In addition, we produce examples of the type of black hole initial mass function that can be produced from this mechanism. These illustrative examples suggest that adding non-nuclear energy to stars offers a way to fully close the mass gap.
The first stars are expected to form through molecular-hydrogen (H2) cooling, a channel that is especially sensitive to the thermal and ionization state of gas, and can thus act as a probe of exotic energy injection from decaying or annihilating dark matter (DM). Here, we use a toy halo model to study the impact of DM-sourced energy injection on the H2 content of the first galaxies, and thus estimate the threshold mass required for a halo to form stars at high redshifts. We find that currently allowed DM models can significantly change this threshold, producing both positive and negative feedback. In some scenarios, the extra heating of the gas raises the halo mass required for collapse, whereas in others, energy injection lowers the threshold by increasing the free-electron fraction and catalyzing H2 formation. The direction of the effect can be redshift-dependent. We also bracket the self-shielding uncertainties on the impact of the Lyman-Werner radiation from DM. Hence, exotic energy injection can both delay and accelerate the onset of star formation; we show how this can impact the timing of 21-cm signals at cosmic dawn. We encourage detailed simulation follow-ups in the most promising regions of parameter space identified in this work.
Dark Matter (DM) can become captured, deposit annihilation energy, and hence increase the heat flow in exoplanets and brown dwarfs. Detecting such a DM-induced heating in a population of exoplanets in the inner kpc of the Milky Way thus provides potential sensitivity to the galactic DM halo parameters. We develop a Bayesian Hierarchical Model to investigate the feasibility of DM discovery with exoplanets and examine future prospects to recover the spatial distribution of DM in the Milky Way. We reconstruct from mock exoplanet datasets observable parameters such as exoplanet age, temperature, mass, and location, together with DM halo parameters, for representative choices of measurement uncertainty and the number of exoplanets detected. We find that detection of exoplanets in the inner Galaxy can yield quantitative information on the galactic DM density profile, under the assumption of 10% measurement uncertainty. Even as few as exoplanets can deliver meaningful sensitivities if the DM density and inner slope are sufficiently large.
Various theoretical models predict the existence of exotic compact objects that can mimic the properties of black holes (BHs). Gravitational waves (GWs) from the mergers of compact objects have the potential to distinguish between exotic compact objects and BHs. The measurement of spin-induced multipole moments of compact objects in binaries provides a unique way to test the nature of compact objects. The observations of GWs by LIGO and Virgo have already put constraints on the spin-induced quadrupole moment, the leading order spin-induced moment. In this work, we develop a Bayesian framework to measure the spin-induced octupole moment, the next-to-leading order spin-induced moment. The precise measurement of the spin-induced octupole moment will allow us to test its consistency with that of Kerr BHs in GR and constrain the allowed parameter space for non-BH compact objects. For various simulated compact object binaries, we explore the ability of the LIGO and Virgo detector network to constrain the spin-induced octupole moment. We find that LIGO and Virgo at design sensitivity can constrain the symmetric combination of component spin-induced octupole moments of binary for dimensionless spin magnitudes ∼0.8. Further, we study the possibility of simultaneously measuring the spin-induced quadrupole and octupole moments. Finally, we perform this test on selected GW events reported in the third GW catalog. These are the first constraints on spin-induced octupole moment using full Bayesian analysis.
With the launch of JWST and other scheduled missions aimed at probing the distant Universe, we are entering a new promising era for high-z astronomy. One of our main goals is the detection of the first population of stars (Population III or Pop III stars), and models suggest that Pop III star formation is allowed well into the Epoch of Reionization (EoR), rendering this an attainable achievement. In this paper, we focus on our chance of detecting massive Pop IIIs at the moment of their death as Pair-Instability Supernovae (PISNe). We estimate the probability of discovering PISNe during the EoR in galaxies with different stellar masses (7.5 ≤ Log(M⋆/M⊙) ≤ 10.5) from six dustyGadget simulations of 50h−1 cMpc per side. We further assess the expected number of PISNe in surveys with JWST/NIRCam and Roman/WFI. On average, less than one PISN is expected in all examined JWST fields at z ≃ 8 with Δz = 1, and O(1) PISN may be found in a ∼1 deg2 Roman field in the best-case scenario, although different assumptions on the Pop III IMF and/or Pop III star-formation efficiency can decrease this number substantially. Including the contribution from unresolved low-mass halos holds the potential for increased discoveries. JWST/NIRCam and Roman/WFI allow the detection of massive-progenitor (∼250 M⊙) PISNe throughout all the optimal F200W-F356W, F277W-F444W, and F158-F213 colors. PISNe are also predominantly located at the outskirts of their hosting haloes, facilitating the disentangling of underlying stellar emission thanks to the spatial-resolution capabilities of the instruments.
In this paper, we introduce an anisotropic model using a dark matter (DM) density profile in Einstein–Gauss–Bonnet (EGB) gravity using a gravitational decoupling method introduced by Ovalle (Phys Rev D 95:104019, 2017), which has provided an innovative approach for obtaining solutions to the EGB field equations for the spherically symmetric structure of stellar bodies. The Tolman and Finch–Skea (TFS) solutions of two metric potentials, g tt and g rr , have been used to construct the seed solution. Additionally, the presence of DM in DM halos distorts spacetime, causing perturbations in the g rr metric potential, where the quantity of DM is determined by the decoupling parameter β . The physical validity of the solution, along with stability and equilibrium analysis, has also been performed. Along with stability and equilibrium analysis, the solution’s physical validity has also been examined. Additionally, we have shown how both constants affect the physical characteristics of the solution. Using a M - R diagram, it has been described how the DM component and the GB constant affect the maximum permissible masses and their corresponding radii for various compact objects. Our model predicts the masses beyond the 2 M ⊙ and maximum radii 11 . 92 - 0.01 + 0.02 and 12 . 83 - 0.02 + 0.01 for larger value of α under density order 10 15 g / cm 3 and 10 14 g / cm 3 , respectively, while the radii become 11 . 96 - 0.01 + 0.01 and 12 . 81 - 0.02 + 0.01 for larger value of β .
Significance
In 2007, we proposed the idea of Dark Stars. The first phase of stellar evolution in the history of the universe may be Dark Stars (DS), powered by dark matter (DM) heating rather than by nuclear fusion. Although made almost entirely of hydrogen and helium from the Big Bang, they form at the centers of protogalaxies where there is a sufficient abundance of DM to serve as their heat source. They are very bright diffuse puffy objects and grow to be very massive. In fact, they can grow up to ten million solar masses with up to ten billion solar luminosities. In this paper, we show that the James Webb Space Telescope may have already discovered these objects.
With the launch of JWST and other scheduled missions aimed at probing the distant Universe, we are entering a new promising era for high-z astronomy. One of our main goals is the detection of the first population of stars (Population III or Pop III stars), and models suggest that Pop III star formation is allowed well into the Epoch of Reionization (EoR), rendering this an attainable achievement. In this paper, we focus on our chance of detecting massive Pop IIIs at the moment of their death as Pair-Instability Supernovae (PISNe). We estimate the probability of discovering PISNe during the EoR in galaxies with different stellar masses () from six dustyGadget simulations of cMpc per side. We further assess the expected number of PISNe in surveys with JWST/NIRCam and Roman/WFI. On average, less than one PISN is expected in all examined JWST fields, while PISNe may be found in a deg Roman field, with potential for increased discoveries when considering more optimistic choices for the Pop III initial mass function and formation efficiency , and when including the contribution of coarsely-resolved environments. JWST/NIRCam and Roman/WFI allow the detection of massive-progenitor ( ) PISNe throughout all the optimal F200W-F356W, F277W-F444W, and F158-F213 colors. PISNe are also predominantly located at the outskirts of their hosting haloes, facilitating the disentangling of underlying stellar emission thanks to the spatial-resolution capabilities of the instruments.
The assumption that in the early stage of the universe there existed turbulence of photons and plasma dragged by them can
explain the formation of galaxies plausibly. Using simple expressions to represent the decay law of the primordial turbulence,
the thermal history of gas at the pre-galactic stage is followed and the residual ionization degree of hydrogen is computed.
It is found that maximum temperatures attainable are about 104 °K for a wide range of heating parameters. This is because a kind of thermostat that keeps gas temperature below 104 °K operates: the increase of temperature above 104 °K prevented by the increase of the ionization degree and the resultant increase of cooling rate. Therefore, it can be concluded
that galaxies cannot be formed through the thermal instability due to the heating by the primordial turbulence.
We discuss the gamma-ray signal from dark matter annihilation in our Galaxy and in external objects, namely, the Large Magellanic Cloud, the Andromeda Galaxy (M31), and M87. We derive predictions for the fluxes in a low energy realization of the minimal supersymmetric standard model and compare them with current data from EGRET, CANGAROO-II, and HEGRA and with the capabilities of new-generation satellite-borne experiments, like GLAST, and ground-based Cerenkov telescopes, like VERITAS. We find fluxes below the level required to explain the possible indications of a γ-ray excess shown by CANGAROO-II (toward the galactic center) and HEGRA (from M87). As far as future experiments are concerned, we show that only the signal from the galactic center could be accessible to both satellite-borne experiments and to atmospheric Cerenkov telescopes (ACTs), even though this requires very steep dark matter density profiles.
Astrophysical consequences of the existence of any massive stable
neutral lepton, and of heavy stable neutrinos in particular, are
investigated. The extent to which heavy neutrinos may cluster
gravitationally is studied, and it is suggested that heavy neutrinos
might supply the dominant mass on large scales in galaxies and clusters
of galaxies. The collapse of a gas consisting of nonrelativistic
nondegenerate inert heavy neutrinos is analyzed, some specific
simplified cases of collapse in which the neutrinos are treated as test
particles are examined, and effects due to the self-gravity of the
neutrinos are discussed. It is found that the ratio of heavy neutrinos
to ordinary matter is preserved in any structures formed by
dissipationless collapse and that the heavy neutrinos may dominate the
total mass in such objects. Implications of these results are considered
for galaxy formation, the masses of galaxies and clusters, and stellar
structure and evolution.
The discovery of luminous quasars at redshift z ~ 6 indicates the presence of supermassive black holes (SMBHs) of mass ~109 M☉ when the universe was less than 1 billion years old. This finding presents several challenges for theoretical models because whether such massive objects can form so early in the ΛCDM cosmology, the leading theory for cosmic structure formation, is an open question. Furthermore, whether the formation process requires exotic physics such as super-Eddington accretion remains undecided. Here we present the first multiscale simulations that, together with a self-regulated model for the SMBH growth, produce a luminous quasar at z ~ 6.5 in the ΛCDM paradigm. We follow the hierarchical assembly history of the most massive halo in a ~3 Gpc3 volume and find that this halo of ~8 × 1012 M☉ forming at z ~ 6.5 after several major mergers is able to reproduce a number of observed properties of SDSS J1148+5251, the most distant quasar detected at z = 6.42 (Fan et al. 2003). Moreover, the SMBHs grow through gas accretion below the Eddington limit in a self-regulated manner owing to feedback. We find that the progenitors experience vigorous star formation (up to 104 M☉ yr-1) preceding the major quasar phase such that the stellar mass of the quasar host reaches 1012 M☉ at z ~ 6.5, consistent with observations of significant metal enrichment in SDSS J1148+5251. The merger remnant thus obeys a similar MBH-Mbulge scaling relation observed locally as a consequence of coeval growth and evolution of the SMBH and its host galaxy. Our results provide a viable formation mechanism for z ~ 6 quasars in the standard ΛCDM cosmology and demonstrate a common, merger-driven origin for the rarest quasars and the fundamental MBH-Mbulge correlation in a hierarchical universe.
Recent observations indicate that dark matter halos have flat central density profiles. Cosmological simulations with nonbaryonic dark matter, however, predict self-similar halos with central density cusps. This contradiction has lead to the conclusion that dark matter must be baryonic. Here it is shown that the dark matter halos of dwarf spiral galaxies represent a one-parameter family with self-similar density profiles. The observed global halo parameters are coupled with each other through simple scaling relations which can be explained by the standard cold dark matter model if one assumes that all the halos formed from density fluctuations with the same primordial amplitude. We find that the finite central halo densities correlate with the other global parameters. This result rules out scenarios where the flat halo cores formed subsequently through violent dynamical processes in the baryonic component. These cores instead provide important information on the origin and nature of dark matter in dwarf galaxies.
The paper analyzes the structure of fast shocks incident upon interstellar gas of ambient density from 10 to the 7th per cu cm, while focusing on the problems of formation and destruction of molecules and infrared emission in the cooling, neutral post shock gas. It is noted that such fast shocks initially dissociate almost all preexisting molecules. Discussion covers the physical processes which determine the post shock structure between 10 to the 4 and 10 to the 2 K. It is shown that the chemistry of important molecular coolants H2, CO, OH, and H2O, as well as HD and CH, is reduced to a relatively small set of gas phase and grain surface reactions. Also, the chemistry follows the slow conversion of atomic hydrogen into H2, which primarily occurs on grain surfaces. The dependence of this H2 formation rate on grain and gas temperatures is examined and the survival of grains behind fast shocks is discussed. Post shock heating and cooling rates are calculated and an appropriate, analytic, universal cooling function is developed for molecules other than hydrogen which includes opacities from both the dust and the lines.
We describe results from a fully self-consistent three-dimensional hydrodynamical simulation of the formation of one of the first stars in the Universe. In current models of structure formation, dark matter initially dominates, and pregalactic objects form because of gravitational instability from small initial density perturbations. As they assemble via hierarchical merging, primordial gas cools through ro-vibrational lines of hydrogen molecules and sinks to the center of the dark matter potential well. The high-redshift analog of a molecular cloud is formed. As the dense, central parts of the cold gas cloud become self-gravitating, a dense core of approximately 100 M (where M is the mass of the Sun) undergoes rapid contraction. At particle number densities greater than 10(9) per cubic centimeter, a 1 M protostellar core becomes fully molecular as a result of three-body H2 formation. Contrary to analytical expectations, this process does not lead to renewed fragmentation and only one star is formed. The calculation is stopped when optical depth effects become important, leaving the final mass of the fully formed star somewhat uncertain. At this stage the protostar is accreting material very rapidly (approximately 10(-2) M year-1). Radiative feedback from the star will not only halt its growth but also inhibit the formation of other stars in the same pregalactic object (at least until the first star ends its life, presumably as a supernova). We conclude that at most one massive (M 1 M) metal-free star forms per pregalactic halo, consistent with recent abundance measurements of metal-poor galactic halo stars.
The cosmological moduli problem is discussed in the framework of sequestered sector/anomaly-mediated supersymmetry (SUSY) breaking. In this scheme, the gravitino mass (corresponding to the moduli masses) is naturally 10 - 100 TeV, and hence the lifetime of the moduli fields can be shorter than . As a result, the cosmological moduli fields should decay before big-bang nucleosynthesis starts. Furthermore, in the anomaly-mediated scenario, the lightest superparticle (LSP) is the Wino-like neutralino. Although the large annihilation cross section means the thermal relic density of the Wino LSP is too small to be the dominant component of cold dark matter (CDM), moduli decays can produce Winos in sufficient abundance to constitute CDM. If Winos are indeed the dark matter, it will be highly advantageous from the point of view of detection. If the halo density is dominated by the Wino-like LSP, the detection rate of Wino CDM in Ge detectors can be as large as event/kg/day, which is within the reach of the future CDM detection with Ge detector. Furthermore, there is a significant positron signal from pair annihilation of Winos in our galaxy which should give a spectacular signal at AMS. Comment: 19 pages, 4 figures
We present a theoretical model for primordial star formation. First we describe the structure of the initial gas cores as virialized, quasi-hydrostatic objects in accord with recent high resolution numerical studies. The accretion rate can then be related to characteristic densities and temperatures that are set by the cooling properties of molecular hydrogen. We allow for rotation of the gas core, assuming angular momentum conservation inside the sonic point of the flow. In the typical case, most mass then reaches the star via an accretion disk. The structure of the inner region of this disk is described with the standard theory of viscous disks, but with allowance for the substantial energies absorbed in ionizing and dissociating the gas. The size of the protostar and its luminosity depend upon the accretion rate, the energetics of the accreting gas, and the ability of the radiation to escape from the stellar accretion shock. We combine these models for the infall rate, inner disk structure, and protostellar evolution to predict the radiation field that is the basis for radiative feedback processes acting against infall (Paper II). For realistic initial angular momenta, the photosphere of the protostar is much smaller and hotter than in the spherical case, leading to stronger radiative feedback at earlier stages in the evolution. In particular, once the star is older than its Kelvin-Helmholtz time, contraction towards the main sequence causes a rapid increase in ionizing and far-ultraviolet luminosity at masses ~30Msun in the fiducial case. Since the cores out of which the first stars formed were much more massive than 30Msun and since feedback is dynamically unimportant at lower masses, we conclude that the first stars should have had masses >~30Msun. Comment: 20 pages, Accepted to ApJ, some re-arrangement of text for improved clarity
Massive central objects affect both the structure and evolution of galactic nuclei. Adiabatic growth of black holes generates power-law central density profiles with logarithmic slopes in the range from ~1.5 to ~2.5, in good agreement with the profiles observed in the nuclei of galaxies fainter than visual magnitude -20. However the shallow nuclear profiles of bright galaxies require a different explanation. Binary black holes are an inevitable result of galactic mergers, and the ejection of stars by a massive binary displaces a mass of order the binary's own mass, creating a core or shallow power-law cusp. This model is at least crudely consistent with core sizes in bright galaxies. Uncertainties remain about the effectiveness of stellar- and gas-dynamical processes at inducing coalescence of binary black holes, and uncoalesced binaries may be common in low-density nuclei.
We use N-body simulations to investigate the structure of dark halos in the standard Cold Dark Matter cosmogony. Halos are excised from simulations of cosmologically representative regions and are resimulated individually at high resolution. We study objects with masses ranging from those of dwarf galaxy halos to those of rich galaxy clusters. The spherically averaged density profiles of all our halos can be fit over two decades in radius by scaling a simple ``universal'' profile. The characteristic overdensity of a halo, or equivalently its concentration, correlates strongly with halo mass in a way which reflects the mass dependence of the epoch of halo formation. Halo profiles are approximately isothermal over a large range in radii, but are significantly shallower than near the center and steeper than near the virial radius. Matching the observed rotation curves of disk galaxies requires disk mass-to-light ratios to increase systematically with luminosity. Further, it suggests that the halos of bright galaxies depend only weakly on galaxy luminosity and have circular velocities significantly lower than the disk rotation speed. This may explain why luminosity and dynamics are uncorrelated in observed samples of binary galaxies and of satellite/spiral systems. For galaxy clusters, our halo models are consistent both with the presence of giant arcs and with the observed structure of the intracluster medium, and they suggest a simple explanation for the disparate estimates of cluster core radii found by previous authors. Our results also highlight two shortcomings of the CDM model. CDM halos are too concentrated to be consistent with the halo parameters inferred for dwarf irregulars, and the predicted abundance of galaxy halos is larger than the observed abundance of galaxies.
We investigate the physical conditions for the growth of intermediate mass
seed black holes assumed to have formed from remnants of the first generation
of massive stars. We follow the collapse of high-sigma halos with Tvir > 1e4 K
using cosmological, smooth-particle hydrodynamic (SPH) simulations in the
standard LCDM model. During collapse of the parent halo the seed holes are
incorporated through mergers into larger systems and accrete mass from the
surrounding gas. We include a self-consistent treatment of star formation,
black hole accretion and associated feedback processes. Even under optimistic
assumptions for the seed black hole mass and for efficient merger rates, we
find that seed holes in halos M<1e10 Msun never reach the conditions for
critical Eddington growth. Most of the black hole growth in this regime is
determined by the initial mass and the merger rates. Critical accretion rates
are reached, albeit only after a significant delay, at the time of collapse
z~7) for 3-4 sigma halos of M~1e11 Msun. Our results imply M_BH = 5e6 Msun
(M_halo/1e11 Msun)^0.78 at the time of collapse. The required conditions of
Eddington growth to explain the build-up of supermassive black holes (~1e9
Msun), as implied by Sloan quasars at z>6, are therefore hard to meet in such a
scenario. Without a 'jump-start' these conditions may be only achieved in
extremely rare halos with M_halo > 1e13 Msun that collapsed before z~6. The
sub-Eddington regime in which black holes holes accrete at early time implies a
small contribution to the reionization by miniquasar but still sufficient to
cause appreciable heating of the IGM at z<15-18.
We derive the effects of DM decays and annihilations on structure formation. We consider moderately massive DM particles (sterile neutrinos and light DM), as they are expected to give the maximum contribution to heating and reionization. The energy injection from DM decays and annihilations produces both an enhancement in the abundance of coolants (H2 and HD) and an increase of gas temperature. We find that for all the considered DM models the critical halo mass for collapse, m_crit, is generally higher than in the unperturbed case. However, the variation of m_crit is small. In the most extreme case, i.e. considering light DM annihilations (decays) and halos virializing at redshift z_vir>10 (z_vir~10), m_crit increases by a factor ~4 (~2). In the case of annihilations the variations of m_crit are also sensitive to the assumed profile of the DM halo. Furthermore, we note that the fraction of gas which is retained inside the halo is substantially reduced (to ~40 per cent of the cosmic value), especially in the smallest halos, as a consequence of the energy injection by DM decays and annihilations.
In these lecture notes we review the current knowledge about the formation of
the first luminous objects. We start from the cosmological context of
hierarchical models of structure formation, and discuss the main physical
processes which are believed to lead to primordial star formation, i.e. the
cooling processes and the chemistry of molecules (especially H2) in a
metal-free gas. We then describe the techniques and results of numerical
simulations, which indicate that the masses of the first luminous objects are
likely to be much larger than that of present-day stars. Finally, we discuss
the scenario presented above, exposing some of the most interesting problems
which are currently being investigated, such as that of the feedback effects of
these objects.
Some dwarf galaxies have HI rotation curves that are completely dominated by a surrounding dark matter (DM) halo (e.g. Carignan & Freeman 1988). These objects represent ideal candidates for an investigation of the density structure of low-mass DM halos as the uncertainties resulting from the subtraction of the visible component are small, even in the innermost regions. Flores & Primack (1994) and Moore (1994) compared the observed DM rotation curves with the profiles, predicted from cosmological cold dark matter (CDM) calculations. They found an interesting discrepancy: whereas the calculations lead to a DM density distribution which diverges as ρ ∼ r −1 in the inner parts, the observed rotation curves indicate shallow DM cores which can be described by an isothermal density profile with finite central density.
The possibility of a flux of high energy neutrinos (100 MeV less than or equal to Enu less than or equal to 10GeV) from the Sun due to the annihilation within of particles which make up the galactic halo is considered. Specifically, if the halo consists of heavy neutrinos or stable supersymmetric particles with mass greater than or equal to 6GeV, halo particles will be trapped in the Sun and annihilate to produce a potentially observable high energy neutrino flux. Detailed estimates of this flux are provided for a variety of candidate halo particles: photinos, higgsinos, scalar neutrinos, heavy Dirac neutrinos, and heavy Majorana neutrinos. All of these can (for appropriate ranges of parameters) produce fluxes whose absolute value is at least comparable to atmospheric background. How the solar fluxes could be distinguished from the background is briefly discussed. The effect of trapped halo particles on the solar neutrino problem is also discussed.
The minimum mass that a virialized gas cloud must have in order to be able to cool in a Hubble time is computed, using a detailed treatment of the chemistry of molecular hydrogen. With a simple model for halo profiles, we reduce the problem to that of numerically integrating a system of chemical equations. The results agree well with numerically expensive three-dimensional simulations, and our approach has the advantage of being able to explore large regions of parameter space rapidly. The minimum baryonic mass Mb is found to be strongly redshift dependent, dropping from 106 M☉ at z ~ 15 to 5 × 103 M☉ at z ~ 100 as molecular cooling becomes effective. For z 100, Mb rises again, as cosmic microwave background photons inhibit H2 formation through the H- channel. Finally, for z 200, the H+2 channel for H2 formation becomes effective, driving Mb down toward Mb ~ 103 M☉. With a standard cold dark matter power spectrum with σ8 = 0.7, this implies that a fraction 10-3 of all baryons may have formed luminous objects by z = 30, which could be sufficient to reheat the universe.
We study the formation of the first generation of stars in the standard cold dark matter model. We use a very high resolution cosmological hydrodynamic simulation that achieves a dynamic range of ~1010 in length scale. With accurate treatment of atomic and molecular physics, including the effect of molecular line opacities and cooling by collision-induced continuum emission, it allows us to study the chemothermal evolution of primordial gas clouds to densities up to ρ ~ 2 × 10-8 g cm-3 (nH ~ 1016 cm-3) without assuming any a priori equation of state, an improvement of 6 orders of magnitude over previous three-dimensional calculations. We study the evolution of a primordial star-forming gas cloud in the cosmological simulation in detail. The cloud core becomes marginally unstable against chemothermal instability when the gas cooling rate is increased owing to three-body molecule formation. However, since the core is already compact at that point, runaway cooling simply leads to fast condensation to form a single protostellar seed. During the final dynamical collapse, small angular momentum material collapses faster than the rest of the gas and selectively sinks inward. Consequently, the central regions have little specific angular momentum, and rotation does not halt collapse. We, for the first time, obtain an accurate gas mass accretion rate within a 10 M☉ innermost region around the protostar. We carry out protostellar evolution calculations using the obtained accretion rate. The resulting mass of the first star when it reaches the zero-age main sequence is MZAMS ~ 100 M☉, and less (60 M☉) for substantially reduced accretion rates.
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.
We have performed a large set of high-resolution cosmological simulations using smoothed particle hydrodynamics to study the formation of the first luminous objects in the Lambda cold dark matter cosmology. We follow the collapse of primordial gas clouds in eight early structures and document the scatter in the properties of the first star-forming clouds. Our first objects span formation redshifts from z∼ 10 to ∼50 and cover an order of magnitude in halo mass. We find that the physical properties of the central star-forming clouds are very similar in all of the simulated objects despite significant differences in formation redshift and environment. This suggests that the formation path of the first stars is largely independent of the collapse redshift; the physical properties of the clouds have little correlation with spin, mass or assembly history of the host halo. The collapse of protostellar objects at higher redshifts progresses much more rapidly due to the higher densities, which accelerates the formation of molecular hydrogen, enhances initial cooling and shortens the dynamical time-scales. The mass of the star-forming clouds cover a broad range, from a few hundred to a few thousand solar masses, and exhibit various morphologies: some have disc-like structures which are nearly rotational supported; others form flattened spheroids; still others form bars. All of them develop a single protostellar ‘seed’ which does not fragment into multiple objects up to the moment that the central gas becomes optically thick to H2 cooling lines. At this time, the instantaneous mass accretion rate on to the centre varies significantly from object to object, with disc-like structures having the smallest mass accretion rates. The formation epoch and properties of the star-forming clouds are sensitive to the values of cosmological parameters.
We investigate the environmental impact of the first active galactic nuclei that may have formed ~150 Myr after the big bang in low-mass ~10^6 Msun minihaloes. Using Enzo, an adaptive-mesh refinement cosmological hydrodynamics code, we carry out three-dimensional simulations of the radiative feedback from `miniquasars' powered by intermediate-mass black holes. We follow the non-equilibrium multispecies chemistry of primordial gas in the presence of a point source of X-ray radiation, which starts shining in a rare high-sigma peak at z=21 and emits a power-law spectrum in the 0.2-10 keV range. We find that, after one Salpeter time-scale, the miniquasar has heated up the simulation box to a volume-averaged temperature of 2800 K. The mean electron and H2 fractions are now 0.03 and 4e-5: the latter is 20 times larger than the primordial value, and will delay the buildup of a uniform UV photodissociating background. The net effect of the X-rays is to reduce gas clumping in the IGM by as much as a factor of 3. While the suppression of baryonic infall lowers the gas mass fraction at overdensities delta in the range 20-2000, enhanced molecular cooling increases the amount of dense material at delta>2000. In many haloes within the proximity of our miniquasar the H2-boosting effect of X-rays is too weak to overcome heating, and the cold and dense gas mass actually decreases. We find little evidence for an entropy floor in gas at intermediate densities preventing gas contraction and H2 formation. Overall, the radiative feedback from X-rays enhances gas cooling in lower-sigma peaks that are far away from the initial site of star formation, thus decreasing the clustering bias of the early pregalactic population, but does not appear to dramatically reverse or promote the collapse of pregalactic clouds as a whole. (abridged)
Scalar neutrinos and massive Dirac neutrinos in the mass range 2–20 GeV have been proposed as candidates to provide the dark matter in the halo of our galaxy. If so, the particles are captured inthe Earth with an efficiency of 10−10 − 10−7. For Dirac neutrinos more massive than about 9 GeV and scalar neutrinos more massive than abour 12 GeV, enough are captured to produce an observable neutrino flux at the surface of the Earth (∼ 10−2 cm−2 s−1 for sneutrinos and ∼ 1.4 × 10−3 cm−2 s−1 for Dirac neutrinos), several orders of magnitude above atmospheric background and above what is observed. Hence stable scalar neutrinos of mass 12–20 GeV or Dirac neutrinos of mass 9–20 GeV cannot be the dominant component of the halo.
We re-evaluate the fluxes of cosmic ray antiprotons, positrons and gamma rays to be expected from the annihilations of relic particles in the galactic halo. We stress the importance of observational constraints on the possible halo density of relic particles, and specify their annihilation cross sections by the requirement that their cosmological density close the Universe. We use a Monte Carlo programme adapted to fit e+e− data to calculate the p̄, e+ and γ spectra for some supersymmetric relic candidates. We find significantly smaller p̄ fluxes than previously estimated, and conclude that present upper limits on cosmic ray p̄ and e+ do not exclude any range of sparticle masses. We discuss the prospects for possible future constraints on sparticles from cosmic γ rays.
This biennial Review summarizes much of particle physics. Using data from previous editions, plus 2633 new measurements from 689 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors, probability, and statistics. Among the 110 reviews are many that are new or heavily revised including those on CKM quark-mixing matrix, Vud & Vus, Vcb & Vub, top quark, muon anomalous magnetic moment, extra dimensions, particle detectors, cosmic background radiation, dark matter, cosmological parameters, and big bang cosmology.
A booklet is available containing the Summary Tables and abbreviated versions of some of the other sections of this full Review. All tables, listings, and reviews (and errata) are also available on the Particle Data Group website: http://pdg.lbl.gov.
The quasi-static contraction of primordial stars composed of pure hydrogen and helium gas is studied by following numerically the evolution of a star of five solar masses from the end of protostellar accretion to the onset of hydrogen burning. Although the protostellar core of this mass is radiatively stable and undergoing nonhomologous contraction, its large surface area and luminosity force the star to a partially convective, homologously contracting state within only 100 yr. Deuterium later ignites at an off-center temperature maximum but fails to produce interior convection. The star follows a conventional premain sequence track in the HR diagram, reaching the ZAMS after 1.2 million yr, with a luminosity of 880 solar luminosities and a radius of 1.2 solar radii.
We show that if our galactic halo were to consist of scalar or Dirac neutrinos with mass greater than ~12 GeV, capture by the Earth and subsequent annihilation would yield a large flux of neutrinos at the surface which could be seen in proton-decay detectors. The luminosity of Uranus provides comparable constraints. Capture in the Sun can yield supplementary information, with detectable signals possible for masses as low as 6 GeV for both Dirac and Majorana neutrinos, scalar neutrinos, and photinos. We discuss in detail the question of evaporation, on which our results and others depend sensitively. We suggest one method of approximating evaporation rates from the Earth and Sun and discuss potential problems with earlier estimates. Finally, we describe how particles which avoid these constraints may still be detectable by bolometric neutrino detectors and isolate a new method to remove backgrounds to this signal in such detectors.
It is pointed out that the magnetosphere of Jupiter is in many respects quite different from that of the earth. The energy required to drive the Jovian magnetosphere is apparently extracted from Jupiter's rotational energy rather than from the solar wind. Jupiter is a strong source of energetic charged particles which can be detected as far away as the orbit of Mercury. The structure and dynamics of the energetic particle distribution in the inner magnetosphere is discussed, taking into account observations, transport and losses in the inner magnetosphere, satellite interactions, and electron synchrotron radiation. The subsolar hemisphere is considered, giving attention to particle fluxes in the subsolar magnetosphere, conditions in the middle magnetosphere, and the characteristics of the outer magnetosphere. A description of the predawn magnetosphere is also provided.
The formation of the first stars and quasars marks the transformation of the
universe from its smooth initial state to its clumpy current state. In popular
cosmological models, the first sources of light began to form at redshift 30
and reionized most of the hydrogen in the universe by redshift 7. Current
observations are at the threshold of probing the hydrogen reionization epoch.
The study of high-redshift sources is likely to attract major attention in
observational and theoretical cosmology over the next decade.
The evolution of collapsing metal free protostellar clouds is investigated for various masses and initial conditions. We perform hydrodynamical calculations for spherically symmetric clouds taking account of radiative transfer of the molecular hydrogen lines and the continuum, as well as of chemistry of the molecular hydrogen. The collapse is found to proceed almost self-similarly like Larson-Penston similarity solution. In the course of the collapse, efficient three-body processes transform atomic hydrogen in an inner region of \sim 1 M_{\sun} entirely into molecular form. However, hydrogen in the outer part remains totally atomic although there is an intervening transitional layer of several solar masses, where hydrogen is in partially molecular form. No opaque transient core is formed although clouds become optically thick to H collision-induced absorption continuum, since H dissociation follows successively. When the central part of the cloud reaches stellar densities (), a very small hydrostatic core (\sim 5 \times 10^{-3} M_{\sun}) is formed and subsequently grows in mass as the ambient gas accretes onto it. The mass accretion rate is estimated to be 3.7 \times 10^{-2} M_{\sun} {\rm yr^{-1}} (M_{\ast}/M_{\sun})^{-0.37}, where is instantaneous mass of the central core, by using a similarity solution which reproduces the evolution of the cloud before the core formation. Comment: 20 pages, 5 Postscript figures, uses AAS LaTeX
The question of the nature of the dark matter in the Universe remains one of the most outstanding unsolved problems in basic science. One of the best motivated particle physics candidates is the lightest supersymmetric particle, assumed to be the lightest neutralino - a linear combination of the supersymmetric partners of the photon, the Z boson and neutral scalar Higgs particles. Here we describe DarkSUSY, a publicly-available advanced numerical package for neutralino dark matter calculations. In DarkSUSY one can compute the neutralino density in the Universe today using precision methods which include resonances, pair production thresholds and coannihilations. Masses and mixings of supersymmetric particles can be computed within DarkSUSY or with the help of external programs such as FeynHiggs, ISASUGRA and SUSPECT. Accelerator bounds can be checked to identify viable dark matter candidates. DarkSUSY also computes a large variety of astrophysical signals from neutralino dark matter, such as direct detection in low-background counting experiments and indirect detection through antiprotons, antideuterons, gamma-rays and positrons from the Galactic halo or high-energy neutrinos from the center of the Earth or of the Sun. Here we describe the physics behind the package. A detailed manual will be provided with the computer package. Comment: 35 pages, no figures
We review recent theoretical results on the formation of the first stars in the universe, and emphasize related open questions. In particular, we discuss the initial conditions for Population III star formation, as given by variants of the cold dark matter cosmology. Numerical simulations have investigated the collapse and the fragmentation of metal-free gas, showing that the first stars were predominantly very massive. The exact determination of the stellar masses, and the precise form of the primordial initial mass function, is still hampered by our limited understanding of the accretion physics and the protostellar feedback effects. We address the importance of heavy elements in bringing about the transition from an early star formation mode dominated by massive stars, to the familiar mode dominated by low mass stars, at later times. We show how complementary observations, both at high redshifts and in our local cosmic neighborhood, can be utilized to probe the first epoch of star formation.
We consider particle decays during the cosmic dark ages with two aims: (1) to
explain the high optical depth reported by WMAP, and (2) to provide new
constraints to the parameter space for decaying particles. We delineate the
decay channels in which most of the decay energy ionizes and heats the IGM gas
(and thus affects the CMB), and those in which most of the energy is carried
away -- e.g. photons with energies 100 keV < E < 1 TeV -- and thus appears as a
contribution to diffuse x-ray and gamma-ray backgrounds. The new constraints to
the decay-particle parameters from the CMB power spectrum thus complement those
from the cosmic X-ray and gamma-ray backgrounds. Although decaying particles
can indeed produce an optical depth consistent with that reported by WMAP, in
so doing they produce new fluctuations in the CMB temperature/polarization
power spectra. For decay lifetimes less than the age of the Universe, the
induced power spectra generally violate current constraints, while the power
spectra are usually consistent if the lifetime is longer than the age of the
Universe.
If cold dark matter is present at the galactic center, as in current models of the dark halo, it is accreted by the central black hole into a dense spike. Particle dark matter then annihilates strongly inside the spike, making it a compact source of photons, electrons, positrons, protons, antiprotons, and neutrinos. The spike luminosity depends on the density profile of the inner halo: halos with finite cores have unnoticeable spikes, while halos with inner cusps may have spikes so bright that the absence of a detected neutrino signal from the galactic center already places interesting upper limits on the density slope of the inner halo. Future neutrino telescopes observing the galactic center could probe the inner structure of the dark halo, or indirectly find the nature of dark matter. Comment: 4 pages, 5 figures
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