Formation Of Massive Black Holes Research Articles

The Scale of Stellar Yields: Implications of the Measured Mean Iron Yield of Core Collapse Supernovae

The scale of α-element yields is difficult to predict from theory because of uncertainties in massive star evolution, supernova physics, and black hole formation, and it is difficult to constrain empirically because the impact of higher yields can be compensated by greater metal loss in galactic winds. We use a recent measurement of the mean iron yield of core collapse supernovae (CCSN) by Rodriguez et al., y¯Fecc=0.058±0.007M⊙ , to infer the scale of α-element yields by assuming that the plateau of [α/Fe] abundance ratios observed in low-metallicity stars represents the yield ratio of CCSN. For a plateau at [α/Fe]cc = 0.45, we find that the population-averaged yields of O and Mg are about equal to the solar abundance of these elements, logyOcc/ZO,⊙=logyMgcc/ZMg,⊙=−0.01±0.1 , where yXcc is the mass of element X produced by massive stars per unit mass of star formation. The inferred O and Fe yields agree with predictions of the Sukhbold et al. CCSN models assuming their Z9.6+N20 neutrino-driven engine, a scenario in which many progenitors with M < 40M ⊙ implode to black holes rather than exploding. The yields are lower than assumed in many models of the galaxy mass–metallicity relation, reducing the level of outflows needed to match observed abundances. Our one-zone chemical evolution models with η=Ṁout/Ṁ*≈0.6 evolve to solar metallicity at late times. By further requiring that models reach [α/Fe] ≈ 0 at late times, we infer a Hubble-time integrated Type Ia supernova rate of 1.1×10−3M⊙−1 , compatible with estimates from supernova surveys.

An Enhanced Massive Black Hole Occupation Fraction Predicted in Cluster Dwarf Galaxies

The occupation fraction of massive black holes (MBHs) in low mass galaxies offers interesting insights into initial black hole seeding mechanisms and their mass assembly history, though disentangling these two effects remains challenging. Using the {Romulus} cosmological simulations we examine the impact of environment on the occupation fraction of MBHs in low mass galaxies. Unlike most modern cosmological simulations, {Romulus} seeds MBHs based on local gas properties, selecting dense (n&gt;3 cm^-3, 15 times the threshold for star formation), pristine (Z&lt;3e-4 Zsol), and rapidly collapsing regions in the early Universe as sites to host MBHs without assuming anything about MBH occupation as a function of galaxy stellar mass, or halo mass, {}. The simulations predict that dwarf galaxies with M&lt;1e9 Msol in cluster environments are ~2 times more likely to host a MBH compared to those in the field. The predicted occupation fractions are remarkably consistent with those of nuclear star clusters. Across cluster and field environments, dwarf galaxies with earlier formation times are more likely to host a MBH. Thus, while the MBH occupation function is similar between cluster and field environments at high redshift (z&gt;3), a difference arises as late-forming dwarfs – which do not exist in the cluster environment – begin to dominate in the field and pull the MBH occupation fraction down for low mass galaxies. Additionally, prior to in-fall some cluster dwarfs are similar to progenitors of massive, isolated galaxies, indicating that they might have grown to higher masses had they not been impeded by the cluster environment. While the population of MBHs in dwarf galaxies is already widely understood to be important for understanding MBH formation, this work demonstrates that environmental dependence is important to consider as future observations search for low mass black holes in dwarf galaxies.

Formation of Massive Black Holes with M = (103–108) M ⊙ at Pre-quasar Epochs through Hoyle–Lyttleton–Bondi Accretion of Self-interacting Dark Matter onto a Moving Seed

The presence of supermassive black holes with M ∼ 109 M ⊙ hosted by the luminous quasars at cosmological redshift z ≥ 6 is still an open problem in astrophysical cosmology. Here we study the formation of massive black holes at high redshift (z ≫ 7) through Hoyle–Lyttleton–Bondi accretion of self-interacting dark matter (SIDM) onto a 20 M ⊙ seed black hole moving with a velocity ∼100 km s−1 inside the short, mean-free path region of an SIDM halo. We consider observational constraints on a specific SIDM cross section, σ/m dm = (0.1–5) cm2 g−1. Formation timescale of massive black holes with M = (103–108) M ⊙ is calculated for the universal Navarro–Frenk–White (NFW) profile, singular isothermal sphere (SIS), other power-law profiles with a cusp index 2.19 ≤ γ ≤ 2.5 of accreted dark matter, and modified-core isothermal profiles. The ambient sound speed is taken as C s = (10–100) km s−1. It is found that an NFW profile with halo concentration C = 4.75–32.58 estimated at z = 20 and 30 for halo masses M 200 = (1012–1014) M ⊙ favors formation of massive black holes with M = (103–108) M ⊙ at high redshift, well before quasar epoch. In this profile, these black holes grow within timescales (0.1–69) Myr at z = 16–20. For the SIS profile, the black hole formation timescales are short compared to NFW. For power-law profiles, massive black holes with M = (106–108) M ⊙ grow within a few tens to 100 Myr (z = 5–30). For modified-core isothermal profiles, the timescale of massive black hole formation is in the range (0.79–464.08) Myr (z = 8–30).

Direct Formation of Massive Black Holes via Dynamical Collapse in Metal-enriched Merging Galaxies at z ∼ 10: Fully Cosmological Simulations

We present the results of the first fully cosmological hydrodynamical simulations studying the merger-driven model for massive black hole (BH) seed formation via direct collapse. Using the zoom-in technique as well as particle splitting, we achieve a final spatial resolution of 2 pc. We show that the major merger of two massive galaxies at redshift z ∼ 8 results in the formation of a nuclear supermassive disk (SMD) of only 4 pc in radius, owing to a prodigious gas inflow sustained at 100–1000 M ⊙ yr−1. The core of the merger remnant is metal-rich, well above solar abundance, and the SMD reaches a gaseous mass of 3 × 108 M ⊙ in less than a million years after the merger, despite a concurrent prominent nuclear starburst. Dynamical heating as gas falls into the deepest part of the potential well, and heating and stirring by supernova blastwaves, generate a turbulent multiphase interstellar medium, with a gas velocity dispersion exceeding 100 km s−1. As a result, only moderate fragmentation occurs in the inner 10–20 pc, despite the temperature falling below 1000 K. The SMD is Jeans-unstable as well as bar-unstable and will collapse further adiabatically, becoming warm and ionized. We show that the SMD, following inevitable contraction, will become general-relativistic-unstable and directly form a supermassive BH of mass in the range 106–108 M ⊙, essentially skipping the stage of BH seed formation. These results confirm that mergers between the most massive galaxies at z ∼ 8–10 can naturally explain the rapid emergence of bright high-redshift quasars.

Magnetic fields catalyse massive black hole formation and growth

ABSTRACT Large-scale magnetic fields in the nuclear regions of protogalaxies can promote the formation and early growth of supermassive black holes (SMBHs) by direct collapse and magnetically boosted accretion. Turbulence associated with gravitational infall and star formation can drive the rms field strength toward equipartition with the mean gas kinetic energy; this field has a generic tendency to self-organize into large coherent structures. If the poloidal component of the field (relative to the rotational axis of a star-forming disc) becomes organized on scales ≲r and attains an energy of order a few per cent of the turbulent energy in the disc, then dynamo effects are expected to generate magnetic torques capable of increasing the inflow speed and thickening the disc. The accretion flow can transport matter towards the centre of mass at a rate adequate to create and grow a massive direct-collapse black hole seed and fuel the subsequent AGN at a high rate, without becoming gravitationally unstable. Fragmentation and star formation are thus suppressed and do not necessarily deplete the mass supply for the accretion flow, in contrast to prevailing models for growing and fuelling SMBHs through disc accretion.

Magnetic Braking during Direct Collapse Black Hole Formation

Magnetic fields are expected to be efficiently amplified during the formation of the first massive black holes via the small-scale dynamo and in the presence of strong accretion shocks occurring during gravitational collapse. Here, we analyze high-resolution cosmological magnetohydrodynamical simulations of gravitational collapse in atomic cooling halos, exploring the dynamical role of magnetic fields, particularly concerning the effect of magnetic braking and angular momentum transport. We find that after the initial amplification, magnetic fields contribute to the transport of angular momentum and reduce it compared to pure hydrodynamical simulations. However, the magnetic and Reynolds torques do not fully compensate for the inward advection of angular momentum, which still accumulates over timescales of ∼1 Myr. A Jeans analysis further shows that magnetic pressure strongly contributes to suppressing fragmentation on scales of 0.1–10 pc. Overall, the presence of magnetic fields thus aids in the transport of angular momentum and favors the formation of massive objects.

Global instability by runaway collisions in nuclear stellar clusters: numerical tests of a route for massive black hole formation

ABSTRACT The centres of galaxies host nuclear stellar clusters, supermassive black holes, or both. The origin of this dichotomy is still a mystery. Nuclear stellar clusters are the densest stellar system in the Universe, so they are ideal places for runaway collisions to occur. Previous studies have proposed the possible existence of a critical mass scale in such clusters, for which the occurrence of collisions becomes very frequent and leads to the formation of a very massive object. While it is difficult to directly probe this scenario with simulations, we here aim for a proof of concept using toy models where the occurrence of such a transition is shown based on simplified compact systems, where the typical evolution time-scales will be faster compared to the real Universe. Indeed our simulations confirm that such a transition takes place and that up to 50 per cent of the cluster mass can go into the formation of a central massive object for clusters that are above the critical mass scale. Our results thus support the proposed new scenario on the basis of idealized simulations. A preliminary analysis of observed nuclear star clusters shows similar trends related to the critical mass as in our simulations. We further discuss the caveats for the application of the proposed scenario in real nuclear star clusters.

Black hole binaries with natal kicks

AbstractWe study the viability of obtaining large natal kicks during the formation of massive black holes (BHs) by studying the asymmetric mild explosion of 21 M⊙ pre‐supernova stellar models, by means of 3D Smooth Particle Hydrodynamics (SPH) simulations. Our preliminary results show either smaller or higher values for the final velocity of the BH than the reduced velocity expected from BH mass accretion, depending on the energy of the explosion.

The X–shooter/ALMA Sample of Quasars in the Epoch of Reionization. II. Black Hole Masses, Eddington Ratios, and the Formation of the First Quasars

We present measurements of black hole masses and Eddington ratios (λ Edd) for a sample of 38 bright (M 1450 < −24.4 mag) quasars at 5.8 ≲ z ≲ 7.5, derived from Very Large Telescope/X–shooter near–IR spectroscopy of their broad C iv and Mg ii emission lines. The black hole masses (on average, M BH ∼ 4.6 × 109 M ⊙) and accretion rates (0.1 ≲ λ Edd ≲ 1.0) are broadly consistent with that of similarly luminous 0.3 ≲ z ≲ 2.3 quasars, but there is evidence for a mild increase in the Eddington ratio above z ≳ 6. Combined with deep Atacama Large Millimeter/submillimeter Array (ALMA) observations of the [C II] 158 μm line from the host galaxies and VLT/MUSE investigations of the extended Lyα halos, this study provides fundamental clues to models of the formation and growth of the first massive galaxies and black holes. Compared to local scaling relations, z ≳ 5.7 black holes appear to be over-massive relative to their hosts, with accretion properties that do not change with host galaxy morphologies. Assuming that the kinematics of the T ∼ 104 K gas, traced by the extended Lyα halos, are dominated by the gravitational potential of the dark matter halo, we observe a similar relation between black hole mass and circular velocity as reported for z ∼ 0 galaxies. These results paint a picture where the first supermassive black holes reside in massive halos at z ≳ 6 and lead the first stages of galaxy formation by rapidly growing in mass with a duty cycle of order unity. The duty cycle needs to drastically drop toward lower redshifts, while the host galaxies continue forming stars at a rate of hundreds of solar masses per year, sustained by the large reservoirs of cool gas surrounding them.

Observational signatures of massive black hole progenitor pathways: could Leo I be a smoking gun?

ABSTRACT Observational evidence is mounting regarding the population demographics of massive black holes (MBHs), from the most massive cluster galaxies down to the dwarf galaxy regime. However, the progenitor pathways from which these central MBHs formed remain unclear. Here, we report a potentially powerful observational signature of MBH formation in dwarf galaxies. We argue that a continuum in the mass spectrum of MBHs in (fossil) dwarf galaxies would be a unique signature of a heavy seed formation pathway. The continuum in this case would consist of the usual population of stellar mass black holes, formed through stellar evolution, plus a smaller population of heavy seed MBHs that have not yet sunk to the centre of the galaxy. Under the robust assumption of initial fragmentation of the parent gas cloud resulting in a burst of heavy seed production, a significant fraction of these seeds will survive to the present day as off-nuclear MBHs with masses less than that of the central object. Motivated by the recent discovery of an MBH in the relatively low central density Leo I galaxy, we show that such a continuum in MBH seed masses should persist from the lightest black hole masses up to the mass of the central MBH in contrast to the light seeding scenario where no such continuum should exist. The detection of off-centred MBHs and a central MBH would represent strong evidence of a heavy seeding pathway.

The Effect of Metallicity on the Formation of Massive Black Holes through Stellar Collisions in Young Massive Star Clusters

Dynamical interactions facilitated by the high densities in massive star clusters can lead to large numbers of stellar collisions and unique stellar evolution pathways not possible for stars evolving in isolation. Using N-body cluster models, we study the role of stellar collisions in the formation of massive black holes, specifically studying the effect of stellar metallicity on this process. We show that at high metallicity (up to solar), the number of massive black holes formed may be reduced by up to a factor of ten compared to low-metallicity clusters. We also examine the role of collisions in the production of pair-instability supernovae and predict event rates of these transients in the local universe.

Massive Black Hole Formation in Dense Stellar Environments: Enhanced X-Ray Detection Rates in High-velocity Dispersion Nuclear Star Clusters

We analyze Chandra X-ray Observatory imaging of 108 galaxies hosting nuclear star clusters (NSCs) to search for signatures of massive black holes (BHs). NSCs are extremely dense stellar environments with conditions that can theoretically facilitate massive BH formation. Recent work by Stone et al. finds that sufficiently dense NSCs should be unstable to the runaway growth of a stellar-mass BH into a massive BH via tidal captures. Furthermore, there is a velocity dispersion threshold (40 km s−1) above which NSCs should inevitably form a massive BH. To provide an observational test of these theories, we measure X-ray emission from NSCs and compare it to the measured velocity dispersion and tidal capture runaway timescale. We find that NSCs above the 40 km s−1 threshold are X-ray detected at roughly twice the rate of those below (after accounting for contamination from X-ray binaries). These results are consistent with a scenario in which dense, high-velocity NSCs can form massive BHs, providing a formation pathway that does not rely on conditions found only at high redshift.

Black hole mergers in compact star clusters and massive black hole formation beyond the mass gap

ABSTRACT We present direct N-body simulations, carried out with nbody6+ + gpu, of young and compact low-metallicity (Z = 0.0002) star clusters with 1.1 × 105 stars, a velocity dispersion of ∼15 $\mathrm{km\, s^{-1}}$, a half-mass radius Rh = 0.6 pc, and a binary fraction of $10{{\ \rm per\,cent}}$ including updated evolution models for stellar winds and (pulsation) pair-instability supernovae (PSNe). Within the first tens of megayears, each cluster hosts several black hole (BH) merger events which nearly cover the complete mass range of primary and secondary BH masses for current LIGO-Virgo-KAGRA gravitational wave detections. The importance of gravitational recoil is estimated statistically during post-processing analysis. We present possible formation paths of massive BHs above the assumed lower PSN mass-gap limit ($45\, {\rm M}_\odot$) into the intermediate-mass black hole (IMBH) regime ($\gt 100\, {\rm M}_\odot$) which include collisions of stars, BHs, and the direct collapse of stellar merger remnants with low core masses. The stellar evolution updates result in the early formation of heavier stellar BHs compared to the previous model. The resulting higher collision rates with massive stars support the rapid formation of massive BHs. For models assuming a high accretion efficiency for star–BH mergers, we present a first-generation formation scenario for GW190521-like events: a merger of two BHs which reached the PSN mass-gap merging with massive stars. This event is independent of gravitational recoil and therefore conceivable in dense stellar systems with low escape velocities. One simulated cluster even forms an IMBH binary (153, 173 M⊙) which is expected to merge within a Hubble time.

Discriminating between different scenarios for the formation and evolution of massive black holes with LISA

Electromagnetic observations have provided strong evidence for the existence of massive black holes in the center of galaxies, but their origin is still poorly known. Different scenarios for the formation and evolution of massive black holes lead to different predictions for their properties and merger rates. LISA observations of coalescing massive black hole binaries could be used to reverse engineer the problem and shed light on these mechanisms. In this paper, we introduce a pipeline based on hierarchical Bayesian inference to infer the mixing fraction between different theoretical models by comparing them to LISA observations of massive black hole mergers. By testing this pipeline against simulated LISA data, we show that it allows us to accurately infer the properties of the massive black hole population as long as our theoretical models provide a reliable description of the Universe. We also show that measurement errors, including both instrumental noise and weak lensing errors, have little impact on the inference.

Growth of massive black hole seeds by migration of stellar and primordial black holes: gravitational waves and stochastic background

We investigate the formation and growth of massive black hole (BH) seeds in dusty star-forming galaxies, relying and extending the framework proposed by [1]. Specifically, the latter envisages the migration of stellar compact remnants (neutron stars and stellar-mass black holes) via gaseous dynamical friction towards the galaxy nuclear region, and their subsequent merging to grow a massive central BH seed. In this paper we add two relevant ingredients: (i) we include primordial BHs, that could constitute a fraction f pBH of the dark matter, as an additional component participating in the seed growth; (ii) we predict the stochastic gravitational wave background originated during the seed growth, both from stellar compact remnant and from primordial BH mergers. We find that the latter events contribute most to the initial growth of the central seed during a timescale of 106–107 yr, before stellar compact remnant mergers and gas accretion take over. In addition, if the fraction of primordial BHs f pBH is large enough, gravitational waves emitted by their mergers in the nuclear galactic regions could be detected by future interferometers like Einsten Telescope, DECIGO and LISA. As for the associated stochastic gravitational wave background, we predict that it extends over the wide frequency band 10-6 ≲ f[Hz] ≲ 10, which is very different from the typical range originated by mergers of isolated binary compact objects. On the one hand, the detection of such a background could be a smoking gun to test the proposed seed growth mechanism; on the other hand, it constitutes a relevant contaminant from astrophysical sources to be characterized and subtracted, in the challenging search for a primordial background of cosmological origin.

Black Hole Science With the Laser Interferometer Space Antenna

The author reviews the scientific potential of the Laser Interferometer Space Antenna (LISA), a space-borne gravitational wave (GW) observatory to be launched in the early 30s. Thanks to its sensitivity in the milli-Hz frequency range, LISA will reveal a variety of GW sources across the Universe, from our Solar neighborhood potentially all the way back to the Big Bang, promising to be a game changer in our understanding of astrophysics, cosmology, and fundamental physics. This review dives in the LISA Universe, with a specific focus on black hole science, including the formation and evolution of massive black holes in galaxy centers, the dynamics of dense nuclei and formation of extreme mass ratio inspirals, and the astrophysics of stellar-origin black hole binaries.

Growth of Stellar-mass Black Holes in Dense Molecular Clouds and GW190521

Abstract A stellar-mass black hole can grow its mass noticeably through Bondi accretion, if it is embedded in an extremely dense and massive molecular cloud with slow motion with respect to the ambient medium for an extended period of time. This provides a novel, yet challenging channel for the formation of massive stellar-mass black holes. We discuss how this channel may account for the massive binary black hole merger system GW190521 as observed by LIGO/Virgo gravitational wave detectors as well as the claimed massive black hole candidate LB-1.

Observational Support for Massive Black Hole Formation Driven by Runaway Stellar Collisions in Galactic Nuclei

Abstract We explore a scenario for massive black hole formation driven by stellar collisions in galactic nuclei, proposing a new formation regime of global instability in nuclear stellar clusters triggered by runaway stellar collisions. Using order-of-magnitude estimations, we show that observed nuclear stellar clusters avoid the regime where stellar collisions are dynamically relevant over the whole system, while resolved detections of massive black holes are well into such collision-dominated regimes. We interpret this result in terms of massive black holes and nuclear stellar clusters being different evolutionary paths of a common formation mechanism, unified under the standard terminology of both being central massive objects. We propose a formation scenario where central massive objects more massive than ∼108 M ⊙, which also have relaxation times longer that their collision times, will be too dense (in virial equilibrium) to be globally stable against stellar collisions, and most of the mass will collapse toward the formation of a massive black hole. Contrarily, this will only be the case at the core of less dense central massive objects, leading to the formation of black holes with much lower black hole efficiencies , with these efficiencies ϵ BH drastically growing for central massive objects more massive than ∼107 M ⊙, approaching unity around M CMO ∼ 108 M ⊙. We show that the proposed scenario successfully explains the relative trends observed in the masses, efficiencies, and scaling relations between massive black holes and nuclear stellar clusters.

A new channel to form IMBHs throughout cosmic time

ABSTRACT While the formation of the first black holes (BHs) at high redshift is reasonably well understood though debated, massive BH formation at later cosmic epochs has not been adequately explored. We present a gas accretion driven mechanism that can build-up BH masses rapidly in dense, gas-rich nuclear star clusters (NSCs). Wind-fed supraexponential accretion in these environments under the assumption of net zero angular momentum for the gas, can lead to extremely rapid growth, scaling stellar mass remnant seed BHs up to the intermediate mass black hole (IMBH) range. This new long-lived channel for IMBH formation permits growth to final masses ranging from 50 to 105 M⊙. Growth is modulated by the gas supply, and premature termination can result in the formation of BHs with masses between 50 and a few 100 M⊙ filling in the so-called mass gap. Typically, growth is unimpeded and will result in the formation of IMBHs with masses ranging from ∼100 to 105 M⊙. New detections from the LIGO–VIRGO source GW190521 to the emerging population of ∼105 M⊙ BHs harboured in low-mass dwarf galaxies are revealing this elusive population. Naturally accounting for the presence of off-centre BHs in low-mass dwarfs, this new pathway also predicts the existence of a population of wandering non-central BHs in more massive galaxies detectable via tidal disruption events and as gravitational wave coalescences. Gas-rich NSCs could therefore serve as incubators for the continual formation of BHs over a wide range in mass throughout cosmic time.

General-relativistic instability in hylotropic supermassive stars

Context. The formation of supermassive black holes by direct collapse would imply the existence of supermassive stars (SMSs) and their collapse through the general-relativistic (GR) instability into massive black hole seeds. However, the final mass of SMSs is weakly constrained by existing models, in spite of the importance of this value for the consistency of the direct collapse scenario. Aims. We estimate the final masses of spherical SMSs within the whole parameter space that is relevant to these objects. Methods. We built analytical stellar structures (hylotropes) that mimic existing numerical SMS models, accounting for full stellar evolution with rapid accretion. From these hydrostatic structures, we determine ab initio the conditions for GR instability and compare the results with the predictions for full stellar evolution. Results. We show that hylotropic models predict the onset of GR instability with a high level of precision. The mass of the convective core appears as a decisive quantity. The lower it is, the larger the total mass required for GR instability. The typical conditions for GR instability feature a total mass of ≳105 M⊙ with a core mass of ≳104 M⊙. If the core mass remains below 104 M⊙, total masses in excess of 106 − 107 M⊙ can be reached. Conclusions. Our results confirm that spherical SMSs forming in primordial, atomically cooled haloes collapse at masses below 500 000 M⊙. On the other hand, accretion rates in excess of 1000 M⊙ yr−1, leading to final stellar masses of ≳106 M⊙, are required for massive black hole formation in metal-rich gas. Thus, the different channels of direct collapse imply distinct final masses for the progenitor of the black hole seed.