Toward Black Hole Stars: Supermassive Black Hole Growth in Nuclear Clusters via Stellar-object and Gas Accretion

Tidal disruption events (TDEs) are a class of transients that occur when a star is destroyed by the tides of a massive black hole (MBH). Their rates encode valuable MBH demographic information, but this can only be extracted if accurate TDE rate predictions are available for comparisons with observed rates. In this work, we present a new, observer-friendly Python package called REPTiDE, which implements a standard loss-cone model for computing TDE rates given a stellar density distribution and an MBH mass. We apply this software to a representative sample of 91 nearby galaxies over a wide range of stellar masses with high-resolution nuclear density measurements from C. H. Hannah et al. We measure per-galaxy TDE rates ranging between 10−7.7 and 10−2.9 yr–1 and find that the sample-averaged rates agree well with observations. We find a turnover in the TDE rate as a function of both galaxy stellar mass and black hole mass, with the peak rates being observed in galaxies at a galaxy mass of 109.5 M ⊙ and a black hole mass of 106.5 M ⊙. Despite the lower TDE rates inferred for intermediate-mass black holes, we find that they have gained a higher fraction of their mass through TDEs when compared to higher-mass black holes. This growth of lower-mass black holes through TDEs can enable us to place interesting constraints on their spins; we find maximum spins of a • ≈ 0.9 for black holes with masses below ∼105.5 M ⊙.

Previous studies suggest that the growth of supermassive black holes (SMBHs) may be fundamentally related to host-galaxy stellar mass (M ). To investigate this SMBH growth-M relation in detail, we calculate long-term SMBH accretion rate as a function of M and redshift [BHAR(M , z)] over ranges of log (M /M ) = 9.5-12 and z = 0.4-4. Our BHAR(M , z) is constrained by high-quality survey data (GOODS-South, GOODS-North and COSMOS), and by the stellar mass function and the X-ray luminosity function. At a given M , BHAR is higher at high redshift. This redshift dependence is stronger in more massive systems [for log (M /M ) 11.5, BHAR is three decades higher at z = 4 than at z = 0.5], possibly due to AGN feedback. Our results indicate that the ratio between BHAR and average star formation rate (SFR) rises towards high M at a given redshift. This BHAR/SFR dependence on M does not support the scenario that SMBH and galaxy growth are in lockstep. We calculate SMBH mass history [M BH (z)] based on our BHAR(M , z) and the M (z) from the literature, and find that the M BH -M relation has weak redshift evolution since z 2. The M BH /M ratio is higher towards massive galaxies: it rises from 1/5000 at log M 10.5 to 1/500 at log M 11.2. Our predicted M BH /M ratio at high M is similar to that observed in local giant ellipticals, suggesting that SMBH growth from mergers is unlikely to dominate over growth from accretion.

ABSTRACTWe present N-body simulations, including post-Newtonian dynamics, of dense clusters of low-mass stars harbouring central black holes (BHs) with initial masses of 50, 300, and 2000 M⊙. The models are evolved with the N-body code bifrost to investigate the possible formation and growth of massive BHs by the tidal capture of stars and tidal disruption events (TDEs). We model star–BH tidal interactions using a velocity-dependent drag force, which causes orbital energy and angular momentum loss near the BH. About ∼20–30 per cent of the stars within the spheres of influence of the black holes form Bahcall–Wolf cusps and prevent the systems from core collapse. Within the first 40 Myr of evolution, the systems experience 500–1300 TDEs, depending on the initial cluster structure. Most (>95 per cent) of the TDEs originate from stars in the Bahcall–Wolf cusp. We derive an analytical formula for the TDE rate as a function of the central BH mass, density, and velocity dispersion of the clusters ($\dot{N}_{\mathrm{TDE}} \propto M\mathrm{_{BH}}\rho \sigma ^{-3}$). We find that TDEs can lead a 300 M⊙ BH to reach $\sim 7000 \, \mathrm{{M}_{\odot }}$ within a Gyr. This indicates that TDEs can drive the formation and growth of massive BHs in sufficiently dense environments, which might be present in the central regions of nuclear star clusters.

To date, most of the luminous quasars known at z ∼ 6 have been found to be in maximal accretion with the Eddington ratios, , suggesting enhanced nuclear activities in the early universe. However, this may not be the whole picture of supermassive black hole (SMBH) growth, since previous studies have not reached faint quasars that are more likely to harbor SMBHs with low . To gain a better understanding of the accretion activities in quasars in the early universe, we obtained a deep near-infrared (NIR) spectrum of a quasar, IMS J220417.92+011144.8 (hereafter IMS J2204+0112), one of the faintest quasars that has been identified at z ∼ 6. From the redshifted C iv λ1549 emission line in the NIR spectrum, we find that IMS J2204+0112 harbors a SMBH with a solar mass of about a billion and , but with a large uncertainty in both quantities (0.41 dex). IMS J2204+0112 has one of the lowest Eddington ratios among quasars at z ∼ 6, but a common value among quasars at z ∼ 2. Its low can be explained with two scenarios; the SMBH growth from a stellar-mass black hole through short-duration super-Eddington accretion events or from a massive black hole seed ( ) with Eddington-limited accretion. NIR spectra of more faint quasars are needed to better understand the accretion activities of SMBHs at z ∼ 6.

We present a comprehensive synthesis model for the active galactic nuclei (AGN) evolution and the growth of supermassive black hole (SMBH) in the Universe. We assume that black holes accrete in just three distinct physical states, or 'modes': at low Eddington ratio, only a radiatively inefficient, kinetically dominated mode is allowed [low kinetic (LK)]; at high Eddington ratio, instead, AGN may display both a purely radiative [radio quiet, high radiative (HR)] and a kinetic [radio loud, high kinetic (HK)] mode. We solve the continuity equation for the black hole mass function using the locally determined one as a boundary condition, and the hard X-ray luminosity function as tracer of the AGN growth rate distribution, supplemented with a luminosity-dependent bolometric correction and an absorbing column distribution. Differently from most previous semi-analytic and numerical models for black hole growth, we do not assume any specific distribution of Eddington ratios, rather we determine it empirically by coupling the mass and luminosity functions and a set of fundamental relations between observables in the three accretion modes. SMBH always show a very broad accretion rate distribution, and we discuss the profound consequences of this fact for our understanding of observed AGN fractions in galaxies, as well as for the empirical determination of SMBH mass functions with large surveys. We confirm previous results and clearly demonstrate that, at least for z≤ 1.5, SMBH mass function evolves antihierarchically, i.e. the most massive holes grew earlier and faster than less massive ones. For the first time, we find hints of a reversal of such a downsizing behaviour at redshifts above the peak of the black hole accretion rate density (z ≈2). We also derive tight constraints on the (mass-weighted) average radiative efficiency of AGN: under the simplifying assumption that the mass density of both high redshift (z ∼5) and 'wandering' black holes ejected from galactic nuclei after merger events are negligible compared to the local mass density, we find that 0.065 0.07, where ξ 0 is the local SMBH mass density in units of 4.3 x 10 5 M ⊙ Mpc -3 . We trace the cosmological evolution of the kinetic luminosity function of AGN, and find that the overall efficiency of SMBH in converting accreted rest mass energy into kinetic power, e kin , ranges between e kin ≃ (3-5) x 10 -3 , depending on the choice of the radio core luminosity function. Such a 'kinetic efficiency' varies however strongly with SMBH mass and redshift, being maximal for very massive holes at late times, as required for the AGN feedback by many galaxy formation models in cosmological contexts.

Context. The large-scale environments of active galactic nuclei (AGNs) reveal important information on the growth and evolution of supermassive black holes (SMBHs). Previous AGN clustering measurements using two-point correlation functions have hinted that AGNs with massive black holes preferentially reside in denser cosmic regions than AGNs with less massive SMBHs. At the same time, little to no dependence on the accretion rate has been found; however, the significance of such trends has been limited. Aims. Here, we present k th-nearest-neighbor ( k NN) statistics of 2MASS galaxies around AGNs from the Swift/BAT AGN Spectroscopic survey. These statistics have been shown to contribute additional higher order clustering information on the cosmic density field. Methods. By calculating the distances to the nearest seven galaxy neighbors in angular separation to each AGN within two redshift ranges (0.01 < z < 0.03 and 0.03 < z < 0.06), we compared their cumulative distribution functions to that of a randomly distributed sample to demonstrate the sensitivity of this method to the clustering of AGNs. We also split the AGNs into bins of bolometric luminosity, black hole mass, and Eddington ratio (while controlling for redshift) to search for trends between k NN statistics and fundamental AGN properties. Results. We find that AGNs with massive SMBHs have significantly closer neighbors than AGNs with less massive SMBHs (at the 99.98% confidence level), especially in our lower redshift range. We find less significant trends with luminosity or Eddington ratio. By comparing our results to empirical SMBH-galaxy-halo models implemented in N-body simulations, we show that small-scale k NN trends with black hole mass may go beyond stellar mass dependencies. Conclusions. This suggests that massive SMBHs in the local universe reside in more massive dark matter halos and denser regions of the cosmic web, which may indicate that environment is important for the growth of SMBHs, bolstering prior conclusions based on correlation functions.

Aims. It is speculated that a merger of two massive stellar-origin black holes in a dense stellar environment may lead to the formation of a massive black hole in the pair-instability mass gap (∼50−135 M⊙). Such a merger-formed black hole is expected to typically have a high spin (a ∼ 0.7). If such a massive black hole acquires another black hole it may lead to another merger detectable by LIGO/Virgo in gravitational waves. Acquiring a companion may be hindered by gravitational-wave kick/recoil, which accompanies the first merger and may quickly remove the massive black hole from its parent globular or nuclear cluster. We test whether it is possible for a massive merger-formed black hole in the pair-instability gap to be retained in its parent cluster and have low spin. Such a black hole would be indistinguishable from a primordial black hole. Methods. We employed results from numerical relativity calculations of black hole mergers to explore the range of gravitational-wave recoil velocities for various combinations of merging black hole masses and spins. We compared merger-formed massive black hole speeds with typical escape velocities from globular and nuclear clusters. Results. We show that a globular cluster is highly unlikely to form and retain a ∼100 M⊙ black hole if the spin of the black hole is low (a ≲ 0.3). Massive merger-formed black holes with low spins acquire high recoil speeds (≳ 200 km s−1) from gravitational-wave kick during formation that exceed typical escape speeds from globular clusters (∼ 50 km s−1). However, a very low-spinning (a ∼ 0.1) and massive (∼100 M⊙) black hole could be formed and retained in a galactic nuclear star cluster. Even though such massive merger-formed black holes with such low spins acquire high speeds during formation (∼ 400 km s−1), they may avoid ejection since massive nuclear clusters have high escape velocities (∼ 300−500 km s−1). A future detection of a massive black hole in the pair-instability mass gap with low spin would therefore not be proof of the existence of primordial black holes, which are sometimes claimed to have low spins and arbitrarily high masses.

We suggest a new picture of supermassive black hole (SMBH) growth in galaxy centers. Momentum-driven feedback from an accreting hole gives significant orbital energy but little angular momentum to the surrounding gas. Once central accretion drops, the feedback weakens and swept-up gas falls back towards the SMBH on near-parabolic orbits. These intersect near the black hole with partially opposed specific angular momenta, causing further infall and ultimately the formation of a small-scale accretion disk. The feeding rates into the disk typically exceed Eddington by factors of a few, growing the hole on the Salpeter timescale and stimulating further feedback. Natural consequences of this picture include (i) the formation and maintenance of a roughly toroidal distribution of obscuring matter near the hole; (ii) random orientations of successive accretion disk episodes; (iii) the possibility of rapid SMBH growth; (iv) tidal disruption of stars and close binaries formed from infalling gas, resulting in visible flares and ejection of hypervelocity stars; (v) super-solar abundances of the matter accreting on to the SMBH; and (vi) a lower central dark-matter density, and hence annihilation signal, than adiabatic SMBH growth implies. We also suggest a simple sub-grid recipe for implementing this process in numerical simulations.

The volumetric rate of tidal disruption events (TDEs) encodes information on the still-unknown demographics of central massive black holes (MBHs) in low-mass galaxies (≲109 M ⊙). Theoretical TDE rates from model galaxy samples can extract this information, but this requires accurately defining the nuclear stellar density structures. This region is typically dominated by nuclear star clusters (NSCs), which have been shown to increase TDE rates by orders of magnitude. Thus, we assemble the largest available sample of parsec-scale 3D density profiles that include NSC components. We deproject the point-spread-function-deconvolved surface-brightness profiles of 91 nearby galaxies of varying morphology and combine these with nuclear mass-to-light ratios estimated from measured colors or spectral synthesis to create 3D mass density profiles. We fit the inner 3D density profile to find the best-fit power-law density profile in each galaxy. We compile this information as a function of galaxy stellar mass to fit new empirical density scaling relations. These fits reveal positive correlations between galaxy stellar mass and central stellar density in both early- and late-type galaxies. We find that early-type galaxies have somewhat higher densities and shallower profiles relative to late-type galaxies at the same mass. We also use the density profiles to estimate the influence radius of each galaxy’s MBH and find that the sphere of influence was likely resolved in most cases. These new relations will be used in future works to build mock galaxy samples for dynamical TDE rate calculations, with the aim of constraining MBH demographics in low-mass galaxies.

It is assumed that a galaxy starts as a dark halo of a few million Jeans clusters (JCs), each of which consists of nearly a trillion micro brown dwarfs, MACHOs of Earth mass. JCs in the galaxy center heat up their MACHOs by tidal forces, which makes them expand, so that coagulation and star formation occurs. Being continuously fed by matter from bypassing JCs, the central star(s) may transform into a super massive black hole. It has a fast t3 growth during the first mega years, and a slow t1/3 growth at giga years. JCs disrupted by a close encounter with this black hole can provide matter for the bulge. Those that survive can be so agitated that they form stars inside them and become globular star clusters. Thus black holes mostly arise together with galactic bulges in their own environment and are about as old as the oldest globular clusters. The age 13.2 Gy of the star HE 1523-0901 puts forward that the Galactic halo was fully assembled at that moment. The star formation rate has a maximum at black hole mass ∼4·107M⊙ and bulge mass ∼5·1010M⊙. In case of merging supermassive black holes the JCs passing near the galactic center provide ideal assistance to overcome the last parsec.

Recent observations and simulations have challenged the long-held paradigm that mergers are the dominant mechanism driving the growth of both galaxies and supermassive black holes (SMBH), in favour of non-merger (secular) processes. In this pilot study of merger-free SMBH and galaxy growth, we use Keck Cosmic Web Imager spectral observations to examine four low-redshift (0.043 < z < 0.073) disc-dominated ‘bulgeless’ galaxies hosting luminous active galactic nucleus (AGN), assumed to be merger-free. We detect blueshifted broadened [O iii] emission from outflows in all four sources, which the $\mathrm{[O\, \small {III}]}$/$\rm {H}\beta$ ratios reveal are ionized by the AGN. We calculate outflow rates in the range $0.12{-}0.7~\rm {M}_{\odot }~\rm {yr}^{-1}$, with velocities of $675{-}1710~\rm {km}~\rm {s}^{-1}$, large radial extents of $0.6{-}2.4~\rm {kpc}$, and SMBH accretion rates of $0.02{-}0.07~\rm {M}_{\odot }~\rm {yr}^{-1}$. We find that the outflow rates, kinematics, and energy injection rates are typical of the wider population of low-redshift AGN, and have velocities exceeding the galaxy escape velocity by a factor of ∼30, suggesting that these outflows will have a substantial impact through AGN feedback. Therefore, if both merger-driven and non-merger-driven SMBH growth lead to co-evolution, this suggests that co-evolution is regulated by feedback in both scenarios. Simulations find that bars and spiral arms can drive inflows to galactic centers at rates an order of magnitude larger than the combined SMBH accretion and outflow rates of our four targets. This work therefore provides further evidence that non-merger processes are sufficient to fuel SMBH growth and AGN outflows in disc galaxies.

Stars passing too close to a super massive black hole (SMBH) can produce tidal disruption events (TDEs). Since the resulting stellar debris can produce an electromagnetic flare, TDEs are believed to probe the presence of single SMBHs in galactic nuclei, which otherwise remain dark. In this paper, we show how stars orbiting an IMBH secondary are perturbed by an SMBH primary. We find that the evolution of the stellar orbits are severely affected by the primary SMBH due to secular effects and stars orbiting with high inclinations with respect to the SMBH-IMBH orbital plane end their lives as TDEs due to Kozai-Lidov oscillations, hence illuminating the secondary SMBH/IMBH. Above a critical SMBH mass of $\approx 1.15 \times 10^8$ M$_{\odot}$, no TDE can occur for typical stars in an old stellar population since the Schwarzschild radius exceeds the tidal disruption radius. Consequently, any TDEs due to such massive SMBHs will remain dark. It follows that no TDEs should be observed in galaxies with bulges more massive than $\approx 4.15\times 10^{10}$ M$_{\odot}$, unless a lower-mass secondary SMBH or IMBH is also present. The secular mechanism for producing TDEs considered here therefore offers a useful probe of SMBH-SMBH/IMBH binarity in the most massive galaxies. We further show that the TDE rate can be $\approx 10^{-4}-10^{-3}$ yr$^{-1}$, and that most TDEs occur on $\approx 0.5$ Myr. Finally, we show that stars may be ejected with velocities up to thousands of km s$^{-1}$, which could contribute to the observed population of Galactic hypervelocity stars.

In this work, we use the constrained Gaussian realization technique to study the early growth of supermassive black holes (SMBHs) in cosmological hydrodynamic simulations, exploring its relationship with features of the initial density peaks on large scales, ∼ 1 h−1Mpc. Our constrained simulations of volume (20 h−1Mpc)3 successfully reconstruct the large-scale structure as well as the black hole growth for the hosts of the rare 109 M⊙ SMBHs found in the bluetides simulation at z ∼ 7. We run a set of simulations with constrained initial conditions by imposing a $5 \sigma _0(R_\mathrm{G})$ peak on the scale of $\\ R_\mathrm{ G} = 1$ h−1Mpc varying different peak features, such as the shape and compactness as well as the tidal field surrounding the peak. We find that initial density peaks with high compactness and low tidal field induce the most rapid BH growth at early epochs. This is because compact density peaks with a more spherical large-scale matter distribution lead to the formation of the highest gas inflows (mostly radial) in the centres of haloes which boost the early BH accretion. Moreover, such initially compact density peaks in low tidal field regions also lead to a more compact BH host galaxy morphology. Our findings can help explain the tight correlation between BH growth and host galaxy compactness seen in observations.

Presence of supermassive black holes (SMBHs) with mass (106 − 109) M⊙ at z = 10 has been recently revealed by James Webb Space Telescope (JWST) observations. In this study we generate seeds for the above range of SMBHs in various background cosmologies. We consider cosmic timescales required for black hole growth provided by three general relativistic cosmological models (ΛCDM, ωCDM and Dynamical Dark Energy(DDE) and the braneworld cosmology. The growth of SMBHs is studied through Eddington limited and super-Eddington accretion, where the accretion starts at z=30. It is found that growth of SMBHs by z=10 within Eddington limited accretion is possible through massive seeds (M ≥ 104 M⊙) in all cosmologies. Super Eddington accretion onto spinning black holes with mass of few tens of solar masses can result in SMBHs by z=10 in all cosmologies. The viable cosmologies considered here are found to be unable to strongly distinguish between the seed black hole masses. The seeds generated in this work are assumed to be of primordial origin in order to satisfy the criteria of formation of high redshift massive galaxies. The fraction of primordial black holes (PBHs) contributing to dark matter (fPBH) and their corresponding number densities for the mass range (105–108) M⊙ are calculated in both seed effect and Poisson effect. In seed effect, PBHs of mass ≥107 M⊙ contributes ≤10−2 to the dark matter fraction. The evolution of gas mass inside a PBH seeded dark matter halo is studied. The ratio of black hole to stellar mass is also evaluated for star formation efficiency in the range (0.1-1) and found to be (10−3 − 1) for MBH = 108 M⊙ and (10−2 − 10) for MBH = 109 M⊙.

We quantify the importance of mass accretion during AGN phases in the growth of supermassive black holes (BH) by comparing the mass function of black holes in the local universe with that expected from AGN relics, which are black holes grown entirely with mass accretion during AGN phases. The local BH mass function (BHMF) is estimated by applying the well-known correlations between BH mass, bulge luminosity and stellar velocity dispersion to galaxy luminosity and velocity functions. The density of BHs in the local universe is .To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html