Local Black Hole Research Articles

Scalar field propagation in braneworld black hole scenario obtained from Nash theorem

We determine the scalar field evolution of a braneworld localized black hole with both dark matter and dark energy components, obtained within a dynamical and continuous embedding formalism by use of Nash’s theorem. We further extract the associated quasinormal modes for both de Sitter–Schwarzschild-Dark matter and anti-de Sitter–Schwarzschild-Dark matter solutions, for the different causal structures (one, two or three horizon spacetimes) given by the space of parameters. By comparison with standard solutions within stand alone general relativity, we conclude with comments on possible observable astrophysical differences via quasinormal spectra, and remark on the interpretations of previous AdS/CFT correspondence scenarios.

Accretion History of AGNs. III. Radiative Efficiency and AGN Contribution to Reionization

Abstract The cosmic history of supermassive black hole (SMBH) growth is important for understanding galaxy evolution, reionization, and the physics of accretion. Recent NuSTAR, Swift-BAT, and Chandra hard X-ray surveys have provided new constraints on the space density of heavily obscured active galactic nuclei (AGNs). Using the new X-ray luminosity function derived from these data, we here estimate the accretion efficiency of SMBHs and their contribution to reionization. We calculate the total ionizing radiation from AGNs as a function of redshift, based on the X radiation and distribution of obscuring column density, converted to ultraviolet (UV) wavelengths. Limiting the luminosity function to unobscured AGNs only, our results agree with current UV luminosity functions of unobscured AGNs. For realistic assumptions about the escape fraction, the contribution of all AGNs to cosmic reionization is ∼4 times lower than the galaxy contribution (23% at z ∼ 6). Our results also offer an observationally constrained prescription that can be used in simulations or models of galaxy evolution. To estimate the average efficiency with which SMBHs convert mass to light, we compare the total radiated energy, converted from X-ray light using a bolometric correction, with the most recent local black hole mass density. The most likely value, η ∼ 0.3–0.34, approaches the theoretical limit for a maximally rotating Kerr black hole, η = 0.42, implying that on average growing SMBHs are spinning rapidly.

Nuclear X-Ray Activity in Low-surface-brightness Galaxies: Prospects for Constraining the Local Black Hole Occupation Fraction with a Chandra Successor Mission

Abstract About half of nearby galaxies have a central surface brightness ≥1 mag below that of the sky. The overall properties of these low-surface-brightness galaxies (LSBGs) remain understudied, and in particular we know very little about their massive black hole population. This gap must be closed to determine the frequency of massive black holes at z = 0 as well as to understand their role in regulating galaxy evolution. Here we investigate the incidence and intensity of nuclear, accretion-powered X-ray emission in a sample of 32 nearby LSBGs with the Chandra X-ray Observatory. A nuclear X-ray source is detected in four galaxies (12.5%). Based on an X-ray binary contamination assessment technique developed for normal galaxies, we conclude that the detected X-ray nuclei indicate low-level accretion from massive black holes. The active fraction is consistent with that expected from the stellar mass distribution of the LSBGs, but not their total baryonic mass, when using a scaling relation from an unbiased X-ray survey of normal galaxies. This suggests that their black holes co-evolved with their stellar population. In addition, the apparent agreement nearly doubles the number of galaxies available within ∼100 Mpc for which a measurement of nuclear activity can efficiently constrain the frequency of black holes as a function of stellar mass. We conclude by discussing the feasibility of measuring this occupation fraction to a few percent precision below ≲1010 M ⊙ with high-resolution, wide-field X-ray missions currently under consideration.

Enhancement of the tidal disruption event rate in galaxies with a nuclear star cluster: from dwarfs to ellipticals

ABSTRACT We compute the tidal disruption event (TDE) rate around local massive black holes (MBHs) with masses as low as $2.5\times 10^4\, \mathrm{M}_{\odot }$, thus probing the dwarf regime for the first time. We select a sample of 37 galaxies for which we have the surface stellar density profile, a dynamical estimate of the mass of the MBH, and 6 of which, including our Milky Way, have a resolved nuclear star cluster (NSC). For the Milky Way, we find a total TDE rate of ${\sim}10^{-4}\, \mathrm{yr}^{-1}$ when taking the NSC in account, and ${\sim}10^{-7} \, \mathrm{yr}^{-1}$ otherwise. TDEs are mainly sourced from the NSC for light (${\lt}3\times 10^{10}\, \mathrm{M}_{\odot }$) galaxies, with a rate of few $10^{-5}\, \mathrm{yr}^{-1}$, and an enhancement of up to two orders of magnitude compared to non-nucleated galaxies. We create a mock population of galaxies using different sets of scaling relations to explore trends with galaxy mass, taking into account the nucleated fraction of galaxies. Overall, we find a rate of few $10^{-5}\, \mathrm{yr}^{-1}$ which drops when galaxies are more massive than $10^{11}\, \mathrm{M}_{\odot }$ and contain MBHs swallowing stars whole and resulting in no observable TDE.

From galactic nuclei to the halo outskirts: tracing supermassive black holes across cosmic history and environments

ABSTRACT We study the mass assembly and spin evolution of supermassive black holes (BHs) across cosmic time as well as the impact of gravitational recoil on the population of nuclear and wandering BHs (wBHs) by using the semi-analytical model L-Galaxies run on top of Millennium merger trees. We track spin changes that BHs experience during both coalescence events and gas accretion phases. For the latter, we assume that spin changes are coupled with the bulge assembly. This assumption leads to predictions for the median spin values of z = 0 BHs that depend on whether they are hosted by pseudo-bulges, classical bulges or ellipticals, being $\overline{a} \sim 0.9$, 0.7 and 0.4, respectively. The outcomes of the model display a good consistency with $z \le 4$ quasar luminosity functions and the $z = 0$ BH mass function, spin values, and BH correlation. Regarding the wBHs, we assume that they can originate from both the disruption of satellite galaxies (orphan wBH) and ejections due to gravitational recoils (ejected wBH). The model points to a number density of wBHs that increases with decreasing redshift, although this population is always $\rm {\sim}2\, dex$ smaller than the one of nuclear BHs. At all redshifts, wBHs are typically hosted in $\rm {\it M}_{halo} \gtrsim 10^{13} \, M_{\odot }$ and $\rm {\it M}_{stellar} \gtrsim 10^{10} \, M_{\odot }$, being orphan wBHs the dominant type. Besides, independently of redshift and halo mass, ejected wBHs inhabit the central regions (${\lesssim}\rm 0.3{\it R}_{200}$) of the host DM halo, while orphan wBH linger at larger scales (${\gtrsim}\rm 0.5{\it R}_{200}$). Finally, we find that gravitational recoils cause a progressive depletion of nuclear BHs with decreasing redshift and stellar mass. Moreover, ejection events lead to changes in the predicted local BH–bulge relation, in particular for BHs in pseudo-bulges, for which the relation is flattened at $\rm {\it M}_{bulge} \gt 10^{10.2}\, M_{\odot }$ and the scatter increase up to ${\sim}\rm 3\, dex$.

Constraining black hole–galaxy scaling relations and radiative efficiency from galaxy clustering

The masses of supermassive black holes are observed to increase with either the total mass or the mean (random) velocity of the stars in their host galaxies. The origin of these correlations remains elusive due to observational systematics and biases that severely limit our knowledge of the local demography of supermassive black holes. Here, we show that the large-scale spatial distribution of local active galactic nuclei (AGN) can constrain the shape and normalization of the black hole–stellar mass relation, thus bypassing resolution-related observational biases. In turn, our results can set more stringent constraints on the AGN radiative efficiency, e. For currently accepted values of the AGN obscured fractions and bolometric corrections, our estimated local supermassive black hole mass density favours mean e values of ~10–20%, suggesting that the vast majority of supermassive black holes are spinning moderately to rapidly. With large-scale AGN surveys coming online, our methodology will enable even tighter constraints on the fundamental parameters that regulate the growth of supermassive black holes. The large-scale spatial distribution of local active galactic nuclei can constrain the black hole–stellar mass relation and their mean radiative efficiency to 10–20%, suggesting moderate to high spins for the vast majority of supermassive black holes.

The fate of instability of de Sitter black holes at large D

We study non-linearly the gravitational instabilities of the Reissner- Nordstrom-de Sitter and the Gauss-Bonnet-de Sitter black holes by using the large D expansion method. In both cases, the thresholds of the instability are found to be con- sistent with the linear analysis, and on the thresholds the evolutions of the black holes under the perturbations settle down to stationary lumpy solutions. However, the solutions in the unstable region are highly time-dependent, and resemble the fully localized black spots and black ring with SD−2 and S1× SD−3 topologies, respectively. Our study indi- cates the possible transition between the lumpy black holes and the localized black holes in higher dimensions.

Exploring the Local Black Hole Mass Function below 106 Solar Masses

Abstract The local black hole mass function (BHMF) is of great interest to a variety of astrophysical problems, ranging from black hole binary merger rates to an indirect census of the dominant seeding mechanism of supermassive black holes. In this Letter, we combine the latest galaxy stellar mass function from the Galaxy And Mass Assembly survey with X-ray-based constraints to the local black hole occupation fraction to probe the BHMF below 106 M ⊙. Notwithstanding the large uncertainties inherent to the choice of a reliable observational proxy for black hole mass, the resulting range of BHMFs yields a combined normalization uncertainty of ≲1 dex over the [105–106] M ⊙ range, where upcoming, space-based gravitational wave detectors are designed to be most sensitive.

The clustering of undetected high-redshift black holes and their signatures in cosmic backgrounds

ABSTRACT There exist hitherto unexplained fluctuations in the cosmic infrared background on arcminute scales and larger. These have been shown to cross-correlate with the cosmic X-ray background, leading several authors to attribute the excess to a high-redshift growing black hole population. In order to investigate potential sources that could explain this excess, in this paper, we develop a new framework to compute the power spectrum of undetected sources that do not have constant flux as a function of halo mass. In this formulation, we combine a semi-analytic model for black hole growth and their simulated spectra from hydrodynamical simulations. Revisiting the possible contribution of a high-redshift black hole population, we find that too much black hole growth is required at early epochs for z > 6 accretion to explain these fluctuations. Examining a population of accreting black holes at more moderate redshifts, z ∼ 2–3, we find that such models produce a poor fit to the observed fluctuations while simultaneously overproducing the local black hole mass density. Additionally, we rule out the hypothesis of a missing Galactic foreground of warm dust that produces coherent fluctuations in the X-ray via reflection of Galactic X-ray binary emission. Although we firmly rule out accreting massive black holes as the source of these missing fluctuations, additional studies will be required to determine their origin.

Stronger Constraints on the Evolution of the MBH− Relation up to z ∼ 0.6

Abstract We revisit the possibility of redshift evolution in the M BH−σ * relation with a sample of 22 Seyfert 1 galaxies with black holes (BHs) in the mass range and redshift range 0.03 < z < 0.57 with spectra obtained from spatially resolved Keck/Low-resolution Imaging Spectrometer observations. Stellar velocity dispersions were measured directly from the Mg ib region, taking into consideration the effect of Fe ii contamination, active galactic nucleus (AGN) dilution, and host-galaxy morphology on our measurements. BH masses are estimated using the Hβ line width, and the luminosity at 5100 Å is estimated from surface brightness decomposition of the AGN from the host galaxy using high-resolution imaging from the Hubble Space Telescope. Additionally, we investigate the use of the [O iii]λ5007 emission line width as a surrogate for stellar velocity dispersion, finding better correlation once corrected for Fe ii contamination and any possible blueshifted wing components. Our selection criteria allowed us to probe lower-luminosity AGNs and lower-mass BHs in the non-local universe than those measured in previous single-epoch studies. We find that any offset in the M BH−σ * relation up to z ∼ 0.6 is consistent with the scatter of local BH masses, and address the sources of biases and uncertainties that contribute to this scatter.

Constraining the stellar mass function from the deficiency of tidal disruption flares in the nuclei of massive galaxies

ABSTRACT The rate of tidal disruption flares (TDFs) per mass of the disrupting black hole encodes information on the present-day mass function (PDMF) of stars in the clusters surrounding super massive black holes. We explore how the shape of the TDF rate with black hole mass can constrain the PDMF, with only weak dependence on black hole spin. We show that existing data can marginally constrain the minimum and maximum masses of stars in the cluster, and the high-mass end of the PDMF slope, as well as the overall TDF rate. With $\mathcal {O}(100)$ TDFs expected to be identified with the Zwicky Transient Facility, the overall rate can be highly constrained, but still with only marginal constraints on the PDMF. However, if ${\lesssim } 10 {{\ \rm per\ cent}}$ of the TDFs expected to be found by LSST over a decade ($\mathcal {O}(10^3)$ TDFs) are identified, then precise and accurate estimates can be made for the minimum stellar mass (within a factor of 2) and the average slope of the high-mass PDMF (to within $\mathcal {O}(10{{\ \rm per\ cent}})$) in nuclear star clusters. This technique could be adapted in the future to probe, in addition to the PDMF, the local black hole mass function and possibly the massive black hole binary population.

Primordial black holes and local non-Gaussianity in canonical inflation

Primordial black holes (PBHs) cannot be produced abundantly enough to be the dark matter in canonical single-field inflation under slow roll. This conclusion is robust to local non-Gaussian correlations between long- and short-wavelength curvature modes, which we show have no effect in slow roll on local primordial black hole abundances. For the prototypical model which evades this no go, ultra-slow roll (USR), these squeezed non-Gaussian correlations have at most an order unity effect on the variance of PBH-producing curvature fluctuations for models that would otherwise fail to form sufficient PBHs. Moreover, the transition out of USR, which is necessary for a successful model, suppresses even this small enhancement unless it causes a large increase in the inflaton kinetic energy in a fraction of an e-fold, which we call a large and fast transition. Along the way we apply the in-in formalism, the delta N formalism, and gauge transformations to compute non-Gaussianities and illuminate different aspects of the physical origin of these results. Local non-Gaussianity in the squeezed limit does not weaken the Gaussian conclusion that PBHs as dark matter in canonical single-field inflation require a complicated and fine-tuned potential shape with an epoch where slow roll is transiently violated.

Black hole scaling relations of active and quiescent galaxies: Addressing selection effects and constraining virial factors

Local samples of quiescent galaxies with dynamically measured black hole masses (Mbh) may suffer from an angular resolution-related selection effect, which could bias the observed scaling relations between Mbh and host galaxy properties away from the intrinsic relations. In particular, previous work has shown that the observed Mbh-Mstar (stellar mass) relation is more strongly biased than the Mbh-sigma (velocity dispersion) relation. Local samples of active galactic nuclei (AGN) do not suffer from this selection effect, as in these samples Mbh is estimated from megamasers and/or reverberation mapping-based techniques. With the exception of megamasers, Mbh-estimates in these AGN samples are proportional to a virial coefficient fvir. Direct modelling of the broad line region suggests that fvir~3.5. However, this results in a Mbh-Mstar relation for AGN which lies below and is steeper than the one observed for quiescent black hole samples. A similar though milder trend is seen for the Mbh-sigma relation. Matching the high-mass end of the Mbh-Mstar and Mbh-sigma relations observed in quiescent samples requires fvir~15 and fvir~7, respectively. On the other hand, fvir~3.5 yields Mbh-sigma and Mbh-Mstar relations for AGN which are remarkably consistent with the expected `intrinsic' correlations for quiescent samples (i.e., once account has been made of the angular resolution-related selection effect), providing additional evidence that the sample of local quiescent black holes is biased. We also show that, as is the case for quiescent black holes, the Mbh-Mstar scaling relation of AGN is driven by velocity dispersion, thus providing additional key constraints to black hole-galaxy co-evolution models.

Notes on ten-dimensional localized black holes and deconfined states in two-dimensional SYM

We numerically construct static localized black holes in ten spacetime dimensions with one compact periodic dimension. In particular, we investigate the critical regime in which the poles of the localized black hole are about to merge. When approaching the critical region, the behavior of physical quantities is described by a single real valued exponent giving rise to a logarithmic scaling of the thermodynamic quantities, in agreement with the theoretical prediction derived from the double-cone metric. As a peculiarity, the localized black hole solution in ten dimensions can be related to the spatially deconfined phase of two dimensional mathcal{N}=left(8,8right) super Yang-Mills theory (SYM) on a spatial circle. We use the localized black hole solutions to determine the SYM phase diagram. In particular, we compute the location of the first order phase confinement/deconfinement transition and the related latent heat to unprecedented accuracy.

Critical Kaluza-Klein black holes and black strings in D = 10

We construct static vacuum localized black holes and non-uniform black strings in ten spacetime dimensions, where one of the dimension is compactified on a circle. We study the phase diagram of black objects with these boundary conditions, especially near the critical point where localized black holes and non-uniform black strings merge. Remarkably, we find that the merger happens at a cusp in the phase diagram. We verify that the critical geometry is controlled by a Ricci-flat double-cone as previously predicted. However, unlike the lower dimensional cases, we find that physical quantities approach to their critical values according to a power law plus a logarithmic correction. We extract the critical exponents and find very good agreement with the predictions from the double-cone geometry. According to holography, localized black holes and black strings are dual to thermal states of (1 + 1)-dimensional SU(N) maximal Super-Yang Mills theory compactified on a circle; we recover and extend the details of the (recently found) 1st order phase transition in this system from the gravity side.

The minimum and maximum gravitational-wave background from supermassive binary black holes

The gravitational-wave background from supermassive binary black holes (SMBBHs) has yet to be detected. This has led to speculations as to whether current pulsar timing array limits are in tension with theoretical predictions. In this paper, we use electromagnetic observations to constrain the SMBBH background from above and below. To derive the {\em maximum} amplitude of the background, we suppose that equal-mass SMBBH mergers fully account for the local black hole number density. This yields a maximum characteristic signal amplitude at a period of one year $A_{\rm{yr}}<2.4\times 10^{-15}$, which is comparable to the pulsar timing limits. To derive the {\em minimum} amplitude requires an electromagnetic observation of an SMBBH. While a number of candidates have been put forward, there are no universally-accepted electromagnetic detections in the nanohertz band. We show the candidate 3C 66B implies a lower limit, which is inconsistent with limits from pulsar timing, casting doubt on its binary nature. Alternatively, if the parameters of OJ 287 are known accurately, then $A_{\rm{yr}}> 6.1\times 10^{-17}$ at 95\% confidence level. If one of the current candidates can be established as a bona fide SMBBH, it will immediately imply an astrophysically interesting lower limit.

Rotating black holes and black bars at large D

We propose and demonstrate a new and efficient approach to investigate black hole dynamics in the limit of large number of dimensions D. The basic idea is that an asymptotically flat black brane evolving under the Gregory-Laflamme instability forms lumps that closely resemble a localized black hole. In this manner, the large-D effective equations for extended black branes can be used to study localized black holes. We show that these equations have exact solutions for black-hole-like lumps on the brane, which correctly capture the main properties of Schwarzschild and Myers-Perry black holes at large D, including their slow quasinormal modes and the ultraspinning instabilities (axisymmetric or not) at large angular momenta. Furthermore, we obtain a novel class of rotating ‘black bar’ solutions, which are stationary when D → ∞, and are long-lived when D is finite but large, since their gravitational wave emission is strongly suppressed. The leading large D approximation reproduces to per-cent level accuracy previous numerical calculations of the bar-mode growth rate in D = 6, 7.

Robustness of inflation to inhomogeneous initial conditions

We consider the effects of inhomogeneous initial conditions in both the scalar field profile and the extrinsic curvature on different inflationary models. In particular, we compare the robustness of small field inflation to that of large field inflation, using numerical simulations with Einstein gravity in 3+1 dimensions. We find that small field inflation can fail in the presence of subdominant gradient energies, suggesting that it is much less robust to inhomogeneities than large field inflation, which withstands dominant gradient energies. However, we also show that small field inflation can be successful even if some regions of spacetime start out in the region of the potential that does not support inflation. In the large field case, we confirm previous results that inflation is robust if the inflaton occupies the inflationary part of the potential. Furthermore, we show that increasing initial scalar gradients will not form sufficiently massive inflation-ending black holes if the initial hypersurface is approximately flat. Finally, we consider the large field case with a varying extrinsic curvature K, such that some regions are initially collapsing. We find that this may again lead to local black holes, but overall the spacetime remains inflationary if the spacetime is open, which confirms previous theoretical studies.

Critical behavior of the black hole/black string transition

We numerically construct static localized black holes in five and six spacetime dimensions which are solutions to Einstein’s vacuum field equations with one compact periodic dimension. In particular, we investigate the critical regime in which the poles of the localized black hole are about to merge. A well adapted multi-domain pseudo-spectral scheme provides us with accurate results and enables us to investigate the phase diagram of those localized solutions within the critical regime, which goes far beyond previous results. We find that in this regime the phase diagram possesses a spiral structure adapting to the one recently found for non-uniform black strings. When approaching the common endpoint of both phases, the behavior of physical quantities is described by complex critical exponents giving rise to a discrete scaling symmetry. The numerically obtained values of the critical exponents agree remarkably well with those derived from the double-cone metric.

On the gravitational wave background from black hole binaries after the first LIGO detections

The detection of gravitational waves from the merger of binary black holes by the LIGO Collaboration has opened a new window to astrophysics. With the sensitivities of ground based detectors in the coming years, we will principally detect local binary black hole mergers. The integrated merger rate can instead be probed by the gravitational-wave background, the incoherent superposition of the released energy in gravitational waves during binary-black-hole coalescence. Through that, the properties of the binary black holes can be studied. In this work we show that by measuring the energy density ΩGW (in units of the cosmic critical density) of the gravitational-wave background, we can search for the rare ∼ 100 M⊙ massive black holes formed in the Universe. In addition, we can answer how often the least massive BHs of mass ≳ 3M⊙ form. Finally, if there are multiple channels for the formation of binary black holes and if any of them predicts a narrow mass range for the black holes, then the total ΩGW spectrum may have features that with the future Einstein Telescope can be detected.