We consider the observational constraints on stupendously large black holes (SLABs) in the mass range $M \gtrsim 10^{11}\,M_{\odot}$. These have attracted little attention hitherto and we are aware of no published constraints on a SLAB population in the range $(10^{12}$ - $10^{18})\,M_{\odot}$. However, there is already evidence for black holes of up to nearly $10^{11}\,M_{\odot}$ in galactic nuclei, so it is conceivable that SLABs exist and they may even have been seeded by primordial black holes. We focus on limits associated with (i) dynamical and lensing effects, (ii) the generation of background radiation through the accretion of gas during the pregalactic epoch, and (iii) the gamma-ray emission from the annihilation of the halo of weakly interacting massive particles (WIMPs) expected to form around each SLAB if these provide the dark matter. Finally, we comment on the constraints on the mass of ultra-light bosons from future measurements of the mass and spin of SLABs.
We give an explanation for the signal detected by NANOGrav as the stochastic gravitational wave background from binary mergers of primordial "Stupendously Large Black Holes" (SLABs) of mass $M\sim(10^{11}-10^{12})M_{\odot}$, and corresponding to roughly $0.1\%$ of the dark matter. We show that the stringent bounds coming from $μ$ distortions of the CMB can be surpassed if the perturbations resulting in these BHs arise from the non-Gaussian distribution of fluctuations expected in single field models of inflation generating a spike in the power spectrum. While the tail of the stochastic backgro…
In a variety of mechanisms generating primordial black holes, each black hole is expected to form along with a surrounding underdense region that roughly compensates the black hole mass. This region will propagate outwards and expand as a shell at the speed of sound in the homogeneous background. Dissipation of the shell due to Silk damping could lead to detectable $μ$-distortion in the CMB spectrum. While the current bound on the average $μ$-distortion is $\left| \barμ\right|\lesssim10^{-4}$, the standard $Λ$CDM model predicts $\left| \barμ\right|\sim10^{-8}$, which could possibly be detected…
We review the formation and evaporation of primordial black holes (PBHs) and their possible contribution to dark matter. Various constraints suggest they could only provide most of it in the mass windows $10^{17}$ - $10^{23}\,$g or $10$ - $10^{2}\,M_{\odot}$, with the last possibility perhaps being suggested by the LIGO/Virgo observations. However, PBHs could have important consequences even if they have a low cosmological density. Sufficiently large ones might generate cosmic structures and provide seeds for the supermassive black holes in galactic nuclei. Planck-mass relics of PBH evaporatio…
Although the dark matter is usually assumed to be some form of elementary particle, primordial black holes (PBHs) could also provide some of it. However, various constraints restrict the possible mass windows to $10^{16}$ - $10^{17}\,$g, $10^{20}$ - $10^{24}\,$g and $10$ - $10^{3}\,M_{\odot}$. The last possibility is contentious but of special interest in view of the recent detection of black-hole mergers by LIGO/Virgo. PBHs might have important consequences and resolve various cosmological conundra even if they have only a small fraction of the dark-matter density. In particular, those larger…
Observations of gravitational waves and their electromagnetic counterparts may soon uncover the existence of coalescing compact binary systems formed by a stellar-mass black hole and a neutron star. These mergers result in a remnant black hole, possibly surrounded by an accretion disk. The mass and spin of the remnant black hole depend on the properties of the coalescing binary. We construct a map from the binary components to the remnant black hole using a sample of numerical-relativity simulations of different mass ratios $q$, (anti-)aligned dimensionless spins of the black hole $a_{\rm BH}$…
Axion-like particles (ALPs), a compelling candidate for dark matter (DM), are the pseudo Nambu-Goldstone bosons of a spontaneously and explicitly broken global $U(1)$ symmetry. When the symmetry breaking happens after inflation, the ALP cosmology predicts the formation of a string-wall network which must annihilate early enough, producing gravitational waves (GWs) and primordial black holes (PBHs), as well as non-relativistic ALPs. We call this process catastrogenesis. We show that, under the generic assumption that the potential has several degenerate minima, GWs from string-wall annihilation…
Masking of black holes means that, for given total mass and Hawking temperatures, these data may correspond to either "pure" black hole or a black hole of a lesser mass surrounded by a massive shell. It is shown that there is one-to one correspondence between this phenomenon and thermodynamics of a black hole in a finite size cavity: masking of black holes is possible if and only if there exists at least one locally unstable black hole solution in the corresponding canonical ensemble.
We define and calculate the "discharge mode" for a Schwarzschild black hole in massive electrodynamics. For small photon mass, the discharge mode describes the decay of the electric field of a charged star collapsing into a black hole. We argue that a similar "discharge of mass" occurs in massive gravity and leads to a strange process of black hole disappearance.
We develop an analytic formalism for computing the merger rate of primordial black hole binaries with a general mass function by taking into account the torques by the surrounding primordial black holes and linear density perturbations. We find that $α=-(m_{i}+m_{j})^2\partial^{2} \ln {\mathcal R}(m_{i},m_{j})/\partial m_{i} \partial m_{j}=36/37$ is independent of the mass function. Moreover, the ratio of the merger rate density of primordial black hole binaries by taking into account the torques by the surrounding primordial black holes to by the nearest primordial black hole is independent o…
This article documents our ongoing search for the elusive "intermediate-mass" black holes. These would bridge the gap between the approximately ten solar mass "stellar-mass" black holes that are the end-product of the life of a massive star, and the "supermassive" black holes with masses of millions to billions of solar masses found at the centers of massive galaxies. The discovery of black holes with intermediate mass is the key to understanding whether supermassive black holes can grow from stellar-mass black holes, or whether a more exotic process accelerated their growth only hundreds of m…
In this paper, the merger rate of black holes in a cluster of primordial black holes (PBHs) is investigated. The clusters have characteristics close to those of typical globular star clusters. A cluster that has a wide mass spectrum ranging from $10^{-2}$ to $10 \, M_{\odot}$ (Solar mass) and contains a massive central black hole of the mass $M_{\bullet} = 10^3 \, M_{\odot}$ is considered. It is shown that in the process of the evolution of cluster, the merger rate changed significantly, and by now, the PBH clusters have passed the stage of active merging of the black holes inside~them.
Black hole is called optimal if information content is minimal at the University region, consisting of usual substance and one(n) black hole(s). Optimal black hole mass does not depend on the mass of the Universe region. Optimal black holes can exist when at least the two types of substance are available in the Universe: with non-linear and linear correspondence between information content and mass. Information content of optimal black hole is proportional to squared coefficient correlating information content with mass in usual substance and in inverse proportion to coefficient correlating in…
A simple refinement is proposed to the Dibai method for determining black hole masses in type-1 thermal AGNs. Comparisons with reverberation mapping black hole masses and host galaxy bulge properties suggest that the method is accurate to +/- 0.15 dex. Contrary to what was thought when the black hole mass - stellar velocity dispersion ("M - sigma") relationship was first discovered, it does not have a lower dispersion than the black hole mass - bulge luminosity ("M - L") relationship. The dispersion in the M - L relationship for AGNs decreases strongly with increasing black hole mass or bulge …
In this paper we determined values of a spin of central black holes of the intermediate masses in globular clusters. For determination of value of a spin we used the known relation between the kinetic power of the relativistic jet and observable radio-luminosity of the region near to a central black hole, and our estimates have based on the known Blandford-Znajek mechanism. The value of a magnetic field strength near the event horizon of a black hole was derived via magnetic coupling mechanism. Accretion rate was derived using Bondi-Hoyle mechanism.
One of the key open questions in cosmology today pertains to understanding when, where and how super massive black holes form, while it is clear that mergers likely play a significant role in the growth cycles of black holes, how supermassive black holes form, and how galaxies grow around them. Here, we present Hubble Space Telescope WFC3/IR grism observations of a clumpy galaxy at z=1.35, with evidence for 10^6 - 10^7 Msun rapidly growing black holes in separate sub-components of the host galaxy. These black holes could have been brought into close proximity as a consequence of a rare multipl…
