Dark matter density spikes around primordial black holes

We show that density spikes begin to form from dark matter particles around primordial black holes immediately after their formation at the radiation-dominated cosmological stage. This stems from the fact that in the thermal velocity distribution of particles there are particles with low velocities that remain in finite orbits around black holes and are not involved in the cosmological expansion. The accumulation of such particles near black holes gives rise to density spikes. These spikes are considerably denser than those that are formed later by the mechanism of secondary accretion. The density spikes must be bright gamma-ray sources. Comparison of the calculated signal from particle annihilation with the Fermi-LAT data constrains the present-day cosmological density parameter for primordial black holes with masses M _BH ≥ 10^?8 M _⊙ from above by values from Ω_BH ≤ 1 to Ω_BH ≤ 10?8, depending on MBH. These constraints are several orders of magnitude more stringent than other known constraints.     

Clusters of black holes as point-like gamma-ray sources

The possibility of identifying some of Galactic gamma-ray sources as clusters of primordial black holes is discussed. The known scenarios of supermassive black hole formation indicate the multiple formation of lower-mass black holes. Our analysis demonstrates that due to Hawking evaporation the cluster of black holes with masses about 10¹⁵ g could be observed as a gamma-ray source. The total mass of typical cluster is ∼10 M_⊙. Detailed calculations have been performed on the basis of specific model of primordial black hole formation.     

Accretion history of active black holes from type 1 AGN

Almost all galaxies have massive central black holes in their centers with masses typically ranging from ～10⁵ to ～10⁹ M_⊙. However, the origin and evolution of these objects and their connection with the hosting galaxies are not completely understood yet. In this work we analyze the mass accretion rate of supermassive black holes (SMBH’s) and the mean Eddington ratio (MER) of type 1 AGN using data from the Sloan Sky Survey. For this purpose we improve the method for constructing the subsample of SMBH, taking into account the survey flux limit and the bias of the sample. It was observed that the mean bolometric luminosity of the active black holes can be represented by a function composed by a power law in mass and a like-Schechter function in redshift. Our results also show that both the mean Eddington ratio and the mass accretion rate are proportional to this function.     

Some implications of escape of supermassive black holes from galactic nuclei due to plasmoid ejection

Shklovsky (1982) has hypothesized escape of accreting supermassive black holes from galactic nuclei as a consequence of asymmetric ejection of plasma clouds from their accretion disks and their subsequent defunction for explaining evolutionary effects in quasars. It has been argued here that such an interpretation must accomodate the possibility of substantial capture of stars and gas by the black hole on its way out-which can prolong the life of the quasar-unless the mass of the black hole is less than ～10⁷ M _⊙ and a large enough initial recoil velocity is achieved.     

X-ray emission from accretion disks in active galactic nuclei

We constructed a grid of relativistic models for standard high-relative-luminosity accretion α-disks around supermassive Kerr black holes (BHs) and computed X-ray spectra for their hot, effectively optically thin inner parts by taking into account general-relativity effects. They are known to be heated to high (～10⁶–10⁹ K) temperatures and to cool down through the Comptonization of intrinsic thermal radiation. Their spectra are power laws with an exponential cutoff at high energies; i.e., they have the same shape as those observed in active galactic nuclei (AGNs). Fitting the observed X-ray spectra of AGNs with computed spectra allowed us to estimate the fundamental parameters of BHs (their mass and Kerr parameter) and accretion disks (luminosity and inclination to the line of sight) in 28 AGNs. We show that the Kerr parameter for BHs in AGNs is close to unity and that the disk inclination correlates with the Seyfert type of AGN, in accordance with the unification model of activity. The estimated BH masses M_x are compared with the masses M_rev determined by the reverberation mapping technique. For AGNs with luminosities close to the Eddington limit, these masses agree and the model under consideration may be valid for them. For low-relative-luminosity AGNs, the differences in masses increase with decreasing relative luminosity and their X-ray emission cannot be explained by this model.     

High-redshift objects as probes of nearby cosmic voids

We show that present day observational techniques make it possible to detect diffuse gas masses down to ～10¹⁰ M _⊙ in cosmic voids with linear sizes of ～1 Mpc or larger. The observations consist of searches for absorption lines, similar in character to those produced in galactic interstellar clouds, in the spectra of high-redshift objects located beyond previously identified voids adjoining nearby superclusters.     

Bridging the gap between stellar-mass black holes and ultraluminous X-ray sources

The X-ray spectral and timing properties of ultraluminous X-ray sources (ULXs) have many similarities with the very high state of stellar-mass black holes (power-law dominated, at accretion rates greater than the Eddington rate). On the other hand, their cool disk components, large characteristic inner-disk radii and low characteristic timescales have been interpreted as evidence of black hole masses ～1000 M _⊙ (intermediate-mass black holes). Here we re-examine the physical interpretation of the cool disk model, in the context of accretion states of stellar-mass black holes. In particular, XTE J1550–564 can be considered the missing link between ULXs and stellar-mass black holes, because it exhibits a high-accretion-rate, low-disk-temperature state (ultraluminous branch). On the ultraluminous branch, the accretion rate is positively correlated with the disk truncation radius and the bolometric disk luminosity, while it is anti-correlated with the peak temperature and the frequency of quasi-periodic-oscillations. Two prototypical ULXs (NGC?1313 X-1 and X-2) also seem to move along that branch. We use a phenomenological model to show how the different range of spectral and timing parameters found in the two classes of accreting black holes depends on both their masses and accretion rates. We suggest that ULXs are consistent with black hole masses ～50–100 M _⊙, moderately inefficiently accreting at ≈20 times Eddington.     

Shaping the relation between the mass of supermassive black holes and the velocity dispersion of galactic bulges

I use the fact that the radiation emitted by the accretion disk of supermassive black hole can heat up the surrounding gas in the protogalaxy to achieve hydrostatic equilibrium during the galaxy formation. The correlation between the black hole mass M _BH and velocity dispersion σ thus naturally arises. The result generally agrees with empirical fittings from observational data, even with M _BH ≤10⁶ M _⊙. This model provides a clear picture on how the properties of the galactic supermassive black holes are connected with the kinetic properties of the galactic bulges.     

Bursts of gravitational radiation from active galactic nuclei and globular clusters

The characteristics of gravitational bursts from active galactic nuclei, and globular clusters are obtained for three astrophysical situations:(i) scattering of stars by massive black holes residued at the centers of galaxies and globular clusters; (ii) the close encounters of stars in the nuclear regions of these objects; (iii) scattering of stars by black holes of stellar mass containing in the stellar population of galactic nuclei and clusters. The most effective source of gravitational bursts appears to be a scattering of stars by the massive central black holes which produces the bursts with dimensionless amplitudeh10^–19–10^–21 and frequencies from 10^–1 to 10^–5 Hz. The characteristics obtained correspond to the possiblities of a future gravitational-wave experiment with use of laser Doppler tracking of interplanetary spacecrafts.     

Life-bearing primordial planets in the solar vicinity

The space density of life-bearing primordial planets in the solar vicinity may amount to ～8.1×10⁴?pc^?3 giving total of ～10¹⁴ throughout the entire galactic disk. Initially dominated by H₂ these planets are stripped of their hydrogen mantles when the ambient radiation temperature exceeds 3?K as they fall from the galactic halo to the mid-plane of the galaxy. The zodiacal cloud in our solar system encounters a primordial planet once every 26 My (on our estimate) thus intercepting an average mass of 10³ tonnes of interplanetary dust on each occasion. If the dust included microbial material that originated on Earth and was scattered via impacts or cometary sublimation into the zodiacal cloud, this process offers a way by which evolved genes from Earth life could become dispersed through the galaxy.     

A simple model for the evaporation of black holes at final stages

We present a simple model for the evaporation of primordial black holes at final stages with the formation of a relic remnant with a mass of 1–10³ m _P1. The model takes into account the conservation of energy and the impossibility of passing through the state with the minimum possible mass. These relic remnants may account for a substantial fraction of dark matter in the Universe.     

Neutrino radiation from a collapsing galactic nucleus

We discuss the possible observational manifestation of the formation of massive black holes in galactic nuclei in the form of an intense high-energy neutrino flux. A short-lived (≤10 yr) hidden neutrino source results from the natural dynamicalal evolution of a central star cluster in the galactic nucleus before its gravitational collapse. The central star cluster at the final evolutionary stage consists of degenerate compact stars (neutron stars and stellar-mass black holes) and is embedded in a massive gaseous envelope produced by destructive collisions of normal stars. Multiple fireballs from frequent collisions of neutron stars give rise to a tenuous quasi-stationary cavity in the central part of the massive envelope. The cavity is filled with shock waves on which an effective cosmic-ray acceleration takes place. Allthe accelerated particles, except the secondary high-energy neutrinos, are absorbed in the dense envelope. The neutrino signal that carries information on the dynamicals of the collapsing galactic nucleus can be recorded by a neutrino detector with an effective area S∼1 km².     

A note on gravitational memory in F(R)-theories and their equivalent scalar-tensor theories

In this paper we consider the implications that the effect gravitational memory would have on primordial black holes, within the theoretical context of F(R) related scalar-tensor theories. As we will demonstrate, under the assumption that the initial mass of the primordial black hole is such so that it evaporates today, this can potentially constrain the F(R) related theories of gravity. We study two scalar-tensor models and discuss the evolution of primordial black holes created at some initial time t _f in the early universe. The results between the two models vary significantly which shows us that, if the effect of gravitational memory is considered valid, some of the scalar-tensor models and their corresponding F(R) theories must be further constrained.     

Searching for very-high-energy gamma-ray bursts from evaporating primordial black holes

Temporal and energy characteristics of the very-high-energy gamma-ray bursts from evaporating primordial black holes have been calculated by assuming that the photospheric and chromospheric effects are negligible. The technique of searching for such bursts on shower arrays is described. We show that the burst time profile and the array dead time should be taken into account to interpret experimental data. Based on data from the Andyrchy array of the Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences), we have obtained an upper limit on the number density of evaporating primordial black holes in a local region of space with a scale size of ～10^?3 pc. Comparison with the results of previous experiments is made.     

Extrapolating SMBH correlations down the mass scale: the case for IMBHs in globular clusters

Empirical evidence for both stellar mass black holes (M _•<10²  M _⊙) and supermassive black holes (SMBHs, M _•>10⁵  M _⊙) is well established. Moreover, every galaxy with a bulge appears to host a SMBH, whose mass is correlated with the bulge mass, and even more strongly with the central stellar velocity dispersion σ _c , the M _•–σ relation. On the other hand, evidence for “intermediate-mass” black holes (IMBHs, with masses in the range 100–10⁵ M _⊙) is relatively sparse, with only a few mass measurements reported in globular clusters (GCs), dwarf galaxies and low-mass AGNs. We explore the question of whether globular clusters extend the M _•–σ relationship for galaxies to lower black hole masses and find that available data for globular clusters are consistent with the extrapolation of this relationship. We use this extrapolated M _•–σ relationship to predict the putative black hole masses of those globular clusters where existence of central IMBH was proposed. We discuss how globular clusters can be used as a constraint on theories making specific predictions for the low-mass end of the M _•–σ relation.     

Magnetic fields and quasi-periodic oscillations of black hole radiation

Various relations are found between the key parameters of black holes and active galactic nuclei. Some have a statistical property, others follow from the theoretical consideration of the evolution of these objects. In this paper we use a recently discovered empirical relation between the characteristic frequency of quasi-periodic oscillations of radiation ν _br of black holes, their masses and matter accretion rates to determine the magnetic field strength B _H at the black hole event horizon. Since the characteristic frequency can be determined from observations, the use of a new relation for the estimations of magnetic field B _H can yield more definite results, since we are decreasing the number of the unknown or poorly-determined parameters of objects (it especially concerns the accretion rate Ṁ). The typical values which we have found are B _H ≃ 10⁸G for the stellar mass black holes, and B _H ≃ 10⁴G for the supermassive black holes. Besides, we demonstrate that if the linear polarization of an object is caused by the radiation of a magnetized accretion disk, then the degree of observable polarization is p ∼ ν _br ^−1/2.     

Gravitational wave bursts from collisions of primordial black holes in clusters

The rate of gravitational wave bursts from the mergers of massive primordial black holes in clusters is calculated. Such clusters of black holes can be formed through phase transitions in the early Universe. The central black holes in clusters can serve as the embryos of supermassive black holes in galactic nuclei. The expected burst detection rate by the LISA gravitational wave detector is estimated.     

Goals of the ARISE space VLBI mission

Supermassive black holes, with masses of 10⁶ M to more than 10⁹ M, are among the most spectacular objects in the Universe, and are laboratories for physics in extreme conditions. The primary goal of ARISE (Advanced Radio Interferometry between Space and Earth) is to use the technique of Space VLBI to increase our understanding of black holes and their environments, by imaging the havoc produced in the near vicinity of the black holes by their enormous gravitational fields. The mission will be based on a 25-meter space-borne radio telescope operating at frequencies between 8 and 86 GHz, roughly equivalent to an orbiting element of the Very Long Baseline Array. In an elliptical orbit with an apogee height of 40 000–100 000 km, ARISE will provide a resolution of 15 microarcsecond or better, 5–10 times better than that achievable on the ground. At frequencies of 43 and 86 GHz, the resolution of light weeks to light months in distant quasars will complement the gamma-ray and X-ray observations of high-energy photons, which come from the same regions near the massive black holes. At 22 GHz, ARISE will image the H₂O maser disks in active galaxies more than 15 Mpc from Earth, probing accretion physics and giving accurate measurements of black-hole masses. ARISE also will study gravitational lenses at resolutions of tens of microarcseconds, yielding important information on the dark-matter distribution and on the possible existence of compact objects with masses of 10³ M to 10⁶ M.     

A Fundamental Plane of Black Hole Activity: Pushing Forward the Unification Scheme

We examine the disc-jet connection in stellar mass and supermassive black holes by investigating the properties of their compact emission in the hard X-ray and radio bands. We compile a sample of ∼100 active galactic nuclei with measured mass, 5 GHz core emission, and 2–10 keV luminosity, together with eight galactic black holes with a total of ∼50 simultaneous observations in the radio and X-ray bands. Using this sample, we study the correlations between the radio (L_R) and the X-ray (L_X) luminosity and the black hole mass (M). We find that the radio luminosity is correlated with both M and L_X, at a highly significant level. We show how this result can be used to extend the standard unification by orientation scheme to encompass unification by mass and accretion rate.     

The minimum masses of black holes from the generalized uncertainty principle and the uncertainty principle

In this paper we compare the minimum masses of Schwarzschild black hole obtained from the generalized uncertainty principle and the Heisenberg uncertainty principle. Three minimum masses are obtained. The first two are the order of Planck mass which can be normally accepted. The last one based on Scardigli’s hypothesis and consideration is about M _c ?10¹⁵ g～10²⁰ M _pl which may be problematic. Whether right or wrong, it needs the astronomical observations.