Accretion,primordial black holes and standard cosmology

Primordial black holes evaporate due to Hawking radiation. We find that the evaporation times of primordial black holes increase when accretion of radiation is included. Thus, depending on accretion efficiency, more primordial black holes are existing today, which strengthens the conjecture that the primordial black holes are the proper candidates for dark matter.     

Nonthermal radiation of rotating black holes

The nonthermal radiation of a Kerr black hole is considered as the tunneling of particles being produced through an effective Dirac gap. In the leading semiclassical approximation, this approach is also applicable to bosons. Our semiclassical results for photons and gravitons are consistent with those obtained previously. For neutrinos, the result of our complete quantum-mechanical calculation is about twice as large as the previous one.     

Evolution of primordial black holes in a radiation and phantom energy environment

In this work we extend previous work on the evolution of a primordial black hole (PBH) to address the presence of a dark energy component with a super-negative equation of state as a background, investigating the competition between the radiation accretion, the Hawking evaporation and the phantom accretion, the latter two causing a decrease on black hole mass. It is found that there is an instant during the matter-dominated era after which the radiation accretion becomes negligible compared to the phantom accretion. The Hawking evaporation may become important again depending on a mass threshold. The evaporation of PBHs is quite modified at late times by these effects, but only if the generalized second law of thermodynamics is violated.     

Distorted rotating black holes

An axisymmetric stationary metric which describes rotating black holes distorted by surrounding matter is presented by means of the inverse scattering problem technique, and is written down explicitly in terms of the Legendre polynomials. A mass formula for the distorted holes is derived via the Komar integrals over the horizon.     

Baryon production by primordial black holes

The evaporation of primordial black holes (PBH's) by the Hawking process can produce an excess of baryons over anti-baryons. Assuming a power-law form of the initial mass spectrum of PBH's and taking into account the observational constraints on that spectrum we calculate the baryon excess produced. We find that if the spectrum is steep ($\text{α?3.5}$) or cut off for masses above ～ 10⁹ g, the observed baryon/photon ratio of ～ 10^?9 can be produced by PBH evaporations.     

Gauge and gravitational anomalies and Hawking radiation of rotating BTZ black holes

In this paper we obtain the flux of Hawking radiation from rotating BTZ black holes from the gauge and gravitational anomalies point of view. Then we show that the gauge and gravitational anomaly in BTZ spacetime is cancelled by the total flux of a 2-dimensional blackbody at the Hawking temperature of the spacetime.     

Gamma-ray bursts from evaporating primordial black holes

It is believed that the detection of gamma-ray bursts from evaporating primordial black holes is highly improbable in the near future since the expected photon flux, consisting mainly of photons with energies ? GeV, is too low. Contrary to this point of view, we show that a large fraction of the black hole power at the final stage of evaporation (the last 10³ s) can be liberated as a burst of soft γ-ray emission of duration 10^?1–10³ s and luminosity 10²⁸–10³¹ erg/s in the energy range 0.1–1 MeV. According to our calculations of the black hole evaporation rate (within the Standard Model of elementary particles), when the black hole temperature exceeds approximately 10 GeV, the charged particle outflow from a black hole forms a well-defined plasma and can be described in the hydrodynamic approximation. In this case more than half of the rest energy of a black hole can be converted into soft gamma-rays due to the presence of the magnetic field with energy density comparable to that of charged particles. We consider various mechanisms leading to such transformation and estimate their efficiency. It is shown that, at least, some of the gamma-ray bursts detected by BATSE can be associated with evaporating black holes.     

Astrophysical structures from primordial quantum black holes

The characteristic sizes of astrophysical structures, up to the whole observed Universe, can be recovered, in principle, assuming that gravity is the overall interaction assembling systems starting from microscopic scales, whose order of magnitude is ruled by the Planck length and the related Compton wavelength. This result agrees with the absence of screening mechanisms for the gravitational interaction and could be connected to the presence of Yukawa corrections in the Newtonian potential which introduce typical interaction lengths. This result directly comes out from quantization of primordial black holes and then characteristic interaction lengths directly emerge from quantum field theory.     

NANOGrav hints on planet-mass primordial black holes

Recently, the North American Nanohertz Observatory for Gravitational Waves(NANOGrav) claimed the detection of a stochastic common-spectrum process of the pulsar timing array(PTA) time residuals from their 12.5 year data, which might be the first detection of the stochastic background of gravitational waves(GWs). We show that the amplitude and the power index of such waves imply that they could be the secondary GWs induced by the peaked curvature perturbation with a dust-like post inflationary era with-0.091 ≤ w ≤ 0.048. Such stochastic background of GWs naturally predicts substantial existence of planet-mass primordial black holes(PBHs), which can be the lensing objects for the ultrashort-timescale microlensing events observed by the Optical Gravitational Lensing Experiment(OGLE).     

Gamma-ray bursts from evaporating primordial black holes

It is believed that the detection of gamma-ray bursts from evaporating primordial black holes is highly improbable in the near future since the expected photon flux, consisting mainly of photons with energies ≳ GeV, is too low. Contrary to this point of view, we show that a large fraction of the black hole power at the final stage of evaporation (the last 10³ s) can be liberated as a burst of soft γ-ray emission of duration 10⁻¹–10³ s and luminosity 10²⁸–10³¹ erg/s in the energy range 0.1–1 MeV. According to our calculations of the black hole evaporation rate (within the Standard Model of elementary particles), when the black hole temperature exceeds approximately 10 GeV, the charged particle outflow from a black hole forms a well-defined plasma and can be described in the hydrodynamic approximation. In this case more than half of the rest energy of a black hole can be converted into soft gamma-rays due to the presence of the magnetic field with energy density comparable to that of charged particles. We consider various mechanisms leading to such transformation and estimate their efficiency. It is shown that, at least, some of the gamma-ray bursts detected by BATSE can be associated with evaporating black holes. Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 1, pp. 36–45, January, 1998.     

Thermodynamics of rotating regular black holes

This paper presents a study on the thermodynamics of rotating Bardeen as well as Hayward regular black hole and their anti-de Sitter versions. We analyze the temperature, entropy, heat capacity and thermodynamical stability for the considered black hole geometries. The Hawking temperature is calculated using the surface gravity as well as tunneling probability method leading to the same result. We conclude that the considered rotating as well as rotating anti-de Sitter regular black holes are less hot and thermodynamically more stable than ordinary Kerr and Kerr-anti-de Sitter solutions, respectively.     

Accretion on high derivative asymptotically safe black holes

Asymptotically safe gravity is an effective approach to quantum gravity.It is important to differentiate modified gravity,which is inspired by asymptotically safe gravity.In this study,we examine particle dynamics near the improved version of a Schwarzschild black hole.We assume that in the context of an asymptotically safe gravity scenario,the ambient matter surrounding the black hole is of isothermal nature,and we investigate the spherical accretion of matter by deriving solutions at critical points.The analysis of various values of the state parameter for isothermal test fluids,viz.,k=1,1/2,1/3,1/4 show the possibility of accretion onto an asymptotically safe black hole.We formulate the accretion problem as Hamiltonian dynamical system and explain its phase flow in detail,which reveals interesting results in the asymptotically safe gravity theory.     

Transient solar oscillations driven by primordial black holes

Stars are transparent to the passage of primordial black holes (PBHs) and serve as seismic detectors for such objects. The gravitational field of a PBH squeezes a star and causes it to ring acoustically. We calculate the seismic signature of a PBH passing through the Sun. The background for this signal is the observed spectrum of solar oscillations excited by supersonic turbulence. We predict that PBHs more massive than 10(21) g (comparable in mass to an asteroid) are detectable by existing solar observatories. The oscillations excited by PBHs peak at large scales and high frequencies, making them potentially detectable in other stars. The discovery of PBHs would have profound implications for cosmology and high-energy physics.