Accretion Of Radiation Research Articles

ACCRETION MECHANISMS ONTO PRIMORDIAL BLACK HOLES

We study the evolution of a primordial black hole (PBH) taking into account the presence of dark energy modeled by a general perfect fluid. In the specific case of a stationary non-self-gravitating test fluid, the competition between radiation accretion, Hawking evaporation and the accretion of such a fluid has been studied in detail. The evaporation of PBHs is quite modified at late times by these effects. We address further generalizations of this scenario to consider other types of fluids, and point out early developments of a nonstationary accretion model.

Cosmology with primordial black holes

We study the effect of accretion of radiation in the early universe on primordial black holes in various modified gravity theories. We consider separately, a braneworld model, Brans-Dicke theory, and a more general scalar-tensor model. The rate of growth of a primordial black hole due to accretion of radiation in all these modified gravity models is smaller than the rate of growth of the cosmological horizon, thus making available sufficient radiation density for the black hole to accrete causally. We show that accretion of radiation overrides the effect of Hawking evaporation during the radiation dominated era. The subsequent evaporation of the black holes in later eras could further be modified due to either the modified braneworld geometry, or the variable gravitational coupling in scalar-tensor theories, and they could survive up to much longer times compared to the case of standard cosmology.

Effect of accretion on primordial black holes in Brans-Dicke theory

We consider the effect of accretion of radiation in the early Universe on primordial black holes in Brans-Dicke theory. The rate of growth of a primordial black hole due to accretion of radiation in Brans-Dicke theory is considerably smaller than the rate of growth of the cosmological horizon, thus making available sufficient radiation density for the black hole to accrete causally. We show that accretion of radiation by Brans-Dicke black holes overrides the effect of Hawking evaporation during the radiation dominated era. The subsequent evaporation of the black holes in later eras is further modified due to the variable gravitational ``constant,'' and they could survive up to longer times compared to the case of standard cosmology. We estimate the impact of accretion on modification of the constraint on their initial mass fraction obtained from the $\ensuremath{\gamma}$-ray background limit from presently evaporating primordial black holes.

Primordial black holes as dark matter in alternate gravity theories

We discuss the possibility of the survival of primordial black holes as dark matter candidates in various alternate gravity theories motivated from extra-dimensional scenarios. We show that in particular, braneworld black holes, as well as black holes in scalar-tensor models can survive up to late times by efficient accretion of radiation in the early universe.

Primordial black hole: Mass and angular momentum evolution

The evolution of the primordial low mass black hole (PBH) in hot universe is considered. Increase of mass and decrease of PBH spin due to the accretion of radiation dominated matter are estimated with using of results of numerical simulation of PBH formation and approximate relations for accretion to a rotating black hole.

Evolution of primordial black holes in Jordan–Brans–Dicke cosmology

We consider the evolution of primordial black holes in a generalized Jordan-BransDicke cosmological model where both the Brans-Dicke scalar field and its coupling to gravity are dynamical functions determined from the evolution equations. The evaporation rate for the black holes is different from the case in standard cosmology. We show that the accretion of radiation can proceed effectively in the radiation dominated era. It follows that the black hole lifetime shortens for low initial mass, but increases considerably for larger initial mass, thus providing a mechanism for the survival of primordial black holes as candidates of dark matter. We derive a cut-off value for the initial black hole mass, below which primordial black holes evaporate out in the radiation dominated era, and above which they survive beyond the present era.

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.

BRANEWORLD BLACK HOLES IN COSMOLOGY AND ASTROPHYSICS

The braneworld description of our universe entails a large extra dimension and a fundamental scale of gravity that might be lower by several orders of magnitude compared to the Planck scale. An interesting consequence of the braneworld scenario is in the nature of spherically symmetric vacuum solutions to the brane gravitational field equations which could represent black holes with properties quite distinct compared to ordinary black holes in 4-dimensions. We discuss certain key features of some braneworld black hole geometries. Such black holes are likely to have diverse cosmological and astrophysical ramifications. The cosmological evolution of primordial braneworld black holes is described highlighting their longevity due to modified evaporation and effective accretion of radiation during the early braneworld high energy era. Observational abundance of various evaporation products of the black holes at different eras impose constraints on their initial mass fraction. Surviving primordial black holes could be candidates of dark matter present in galactic haloes. We discuss gravitational lensing by braneworld black holes. Observables related to the relativistic images of strong field gravitational lensing could in principle be used to distinguish between different braneworld black hole metrics in future observations.

Interacting black holes on the brane: the seeding of binaries

We consider the evolution of subhorizon-sized black holes which are formed during the high energy phase of the braneworld scenario. These black holes are long-lived due to modified evaporation and accretion of radiation during the radiation dominated era. We argue that an initial mass difference between any two neighbouring black holes is always amplified because of their exchange of energy with the surrounding radiation. We present a scheme of binary formation based on mass differences suggesting that such a scenario could lead to binaries with observable signatures.

Supermassive Black Holes May Be Limited by the Holographic Bound

Supermassive Black Holes are the most entropic objects found in the universe. The Holographic Bound (HB) to the entropy is used to constrain their formation time with initial masses ∼106−8 M ⊙, as inferred from observations. We find that the entropy considerations are more limiting than causality for this “direct” formation. Later we analyze the possibility of SMBHs growing from seed black holes. The growth of the initial mass is studied in the case of accretion of pure radiation and quintessence fields, and we find that there is a class of models that may allow this metamorphosis. Our analysis generalizes recent work for some models of quintessence capable of producing a substantial growth in a short time, while simultaneously obeying the causal and Holographic Bound limits.

Cosmic evolution and primordial black hole evaporation

A cosmological model in which primordial black holes (PBHs) are present in the cosmic fluid at some instant t=t_0 is investigated. The time t_0 is naturally identified with the end of the inflationary period. The PBHs are assumed to be nonrelativistic in the comoving fluid, to have the same mass, and may be subject to evaporation for t>t_0. Our present work is related to an earlier paper of Zimdahl and Pavon [Phys. Rev. D {\bf 58}, 103506 (1998)], but in contradistinction to these authors we assume that the (negative) production rate of the PBHs is zero. This assumption appears to us to be more simple and more physical. Consequences of the formalism are worked out. In particular, the four-divergence of the entropy four-vector in combination with the second law in thermodynamics show in a clear way how the the case of PBH evaporation corresponds to a production of entropy. Accretion of radiation onto the black holes is neglected. We consider both a model where two different sub-fluids interact, and a model involving one single fluid only. In the latter case an effective bulk viscosity naturally appears in the formalism.

Black Hole Hawking Radiation May Never Be Observed!

Thermal Hawking emission from black holes is a remarkable consequence of the unification of quantum physics and gravitation. Black holes of a few solar masses are the only ones which can form in the present universe. However, having temperatures million times smaller than the ambient cosmic background radiation they cannot evaporate. Primordial black holes of M ∼ 1014g would evaporate over a Hubble age and considerable ongoing effort is on to detect such explosions. I point out, however, that at the early universe epochs when such black holes form, the ambient radiation temperature considerably exceeds their corresponding Hawking temperature. This results in rapid continual accretion (absorption) of ambient radiation by these holes. Consequently by the end of the radiation era their masses grow much greater so that their lifetimes (scaling as M3) would now be enormously greater than the Hubble age implying undetectably small emission.

Comment on 'radiation accretion by primordial black holes in the early universe'

view Abstract Citations (9) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Comment on 'radiation accretion by primordial black holes in the early universe' Reed, B. C. ; Henriksen, R. N. Abstract The paper considers Hacyan's model (1979) for primordial black hole (PBH) growth in the early universe extended to a class of equations of state and to arbitrary time delay between the births of the universe and of the PBH. It is shown that the PBH mass grows asymptotically in proportion to the horizon mass of the background for all constant sound speeds, and that the general-relativistic matching to flat background requires that the ingoing Vaidya metric used to model the PBH be self-similar. The paths of outgoing radial photons emitted from within the PBH, showing that those emitted from within the event horizon are dragged back into the R=O singularity. Publication: The Astrophysical Journal Pub Date: March 1980 DOI: 10.1086/157751 Bibcode: 1980ApJ...236..338R Keywords: Black Holes (Astronomy); Cosmology; Interstellar Matter; Relativity; Stellar Mass Accretion; Boundary Value Problems; Galactic Evolution; Light Emission; Partial Differential Equations; Universal Time; Astrophysics full text sources ADS |

Radiation accretion by primordial black holes in the early universe

The growth of a black hole by radiation accretion in the early Universe is analyzed in the particular case in which the inflow of radiation is purely radial. This is done by generalizing the Einstein-Strauss vacuole model to the case of a radiation-filled universe. It is shown that, under this circumstance, the black hole tends to grow at the same rate as the particle horizon of the universe; this corresponds to an upper limit to the accretion rate.