Accretion into and emission from black holes

Citation

Page, Don Nelson (1976) Accretion into and emission from black holes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/RAEC-8822. https://resolver.caltech.edu/CaltechTHESIS:07192012-091529776

Abstract

Analyses are given of various processes involving matter falling into or coming out of black holes.

A significant amount of matter may fall into a black hole in a galactic nucleus or in a binary system. There gas with relatively high angular momentum is expected to form an accretion disk flowing into the hole. In this thesis the conservation laws of rest mass, energy, and angular momentum are used to calculate the radial structure of such a disk. The averaged torque in the disk and flux of radiation from the disk are expressed as explicit, algebraic functions of radius.

Matter may be created and come out of the gravitational field of a black hole in a quantum-mechanical process recently discovered by Hawking. In this thesis the emission rates of massless particles by Hawking's process are computed numerically. The resulting power spectra of neutrinos, photons, and gravitons emitted by a nonrotating hole are given. For rotating holes, the rates of emission of energy and angular momentum are calculated for various values of the rotation parameter. The evolution of a rotating hole is followed as energy and angular momentum are given up to the emitted particles. It is found that angular momentum is lost considerably faster than energy, so that a black hole spins down to a nearly nonrotating configuration before it loses a large fraction of its mass. The implications are discussed for the lifetimes and possible present configurations of primordial black holes (the only holes small enough for the emission to be significant within the present age of the universe.

As an astrophysical application, a calculation is given of the gamma-ray spectrum today from the emission by an assumed distribution of primordial black holes during the history of the universe. Comparison with the observed isotropic gamma-ray flux above about 100 MeV yields an upper limit of approximately 10^4 pc^(-3) for the average number density of holes around 5 x 10^(14)g. (This is the initial mass of a nonrotating black hole that would just decay away in the age of the universe.) The prospects are discussed for observing the final, explosive decay of an individual primordial black hole. Such an observation could test the combined predictions of general relativity and quantum mechanics and also could provide information about inhomogeneities in the early universe and about the nature of strong interactions at high temperatures.

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