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|Title:||Black hole X-ray binaries : radiation and high-redshift feedback|
|Authors:||Knevitt, Gillian Frances Grace|
|Presented at:||University of Leicester|
|Abstract:||The accretion of matter onto black holes results in their characteristic spectrum through which we can identify them and study their properties. Furthermore, this radiation can couple to their surroundings, resulting in complex interactions between black holes and their environments. In this thesis, I study the accreting properties of stellar mass black holes, and examine the effect that such interactions may have had on the early universe. I also consider the observational characteristics of the lowest luminosity stellar mass black hole binary systems in our own galaxy. Approximately one billion years after the Big Bang, the universe underwent a huge baryonic phase change, in which neutral hydrogen became ionized by the first sources of radiation. Massive stars are thought to drive this process, but their ionizing lifetimes could have been extended by a later phase in their evolution: black hole X-ray binary formation. However, the extent of this enhancement is not known, and has been highly debated in recent literature. In this thesis, I show that X-ray binaries were unlikely to be present in sufficient numbers to exert a significant effect on the intergalactic medium. Using a stellar population synthesis model of a single starburst event, I show that radiation from X-ray binaries dominates the ionizing power of a cluster after the most massive stars have ended their lives. However, their high energy spectra and short lifetimes mean their ionizing timescales are too long for them to affect the progress of reionization. Even so, the high escape fraction of X-rays from galaxies still provides scope for low level heating and ionization of the distant intergalactic medium under different circumstances, such as in the context of continuous star formation. I also assess the detectability of the dimmest black hole binary systems in the Milky Way. Using a catalogue of black hole binaries in our galaxy, I find that there is a statistically significant lack of short orbital period systems, when compared to the neutron star binary population. I show that these sources may be hidden from view, rather than being truly absent, due to radiatively inefficient accretion, in which energy is lost to the black hole. However, this conclusion requires that the switch to inefficient accretion occurs sharply at a threshold mass accretion rate. In the case of a smoother switch, alternative observational or evolutionary arguments must be put forward to explain this dearth.|
|Rights:||Copyright © the author. All rights reserved.|
|Appears in Collections:||Theses, Dept. of Physics and Astronomy|
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