Black hole X-ray Binaries

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Aurore Simonnet/Press Image for Kara et al., 2019

Stellar-mass black holes in our Galaxy

The geometry of the accretion flow around stellar-mass black holes can change on timescales of days to months (the equivalent timescale in a supermassive black hole is millions to billions of years). When a black hole emerges from quiescence it has a very hard X-ray spectrum produced by a hot corona, and then transitions to a soft spectrum dominated by emission from a geometrically thin accretion disc extending to the innermost stable circular orbit. Much debate, however, persists over how this transition occurs, whether it is driven largely by a reduction in the truncation radius of the disc or in the spatial extent of the corona. Understanding how accretion evolves in stellar-mass systems may help us understand the physics behind quasar feedback on much longer timescales.

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