Accretion around black holes: The geometry and spectra

TL;DR

This paper reviews the physics of accretion flows around black holes, focusing on hot and cold gas configurations and their impact on observed spectra and luminosity variations.

Contribution

It provides a comprehensive overview of the different accretion flow geometries and their dependence on accretion rates, integrating observational data with theoretical models.

Findings

Hot and cold gas configurations vary with accretion rate.

Different accretion geometries produce distinct spectral signatures.

Theoretical models explain observed luminosity variations.

Abstract

Observations of black hole X-ray binaries and active galactic nuclei indicate that the accretion flows around black holes are composed of hot and cold gas, which have been theoretically described in terms of either a hot geometrically thick corona lying above and below a cold geometrically thin disk or an inner advection dominated accretion flow connected to an outer thin disk. This article reviews the accretion flows around black holes, with an emphasis on the physics that determines the configuration of hot and cold accreting gas, and how the configuration varies with the accretion rate and thereby produces various luminosity and spectra.