Behaviour of relativistic black hole accretion sufficiently close to the horizon

TL;DR

This paper develops a new formalism for analyzing matter accretion onto rotating black holes, revealing how black hole spin influences near-horizon flow behavior and potential spectral signatures.

Contribution

Introduces a novel formalism for relativistic hydrodynamic accretion in Kerr spacetime, including stationary solutions and shock formation analysis near the horizon.

Findings

Flow can be multi-transonic with shock formation.

Black hole spin affects near-horizon matter properties.

Potential spectral signatures linked to black hole spin.

Abstract

This work introduces a novel formalism to investigate the role of the spin of astrophysical black holes in determining the behaviour of matter falling onto such accretors. Equations describing the general relativistic hydrodynamic accretion flow in the Kerr metric are formulated, and stationary solutions for such flow equations are provided. The accreting matter may become multi-transonic, allowing a stationary shock to form for certain initial boundary conditions. Such a shock determines the disc geometry and can drive strong outflows. The properties of matter extremely close to the event horizon are studied as a function of the Kerr parameter, leading to the possibility of detecting a new spectral signature of black hole spin.