Mini-discs around spinning black holes

TL;DR

This paper extends the mini-disc accretion model to spinning black holes, analyzing how black hole spin affects disc structure and efficiency, revealing a hydrodynamic Penrose process when spins are anti-aligned.

Contribution

It introduces a model for mini-discs around spinning black holes, detailing how spin influences their structure and radiative efficiency.

Findings

Disc structure depends on black hole spin.

Radiative efficiency varies with spin orientation.

Anti-aligned spins enable a hydrodynamic Penrose process.

Abstract

Accretion onto black holes in wind-fed binaries and in collapsars forms small rotating discs with peculiar properties. Such ``mini-discs'' accrete on the free-fall time without help of viscosity and nevertheless can have a high radiative efficiency. The inviscid mini-disc model was previously constructed for a non-rotating black hole. We extend the model to the case of a spinning black hole, calculate the structure and radiative efficiency of the disc and find their dependence on the black hole spin. If the angular momenta of the disc and the black hole are anti-aligned, a hydrodynamic analog of Penrose process takes place.