Reconnection in Marginally Collisionless Accretion Disk Coronae

TL;DR

This paper discusses how the plasma in accretion disk coronae around black holes is likely marginally collisionless, enabling fast magnetic reconnection, which impacts the understanding of their X-ray emission.

Contribution

It links observational features of black hole coronae with plasma physics, proposing that marginally collisionless states facilitate fast reconnection.

Findings

Coronal plasma is likely marginally collisionless.

Fast reconnection occurs only in collisionless plasmas.

Implications for X-ray emission mechanisms in black hole accretion disks.

Abstract

We point out that a conventional construction placed upon observations of accreting black holes, in which their nonthermal X-ray spectra are produced by inverse comptonization in a coronal plasma, suggests that the plasma is marginally collisionless. Recent developments in plasma physics indicate that fast reconnection takes place only in collisionless plasmas. As has recently been suggested for the Sun's corona, such marginal states may result from a combination of energy balance and the requirements of fast magnetic reconnection.