On the Magnetic Prandtl Number Behavior of Accretion Disks

TL;DR

This paper explores how the magnetic Prandtl number varies in accretion disks, especially near compact objects, and discusses its potential impact on turbulence and state changes in X-ray sources.

Contribution

It provides an analysis of the magnetic Prandtl number behavior in accretion disks and links it to turbulence levels and astrophysical phenomena.

Findings

Magnetic Prandtl number can exceed unity within 50 Schwarzschild radii.

Turbulence levels depend on the Prandtl number, affecting accretion dynamics.

Potential explanation for state changes in X-ray sources.

Abstract

We investigate the behavior of the magnetic Prandtl number (ratio of microscopic viscosity to resistivity) for accretion sources. Generally this number is very small in standard accretion disk models, but can become larger than unity within $\sim 50$ Schwarzschild radii of the central mass. Recent numerical investigations suggest a marked dependence of the level of MHD turbulence on the value of the Prandtl number. Hence, black hole and neutron star accretors, i.e. compact X-ray sources, are affected. The astrophysical consequences of this could be significant, including a possible route to understanding the mysterious state changes that have long characterized these sources.