Instability of Population III Black Hole Accretion Disks

TL;DR

This paper studies the stability of primordial Population III black hole accretion disks, revealing their unique instability features and potential for luminous outbursts observable by future telescopes.

Contribution

It introduces a detailed stability analysis of POP III disks, highlighting differences from solar metallicity disks and predicting observable luminosity oscillations.

Findings

POP III disks exhibit larger unstable regions in the Mdot-Sigma plane.

Quasi-periodic luminosity oscillations can occur in POP III disks.

Maximal luminosity in POP III disks exceeds that of solar metallicity disks by an order of magnitude.

Abstract

We investigate the stability of black hole accretion disks in a primordial environment (POP III disks for short), by solving the vertical structure of optically thick disks, including convective energy transport, and by employing a one-zone model for optically thin isothermal disks. Because of the absence of metals in POP III disks, we find significant differences in stability associated with ionization between POP III disks and the disks of solar metallicity. An unstable branch in S-shaped equilibrium curves on the Mdot-Sigma (mass accretion rate - surface density) plane extends to a larger surface density compared with the case of disks of solar metallicity. The resulting equilibrium loci indicate that quasi-periodic oscillations in luminosity can also be driven in POP III disks, and their maximal luminosity is typically by an order of magnitude larger than that of the disks of solar metallicity. Such a strong outburst of POP III disks can be observed by future huge telescopes, in case that the mass is supplied onto the disks at the Bondi accretion rates in typical virialized small dark halos.