Disc accretion onto a binary black hole in a hierarchical triple system as an origin of the most luminous hyper-soft sources

TL;DR

This paper proposes that luminous hypersoft X-ray sources are caused by accretion onto a binary black hole within a hierarchical triple system, explaining their extreme luminosity and spectral properties.

Contribution

It introduces a new model linking hierarchical triple systems with luminous hypersoft X-ray sources, emphasizing accretion dynamics in such systems.

Findings

Accretion onto binary black holes can produce the observed X-ray luminosities.

Orbital parameters consistent with observed source properties.

Circumbinary accretion disc explains spectral features.

Abstract

We propose that the recently discovered luminous hypersoft X-ray sources can be explained by accretion onto a binary black hole in a hierarchical triple system. For black hole masses $\sim 15 M_\odot$, the orbital separation of the internal binary might be $\sim 0.01 $~AU. If the donor provides $\gtrsim 10^{-8} M_\odot$ yr$^{-1}$, then the circumbinary accretion disc can explain the observed properties of the most luminous supersoft sources.