The Rotation of SuperMassive Stars

TL;DR

This paper models the effects of rotation on supermassive stars, exploring their stability, collapse, and potential observational signatures like gravitational waves and gamma-ray bursts, to understand their role as black hole seeds.

Contribution

It introduces the latest models of rotating supermassive stars with accretion, highlighting the impact of rotation on stability and collapse, and discusses open questions in the field.

Findings

Rotation influences SMS stability and collapse pathways.

Models suggest possible gravitational wave and gamma-ray burst signatures.

Rotation may enable SMS to serve as black hole progenitors.

Abstract

Supermassive stars (SMSs), with masses $>10^5$ M$_\odot$, have been proposed as the possible progenitors of the most extreme supermassive black holes observed at redshifts $z>6-7$. In this scenario ('direct collapse'), a SMS accretes at rates $>0.1$ M$_\odot$ yr$^{-1}$ until it collapses to a black hole via the general-relativistic (GR) instability. Rotation plays a crucial role in the formation of such supermassive black hole seeds. The centrifugal barrier appears as particularly strong in this extreme case of star formation. Moreover, rotation impacts sensitively the stability of SMSs against GR, as well as the subsequent collapse. In particular, it might allow for gravitational wave emission and ultra-long gamma-ray bursts at black hole formation, which represents currently the main observational signatures proposed in the literature for the existence of such objects. Here, I present the latest models of SMSs accounting for accretion and rotation, and discuss some of the open questions and future prospects in this research line.