Stellar Evolution in the Disks of Active Galactic Nuclei Produces Rapidly Rotating Massive Stars

TL;DR

This paper investigates how stars in active galactic nuclei disks rapidly spin up due to accretion, potentially leading to the formation of high-spin black holes and gamma-ray bursts, with implications for gravitational wave sources.

Contribution

It demonstrates that AGN stars can reach near-critical rotation rates, influencing the formation of high-spin black holes and gamma-ray bursts, a novel insight into stellar evolution in AGN environments.

Findings

AGN stars spin up to near-critical rates via accretion.

High-spin massive black holes can originate from AGN stars.

Potential link to observed gravitational wave events and gamma-ray bursts.

Abstract

Stars can either be formed in or captured by the accretion disks in Active Galactic Nuclei (AGN). These AGN stars are irradiated and subject to extreme levels of accretion, which can turn even low-mass stars into very massive ones ($M > 100 {\rm M}_\odot$) whose evolution may result in the formation of massive compact objects ($M > 10 {\rm M}_\odot$). Here we explore the spins of these AGN stars and the remnants they leave behind. We find that AGN stars rapidly spin up via accretion, eventually reaching near-critical rotation rates. They further maintain near-critical rotation even as they shed their envelopes, become compact, and undergo late stages of burning. This makes them good candidates to produce high-spin massive black holes, such as the ones seen by LIGO-Virgo in GW190521g, as well as long Gamma Ray Bursts (GRBs) and the associated chemical pollution of the AGN disk.