Little Red Dots As Late-stage Quasi-stars

TL;DR

The paper proposes that the recently observed 'Little Red Dots' are late-stage quasi-stars, which are massive objects with black holes accreting from envelopes, crucial for understanding supermassive black hole formation.

Contribution

It links LRDs to late-stage quasi-star models, showing their spectral and physical properties match predictions, suggesting LRDs are a phase in supermassive black hole evolution.

Findings

LRDs are consistent with late-stage quasi-star models.

Spectral features include reddish colors and broad Balmer lines.

X-ray suppression due to high electron densities.

Abstract

We argue that the "Little Red Dots" (LRDs) discovered with the James Webb Space Telescope are quasi-stars in their late stages of evolution. Quasi-stars are hypothetical objects predicted to form following the core collapse of supermassive stars, and consist of black holes accreting from massive envelopes at a super-Eddington rate. We show that models of late-stage quasi-stars, with black hole masses exceeding $\sim 10\%$ of the total, predict thermal and radiative properties that are insensitive to both black hole and envelope mass, and spectrally resemble LRDs. Specifically, we show that they are likely to exhibit reddish colors, a strong Balmer break, and possess conditions favorable to the production of Balmer lines that are broadened by electron scattering. Their huge electron column densities suppress any X-rays. Late-stage quasi-stars, with black hole masses $\gtrsim 10^6 M_\odot$, should dominate the overall quasi-star population. Their short predicted lifetimes (tens of Myr), coupled with the high observed comoving density of LRDs, suggest that most or all supermassive black holes go through a quasi-star/LRD phase during their formation and growth.