Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Little Red Dots As Late-stage Quasi-stars

Mitchell C. Begelman, Jason Dexter

TL;DR

This paper proposes that the James Webb Space Telescope's Little Red Dots (LRDs) are the late-stage evolution of quasi-stars—black holes embedded in massive, radiation-pressure envelopes arising from direct-collapse SMBH seed formation. Through a deductive quasi-star model, the authors show that late-stage systems with $M_{ m BH}/M_*\gtrsim 0.1$ have a two-zone structure with a saturated-convection interior and a scattering-dominated outer layer, yielding a color temperature of $T_{\rm color} \sim 6\times 10^3$ K and an effective temperature of $T_{\rm eff} \sim 3\times 10^3$ K, with radii around $R_* \sim 6\times 10^{16}$ cm and luminosities near the total-envelope Eddington limit $L_E$. The predicted spectra feature red colors, a strong Balmer break, and Balmer lines broadened by electron scattering (with $\tau_{\rm sc}\sim 2$–$40$), while X-ray emission is suppressed by the large electron column. Given lifetimes of tens of Myr and a comoving density of $\sim 10^{-5}$ cMpc$^{-3}$ at $z\sim5-6$, quasi-stars could be a ubiquitous, short-lived SMBH-seeding phase contributing significantly to the cosmic BH mass budget and influencing early galaxy formation.

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.

Little Red Dots As Late-stage Quasi-stars

TL;DR

This paper proposes that the James Webb Space Telescope's Little Red Dots (LRDs) are the late-stage evolution of quasi-stars—black holes embedded in massive, radiation-pressure envelopes arising from direct-collapse SMBH seed formation. Through a deductive quasi-star model, the authors show that late-stage systems with have a two-zone structure with a saturated-convection interior and a scattering-dominated outer layer, yielding a color temperature of K and an effective temperature of K, with radii around cm and luminosities near the total-envelope Eddington limit . The predicted spectra feature red colors, a strong Balmer break, and Balmer lines broadened by electron scattering (with –), while X-ray emission is suppressed by the large electron column. Given lifetimes of tens of Myr and a comoving density of cMpc at , quasi-stars could be a ubiquitous, short-lived SMBH-seeding phase contributing significantly to the cosmic BH mass budget and influencing early galaxy formation.

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 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 , 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.

Paper Structure

This paper contains 7 sections, 8 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Late-stage quasi-stars
  3. Internal structure
  4. Outer layers
  5. Quasi-star spectra
  6. Evolutionary Context of Quasi-stars/LRDs
  7. Discussion

Figures (1)

  • Figure 1: Schematic diagram showing proposed stages in the formation and early growth of supermassive black holes from left to right. Approximate total ($M$) and black hole ($M_{BH}$) masses, luminosities $L$, and lifetimes $T$ are very rough estimates assuming a continued infall rate of $\gtrsim 0.1 M_\odot$ yr$^{-1}$. We propose that observed little red dots correspond to late quasi-stars. Rare precursors should appear bluer in color at similar or lower luminosity.