The Growth of Black Holes from Population III Remnants in the Renaissance Simulations

Summary

Abstract

Smith and collaborators use the Renaissance Simulations to study the growth of more than 15,000 black holes left behind by Population III stars. Most of these black holes gain almost no mass because they rarely encounter cold, dense gas for long enough to grow. Star formation and stellar feedback consume or disperse the available gas, making it difficult for these early black holes to become intermediate-mass or supermassive black holes.

1. Introduction

• Black holes left by Population III stars are possible seeds of the supermassive black holes observed in the early universe.
• Earlier studies found that radiation and supernovae remove gas from young halos, leaving many of these black holes “born starving.”
• This paper tests whether mergers and later halo growth eventually place the black holes in environments where they can accrete efficiently.

2. Simulation Suites

• The study follows roughly 15,000 Population III remnants in the Renaissance Simulations across dense, average, and underdense regions.
• A smaller, higher-resolution Pop2Prime simulation is used to examine individual black holes and the effect of turning off star formation.
• Together, the simulations cover halos from approximately 10⁶ to 10⁹ solar masses.

3. Analysis

• The authors estimate each remnant’s initial black-hole mass from the mass and final state of its Population III progenitor.
• Black-hole growth is calculated afterward using the local gas density, temperature, and relative velocity recorded in the simulations.
• The model allows super-Eddington accretion, although such events turn out to be extremely rare and brief.

4. Results

• Most black holes gain a negligible amount of mass, and fewer than 100 out of approximately 15,000 grow by more than 0.1 percent.
• Only one black hole briefly exceeds the Eddington accretion rate, and growth shows no clear dependence on host-halo mass.
• Dense gas clumps could support faster growth, but black holes are usually far from them and stellar feedback destroys the clumps quickly.

5. Summary and Discussion

• Population III remnants generally do not experience the sustained accretion needed to become massive black-hole seeds during this period.
• When star formation is turned off, gas can rebuild around the black holes and their average growth rate rises substantially.
• Significant growth may therefore have to wait for later times, more massive halos, or environments where stellar feedback is less effective.

Best Figures

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