Formation of Massive Black Holes in Rapidly Growing Pre-Galactic Gas Clouds

Wise, J., Regan, J., O’Shea, B., Norman, M., Downes, T., & Xu, H., 2019, Nature, Volume 566, Issue 7742, p.85-88.

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Summary

Abstract

Wise and collaborators use the Renaissance Simulations to study how massive black-hole seeds could form in the early universe. They find two metal-free halos that grow rapidly while receiving a moderate amount of Lyman-Werner radiation from nearby galaxies. Rapid halo growth heats the gas and delays normal Population III star formation until large amounts of gas collapse at rates high enough to form supermassive stars and, later, direct-collapse black holes.

Background and Main Question

  • The billion-solar-mass black holes observed in the early universe likely required large seed black holes that formed very quickly.
  • One possible pathway begins with a supermassive star containing roughly 10,000 solar masses, which later collapses into a black hole.
  • Earlier models usually required very strong Lyman-Werner radiation to prevent ordinary Population III star formation.

Simulation and Halo Selection

  • The authors searched the densest Renaissance Simulation region for atomic-cooling halos that remained metal-free and had not previously formed stars.
  • Ten candidates were found among 670 atomic-cooling halos, and the most massive halo and the most strongly irradiated halo were resimulated at higher resolution.
  • Both candidates formed about 10–25 kiloparsecs from a group of young galaxies and received a Lyman-Werner intensity of about 3 J21.

Rapid Halo Growth

  • Both halos experienced periods of fast growth caused by mergers and the movement of matter along nearby filaments.
  • This growth produced dynamical heating that worked with Lyman-Werner radiation to delay gas cooling and Population III star formation.
  • The halos therefore remained metal-free until they crossed the atomic cooling limit and began collapsing.

Collapse and Supermassive-Star Formation

  • The two halos formed unstable gas cores containing tens to hundreds of thousands of solar masses.
  • Gas flowed toward the cores at rates of approximately 0.17 and 2.1 solar masses per year, above the rate needed to form a supermassive star.
  • The authors predict that the resulting stars could leave direct-collapse black-hole seeds of at least 1,000 and possibly 10,000 solar masses.

Main Conclusions

  • Rapid halo assembly may be more important for massive black-hole formation than reaching one specific critical Lyman-Werner intensity.
  • This pathway could make direct-collapse black holes more common in overdense regions than earlier estimates suggested.
  • These seeds may later appear as faint quasars that can be studied with the James Webb Space Telescope.

Best Figures

Figure 2
Mass growth and Lyman-Werner radiation histories of the two candidate halos
Both candidate halos grow beyond the atomic-cooling threshold while receiving moderate Lyman-Werner radiation. The rapid growth periods help delay ordinary star formation until the halos become much more massive.
Figure 4
Gas properties and infall rates during the collapse of the candidate halos
Gas falls into the unstable cores at rates above the critical value for supermassive-star formation, providing the fuel needed to create massive black-hole seeds.