The Pair-instability Mass Gap for Black Holes

doi:10.3847/2041-8213/abf2c4

The Pair-instability Mass Gap for Black Holes

2021-05-11

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DOI：10.3847/2041-8213/abf2c4

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Stellar evolution theory predicts a gap in the black hole birth function caused by the pair instability. Many presupernova stars that have a core mass below some limiting value, M (low), after all pulsational activity is finished, collapse to black holes, while more massive ones, up to some limiting value, M (high), explode, promptly and completely, as pair-instability supernovae. Previous work has suggested M (low) approximate to 50 M (circle dot) and M (high) approximate to 130 M (circle dot). These calculations have been challenged by recent LIGO observations that show many black holes merging with individual masses M (low) greater than or similar to 65 M (circle dot). Here we explore four factors affecting the theoretical estimates for the boundaries of this mass gap: nuclear reaction rates, evolution in detached binaries, rotation, and hyper-Eddington accretion after black hole birth. Current uncertainties in reaction rates by themselves allow M (low) to rise to 64 M (circle dot) and M (high) as large as 161 M (circle dot). Rapid rotation could further increase M (low) to similar to 70 M (circle dot), depending on the treatment of magnetic torques. Evolution in detached binaries and super-Eddington accretion can, with great uncertainty, increase M (low) still further. Dimensionless Kerr parameters close to unity are allowed for the more massive black holes produced in close binaries, though they are generally smaller.

Keywords:

GAMMA-RAY BURSTS

PRESUPERNOVA EVOLUTION

STAR PROGENITORS

HELIUM STARS

BINARY

NUCLEOSYNTHESIS

RATES

WINDS

SENSITIVITY

ROTATION

The Pair-instability Mass Gap for Black Holes

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