Establish the hydrogen-envelope contribution to direct-collapse black-hole masses

Determine what fraction of a progenitor’s hydrogen envelope is ultimately accreted by a directly collapsing stellar core in order to establish the resulting black-hole mass.

Background

The population-synthesis treatment assigns the mass of a direct-collapse black hole to the progenitor helium-core mass, whereas alternative prescriptions may allow part of the hydrogen envelope to collapse onto the remnant. Because this choice directly affects the predicted black-hole mass spectrum, the envelope-accretion fraction is an unresolved aspect of the supernova model.

References

The fraction of the hydrogen envelope ultimately accreted during direct collapse remains uncertain.

— A Census of Stellar-mass Black Holes in the Milky Way with POPKIN. I. Isolated Black Holes  (2609.29211 - He et al., 24 Sep 2026) in Section 2.3.3, “SN Explosion”