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Angular momentum sufficiency of collapsar progenitors to form massive, large-radius disks

Ascertain whether stripped progenitor stars of collapsars can retain sufficient angular momentum at core collapse to form massive (≳1 solar mass) accretion disks at large radii (≳100 gravitational radii, Rg = GM•/c^2) around the central black hole.

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Background

The proposed formation channel for sub-solar mass neutron stars relies on collapsar disks that are both massive and extend to large radii (≳100 Rg), conditions that depend critically on the angular momentum content of the progenitor star at collapse.

Whether such angular momentum distributions occur in stripped-envelope progenitors is identified as an explicit uncertainty affecting the feasibility of the overall scenario.

References

Although our estimates paint a plausible story, a number of uncertainties remain, particularly with regards to: (a) whether the stripped progenitor stars of collapsars can possess sufficient angular momentum to create massive ≳ M ⊙ disks at large radii ≳ 100 R g around the central black hole; (b) whether the criterion for forming gravitationally-bound objects is in fact satisfied by a combination of neutrino and alpha particle dissociation cooling in a full multi-dimensional turbulent disk environment; (c) the resulting mass spectrum of the bound clumps, and whether clump-fissioning or gas-aided capture leads to binary NS formation; (d) the evolution of the disk electron fraction due to pair captures prior and during gravitational collapse, and how this impacts the masses of the NSs that form; (e) feedback effects on the disk mass and energy budget from accretion onto the collapsed remnants.

— Fragmentation in Gravitationally-Unstable Collapsar Disks and Sub-Solar Neutron Star Mergers (2407.07955 - Metzger et al., 10 Jul 2024) in Section 3, Summary