Fragmentation criterion under neutrino and alpha-particle dissociation cooling in turbulent collapsar disks

Determine whether the fragmentation criterion for forming gravitationally bound objects is satisfied in full multi-dimensional, turbulent collapsar disks when cooling arises from neutrino emission and alpha-particle dissociation.

Background

The authors posit that neutrino cooling and alpha-particle dissociation may enable gravitationally unstable collapsar disks to fragment into bound clumps, but emphasize that confirming fragmentation requires multi-dimensional turbulent disk modeling.

This uncertainty directly affects whether clumps can form and subsequently collapse to neutron stars in the proposed channel.

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