Validity of idealized torus collapsar disk models and escape of neutron-rich material

Determine whether collapsar accretion disk simulations initialized as idealized, isolated hydrostatic tori accurately reproduce the behavior of accretion disks that form self-consistently during stellar collapse, and ascertain whether neutron-rich material synthesized in such self-consistent disks can overcome the ram pressure of the infalling stellar envelope to escape the star.

Background

A number of recent simulations of r-process nucleosynthesis in collapsars have modeled the accretion flow using an isolated preset torus in hydrostatic equilibrium, omitting the surrounding progenitor star. While these studies indicate that disks may become neutron-rich, their applicability to realistic collapsar conditions is uncertain because the stellar infall and black-hole-driven outflows—which can critically affect disk evolution and ejecta—are not included.

In realistic collapsars, the accretion disk forms self-consistently from the collapsing stellar envelope, and any neutron-rich ejecta must contend with the ram pressure of the continuing infall to escape. Establishing whether idealized torus models faithfully capture this behavior, and whether synthesized neutron-rich material can successfully escape the star, remains an explicit unresolved question motivating the present 3D neutrino-transport GRMHD simulations.

References

However, it remains unclear whether the behavior of these idealized tori resembles that of disks self-consistently formed during the stellar collapse and whether the neutron-rich elements can overcome the ram pressure of the infalling stellar gas and escape out of the collapsing star.

— Magnetically-Driven Neutron-Rich Ejecta Unleashed: Global 3D Neutrino-GRMHD Simulations of Collapsars Reveal the Conditions for r-process Nucleosynthesis  (2410.02852 - Issa et al., 2024) in Section 1 (Introduction)

The amount of matter that ultimately escapes the progenitor is uncertain at finite simulation time, so we bracket the explosion properties using two criteria for unbound material: the relativistic Bernoulli criterion, $\mathcal{B}>0$, and the geodesic criterion, $u_t<-1$.

— Strong Black Hole Natal Kicks in Magnetized Accretion-Powered Explosions  (2609.10694 - Li et al., 9 Sep 2026) in Section 3, immediately before Eq. (19)