Quark deconfinement as a natural trigger of Type-I critical collapse: black holes from neutron stars deemed stable

Spherically symmetric general-relativistic simulations show that a first-order hadron--quark phase transition can collapse radially stable neutron stars into black holes, even when a stable hybrid star of the same baryon mass exists. The dynamical threshold lies $0.12\,M_\odot$ in baryon mass below the static one, so black holes can be lighter than the heaviest stable star. The threshold is a Type-I critical point: near it, the star lingers at an unstable hybrid star of equal baryon mass for a time set by that star's unstable mode. The effect persists within a narrower window for finite conversion rates.