The mass of the homologously collapsing inner core is set by an effective…

PHYSICS · Subjective · Fermi University Physics · Astrophysics & Cosmology · Stellar death and compact objects · Stellar death and compact objects

Stars from the Inside, Ch Stellar explosions: core collapse, the neutrino-driven shock, radioactive light and remnants

Problem

The mass of the homologously collapsing inner core is set by an effective Chandrasekhar-type limit built from the electron fraction

Y_e

, with

M_{\rm ic} \propto Y_e^2

(as

Y_e

plays the role of

\mu_e^{-1}

). Electron captures during infall lower

Y_e

from

0.46

, at the start of collapse, to

0.40

by the time the inner core reaches nuclear density and bounces. If the inner core mass would have been

M_{\rm ic,0} = 0.75\,M_\odot

at the initial

Y_e

, predict its mass at bounce, and state in one sentence the physical reason the mass falls.