Inside and outside of supernovae

A newly formed neutron star in a supernova finds itself in a dense environment, in which the gravitational energy of accreting matter can be lost to neutrinos. For the conditions in SN 1987A, 0.1M may have fallen back onto the central neutron star on a timescale of hours after the explosion, after which the accretion rate is expected to drop sharply. Radiation is trapped in the flow until the mass accretion rate drops to 2×10^–4 M yr^–1 at which point radiation can begin to escape from the shocked envelope at an Eddington limit luminosity. Between this neutrino limit and the Eddington limit, 3×10^–8 M yr^–1, there are no steady, spherical solutions for neutron star accretion. SN 1987A should have reached the neutrino limit within a year of the explosion; the current lack of an Eddington luminosity can be attributed to black hole formation or to a clearing of the neutron star envelope. There is no evidence for newly formed neutron stars in supernovae. Radio supernovae, which were initially interpreted as pulsar activity, probably involve circumstellar interaction; SN 1993J shows especially good evidence for outer shock phenomena.