Neutrino gravitational redshift and the electron fraction above nascent neutron stars
Published Web Locationhttps://doi.org/10.1016/0375-9474(96)00268-0
Neutrinos emitted from near the surface of the hot proto-neutron star produced by a supernova explosion may be subject to significant gravitational redshift at late times. Electron antineutrinos (ν̄e) decouple deeper in the gravitational potential well of the neutron star than do the electron neutrinos (νe), so that the ν̄e experience a larger redshift effect than do the νe. We show how this differential redshift can increase the electron fraction Ye in the neutrino-heated ejecta from the neutron star. Any r-process nucleosynthesis originating in the neutrino-heated ejecta would require a low Ye, implying that the differential redshift effect cannot be too large. In turn, this effect may allow nucleosynthesis to probe the nuclear equation of state parameters which set the neutron star radius and surface density scale height at times of order tph ≈ 10s to 25s after core bounce.