What can be learned from a proto-neutron star's mass and radius?

TL;DR

This study uses numerical simulations to analyze proto-neutron star masses and radii shortly after birth, revealing limitations in extracting nuclear equation of state information from early observations.

Contribution

It demonstrates that early measurements of proto-neutron star properties do not constrain the cold neutron star equation of state due to the hot, non-beta-equilibrated state.

Findings

Mass and radius measurements within the first second are insufficient to determine the cold neutron star EoS.

Proto-neutron star properties are highly sensitive to initial conditions and neutrino cooling.

Early observations cannot reliably inform about the nuclear matter properties at cold, beta-equilibrated conditions.

Abstract

We make extensive numerical studies of masses and radii of proto-neutron stars during the first second after their birth in core-collapse supernova events. We use a quasi-static approach for the computation of proto-neutron star structure, built on parameterized entropy and electron fraction profiles, that are then evolved with neutrino cooling processes. We vary the equation of state of nuclear matter, the proto-neutron star mass and the parameters of the initial profiles, to take into account our ignorance of the supernova progenitor properties. We show that if masses and radii of a proto-neutron star can be determined in the first second after the birth, e.g. from gravitational wave emission, no information could be obtained on the corresponding cold neutron star and therefore on the cold nuclear equation of state. Similarly, it seems unlikely that any property of the proto-neutron star equation of state (hot and not beta-equilibrated) could be determined either, mostly due to the lack of information on the entropy, or equivalently temperature, distribution in such objects.