Radial oscillations of proto-neutron stars

TL;DR

This paper studies the radial oscillations of proto-neutron stars using different equations of state, revealing how entropy, neutrino trapping, and mass influence their oscillation frequencies and stability.

Contribution

It provides the first detailed calculation of eigenfrequencies and oscillation functions of proto-neutron stars considering isentropy and fixed lepton fractions with various equations of state.

Findings

Oscillation frequencies decrease with entropy and neutrino trapping in low-mass stars.

Fundamental frequency drops to zero at maximum mass, indicating stability limits.

Different characteristics of oscillations are observed across mass regions.

Abstract

We investigate radial oscillations of proto-neutron stars, employing equations of state described by the Brueckner-Hartree-Fock theory or the relativistic mean field model, and assuming isentropy and fixed lepton fractions for the internal structure. We calculate the eigenfrequencies and corresponding oscillation functions, which show different characteristics in different mass regions. In the low-mass region around 1.4 solar mass, the radial oscillation frequencies are lowered by large entropy and neutrino trapping, along with a reduction of the average adiabatic index. In the region close to the maximum mass, the fundamental oscillation frequency drops rapidly and vanishes at the maximum mass, in accordance with the critical stability criterion $\partial M /\partial \rho_c = 0$, as for cold neutron stars.