Gravitational wave generation from dynamical shape transition of protoneutron stars

TL;DR

This paper models newborn pulsars as rotating spheroids to study how neutrino escape induces shape transitions, leading to gravitational wave emission, with specific conditions identified for such transitions.

Contribution

It introduces a dynamical model of protoneutron stars as rotating spheroids that predicts shape transitions and gravitational wave generation based on initial angular momentum and eccentricity.

Findings

Shape transition occurs within a narrow initial angular frequency window.

Gravitational waves are generated during the breaking of axial symmetry.

Energy and angular momentum loss are modeled consistently with the system's evolution.

Abstract

We describe the dynamical behavior of newborn pulsars modeled as homogeneous rotating spheroids. The dynamical evolution is triggered by the escape of trapped neutrinos, provided the initial equilibrium configuration. It is shown that for a given set of values of the initial angular momentum a shape transition to a triaxial ellipsoid configuration occurs. Gravitational waves are then generated by the breaking of the axial symmetry, and some aspects of their observation are discussed. We found a narrow window for the initial values of the angular frequency and the eccentricity able to enable a dynamical shape transition, with the Kepler frequency of the rotating fluid determining the upper bound of the initial angular frequency and eccentricity. The loss of energy and angular momentum carried away by the gravitational wave is treated consistently with the solution of the equations of motion, which govern the dynamical evolution of the system. The transition in the shape of the core of the pulsar is weakly dependent on the time scale of the neutrino escape.