Gravitational Radiation from Rotational Instabilities in Compact Stellar Cores with Stiff Equations of State

TL;DR

This paper uses 3-D simulations to study gravitational waves emitted by rapidly rotating stellar cores with different stiffness levels, revealing how the instability and resulting wave signals depend on the star's properties.

Contribution

It presents the first detailed 3-D numerical analysis of rotational instabilities in polytropic stellar cores with varying stiffness, including gravitational wave predictions.

Findings

Longer gravitational wave signals for stiffer models.

Successive core recontraction and spiral arm ejection episodes.

Gravitational radiation amplitudes and frequencies depend on stellar radius.

Abstract

We carry out 3-D numerical simulations of the dynamical instability in rapidly rotating stars initially modeled as polytropes with n = 1.5, 1.0, and 0.5. The calculations are done with a SPH code using Newtonian gravity, and the gravitational radiation is calculated in the quadrupole limit. All models develop the global m=2 bar mode, with mass and angular momentum being shed from the ends of the bar in two trailing spiral arms. The models then undergo successive episodes of core recontraction and spiral arm ejection, with the number of these episodes increasing as n decreases: this results in longer-lived gravitational wave signals for stiffer models. This instability may operate in a stellar core that has expended its nuclear fuel and is prevented from further collapse due to centrifugal forces. The actual values of the gravitational radiation amplitudes and frequencies depend sensitively on the radius of the star R_{eq} at which the instability develops.