Nonlinear dynamics of oscillating neutron stars in scalar-tensor gravity

TL;DR

This paper uses numerical simulations to study the oscillation spectra of neutron stars in scalar-tensor gravity, revealing unique nonlinear features and comparing them with linear theory to aid gravitational wave detection efforts.

Contribution

It provides the first detailed nonlinear analysis of neutron star oscillations in scalar-tensor theories, highlighting differences from general relativity and implications for gravitational wave signals.

Findings

Distinct nonlinear pulsation features for different scalar coupling strengths

Comparison between nonlinear simulations and linear perturbation predictions

Insights into gravitational wave signatures from oscillating neutron stars in alternative gravity theories

Abstract

The spectrum of oscillating compact objects can be considerably altered in alternative theories of gravity. In particular, it may be enriched by modes with no counterpart in general relativity, tied to the dynamics of additional degrees of freedom generically present in these theories. Detection of these modes, e.g. in the gravitational-wave signal from a binary compact object coalescence, could provide a powerful tool to probe the underlying theory of gravity. To access the potential of such a detection, it is crucial to understand the linear and nonlinear spectral features of dynamically formed, oscillating compact objects in alternative theories of gravity. As a step towards that goal, in this work we present a suite of 1+1 numerical relativity simulations of neutron stars in scalar-tensor theories, we carefully analyze the spectrum of stellar pulsations, and we compare results with expectations from linear perturbation theory. This allows us to build intuition for the case of binary neutron star mergers. Additionally, the models investigated in this work are representatives of two broad classes, in which the scalar field couples either strongly or weakly with the fluid. The distinct phenomenology of the nonlinear dynamics that we identify for each class of models, may find counterparts also in other alternative theories of gravity.