Multiple mountains on a pulsar: implications for gravitational waves and the spin-down rate

TL;DR

This paper investigates how multiple crustal irregularities on pulsars affect gravitational wave emissions, considering both Brans-Dicke and general relativity, and provides realistic models for continuous wave signals.

Contribution

It introduces a model for gravitational wave emission from pulsars with multiple crustal mountains, incorporating Brans-Dicke theory and realistic mountain distributions.

Findings

Calculated strain, power, and torque for multiple mountains

Analyzed pulsar spin-down rate considering multiple irregularities

Provided limits within general relativity context

Abstract

A pulsar, i.e., a spinning neutron star, with a deformation could emit gravitational waves continuously. Such continuous waves, which have not been detected yet, will be very useful to study gravitational physics and to probe the extreme physics of neutron stars. While typically such waves from a pulsar are estimated considering an overall stellar ellipticity, there can be multiple irregularities or mountains in the stellar crust that the gravity of the star cannot smooth. In this paper, we consider this realistic situation and compute the strain, power, torque and the pulsar spin-down rate due to multiple mountains supported by the stellar crust. Here, we consider astronomically motivated mountain distributions and use the Brans-Dicke theory of gravity which has three polarization states: two tensors dominated by the time-varying quadrupole moment and one scalar dominated by the time-varying dipole moment. We also give the limiting results for general relativity.