Prospects of observing continuous gravitational waves from known pulsars

TL;DR

This paper assesses the potential for future gravitational wave detectors to observe continuous waves from known pulsars, considering their physical properties and the limitations of current detection methods.

Contribution

It provides a detailed analysis of the detectability of gravitational waves from known pulsars with upcoming detectors, accounting for various stellar equations of state and internal magnetic fields.

Findings

Detection prospects depend on the star's equation of state and quadrupole moment.

Future detectors could observe gravitational waves from some pulsars if they have sufficiently large ellipticities.

Constraints on internal magnetic fields can be derived from non-detections.

Abstract

Several past searches for gravitational waves from a selection of known pulsars have been performed with data from the science runs of the Laser Inferometer Gravitational-wave Observatory (LIGO) gravitational wave detectors. So far these have lead to no detection, but upper limits on the gravitational wave amplitudes have been set. Here we study our intrinsic ability to detect, and estimate the gravitational wave amplitude for non-accreting pulsars. Using spin-down limits on emission as a guide we examine amplitudes that would be required to observe known pulsars with future detectors (Advanced LIGO, Advanced Virgo and the Einstein Telescope), assuming that they are triaxial stars emitting at precisely twice the known rotation frequency. Maximum allowed amplitudes depend on the stars' equation of state (e.g. a normal neutron star, a quark star, a hybrid star) and the theoretical mass quadrupoles that they can sustain. We study what range of quadrupoles, and therefore equations of state, would be consistent with being able to detect these sources. For globular cluster pulsars, with spin-downs masked by accelerations within the cluster, we examine what spin-down values gravitational wave observations would be able to set. For all pulsars we also alternatively examine what internal magnetic fields they would need to sustain observable ellipticities.