Evidence for a minimum ellipticity in millisecond pulsars

TL;DR

This paper presents evidence that millisecond pulsars have a minimum ellipticity around 10^{-9}, suggesting some spin-down is due to gravitational waves and implying detectable signals for current gravitational-wave detectors.

Contribution

It provides population-based evidence for a minimum ellipticity in MSPs and discusses its implications for neutron star properties and gravitational-wave detection.

Findings

MSPs have a minimum ellipticity of approximately 10^{-9}.

Some MSP spin-down is likely due to gravitational-wave emission.

Gravitational waves from MSPs could be detected by current detectors in the near future.

Abstract

Neutron stars spin down over time due to a number of energy-loss processes. We provide tantalizing population-based evidence that millisecond pulsars (MSPs) have a minimum ellipticity of $\epsilon\approx10^{-9}$ around their spin axis and that, consequently, some spin down mostly through gravitational-wave emission. We discuss the implications of such a minimum ellipticity in terms of the internal magnetic field strengths and nuclear matter composition of neutron stars and show it would result in the Advanced LIGO and Virgo gravitational-wave detectors, or their upgrades, detecting gravitational waves from some known MSPs in the near future.