Measuring neutron-star ellipticity with measurements of the stochastic gravitational-wave background

Abstract

Galactic neutron stars are a promising source of gravitational waves in the analysis band of detectors such as LIGO and Virgo. Previous searches for gravitational waves from neutron stars have focused on the detection of individual neutron stars, which are either nearby or highly non-spherical. Here we consider the stochastic gravitational-wave signal arising from the ensemble of Galactic neutron stars. Using a population synthesis model, we estimate the single-sigma sensitivity of current and planned gravitational-wave observatories to average neutron star ellipticity $\epsilon$ as a function of the number of in-band Galactic neutron stars $N_{\text{tot}}$. For the plausible case of $N_{\text{tot}}\approx 53000$, and assuming one year of observation time with colocated initial LIGO detectors, we find it to be ${\sigma }_{\epsilon }=2.1\times 10^{-7}$, which is comparable to current bounds on some nearby neutron stars. (The current best $95\%$ upper limits are $\epsilon \lesssim 7\times 10^{-8}.$) It is unclear if Advanced LIGO can significantly improve on this sensitivity using spatially separated detectors. For the proposed Einstein Telescope, we estimate that $\sigma \epsilon =5.6\times 10^{-10}$. Finally, we show that stochastic measurements can be combined with measurements of individual neutron stars in order to estimate the number of in-band Galactic neutron stars. In this way, measurements of stochastic gravitational waves provide a complementary tool for studying Galactic neutron stars.

References in corpus (5)

• LIGO: The Laser Interferometer Gravitational-Wave Observatory
• Upper limits on gravitational wave emission from 78 radio pulsars
• Upper limit map of a background of gravitational waves
• Einstein@Home all-sky search for periodic gravitational waves in LIGO S5 data
• Population synthesis of radio and gamma-ray millisecond pulsars from the Galactic disk

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• Searching for continuous gravitational waves from highly deformed compact objects with DECIGO
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