Continuous Electromagnetic and Gravitational Radiation From Triaxially-Deformed, Freely-Precessing Neutron Stars

Artist’s rendition of a binary neutron star merger.
Credit: National Science Foundation/LIGO/Sonoma State University/A. Simonnet

Rapidly rotating, asymmetric neutron stars that undergo free precession can produce both modulated pulse signals and continuous gravitational radiation with characteristic features, and thus are potential interesting multi-messenger astrophysical sources.

Studies have been carried out to characterize the electromagnetic and gravitational-wave signals from freely-precessing neutron stars, mostly focused on biaxial stars; however, in the most generic cases, triaxially-deformed neutron stars demonstrate more complex features as a result of free precession. In this study, co-authored by OzGrav Associate Investigator Lilli Sun from Australian National University (who was working with Caltech at the time of this research), scientists extend previous work and derive the dynamical evolution of a generic, triaxially-deformed, freely-precessing neutron star with both analytical and numerical approaches.

If the neutron star is observed as a pulsar via radio and/or X-ray telescopes, the free precession could introduce observable characteristic modulations in both the timing and width of the pulse signals, depending on the wobble angle and other source properties. Moreover, free precession of a triaxially-deformed neutron star could manifest as additional lines in the spectra of continuous gravitational waves, detectable by the ground-based gravitational-wave detectors like Advanced LIGO, Virgo, and KAGRA.

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