Speaker
Description
We identify a previously unrecognized spin–orbit resonance that can naturally arise in neutron star binaries. This resonance provides a new and direct probe of neutron star ellipticity, enabled by finite stellar quadrupole moments such as those produced by strong internal magnetic fields. We show that the resonance produces a distinctive and measurable gravitational-wave phase shift, allowing precise measurement of the neutron star’s ellipticity and moment of inertia.
We further conduct the first ellipticity search across the entire gravitational-wave catalog up to O4a, finding no detections but establishing the framework for future constraints. We demonstrate that detecting this resonance would have significant implications for both astrophysics and fundamental physics, including the internal structure of neutron stars, the prevalence of magnetars in binaries, and tests of strong-field gravity.