Twist and shout: Gravitomagnetic tidal resonances in binary inspirals

Abstract

I know, the second part of the title sounds intimidating. Perhaps you're already thinking: this talk is not for me. But resist and come anyway! I promise that I will make the subject accessible to all, and that the physics is actually pretty exciting. What is it about? The context for the talk comes from the ongoing effort to measure gravitational waves from coalescing compact binaries, and to use these observations to learn something about the intimate nature of black holes and neutron stars. Black holes have no internal structure and are therefore boring, but neutron stars are deeply mysterious, featuring matter at densities that far exceed what can be found in ordinary nuclear matter in laboratories. A key to an understanding of their interior comes from the tidal deformation of each neutron star when the binary system is approaching merger, and its imprint on the emitted gravitational waves. I shall describe a less familiar type of tidal field predicted by general relativity, associated with the gravity produced by mass currents (gravitomagnetism). I will show how this tidal field can excite modes of vibration of a rotating neutron star (inertial modes) and produce resonances. The resonances have a large impact on the binary's orbital motion, and this can be measured in the emitted gravitational waves, giving us a new handle on the intimate nature of neutron stars.