Gravitational-wave asteroseismology with fundamental modes from compact binary inspirals.

Gravitational waves (GWs) from binary neutron stars encode unique information about ultra-dense matter through characterisic signatures associated with a variety of phenomena including tidal effects during the inspiral. The main tidal signature depends predominantly on the equation of state (EoS)-related tidal deformability parameter Λ, but at late times is also characterised by the frequency of the star’s fundamental oscillation mode (f-mode). In General Relativity and for nuclear matter, Λ and the f-modes are related by universal relations which may not hold for alternative theories of gravity or exotic matter. Independently measuring Λ and the f-mode frequency enables tests of gravity and the nature of compact binaries. Here we present directly measured constraints on the f-mode frequencies of the companions of GW170817. We also show that future GW detector networks will measure f-mode frequencies to within tens of Hz, enabling precision GW asteroseismology with binary inspiral signals alone. Independently measuring the tidal deformability and the fundamental oscillation mode (fmode) frequency enables tests of gravity and the nature of compact binaries. Here, the authors constrain the f-mode frequencies of the companions of GW170817 from direct measurements, demonstrating gravitational wave asteroseismology with binary inspiral signals alone.