Probing the effect of tides in outspiralling double white dwarf binaries with LISA

Compact object binaries including a white dwarf are unique among gravitational-wave sources because their evolution is governed not just by general relativity, but also by mass transfer and tides. While the black hole and neutron star binaries observed with ground-based gravitational-wave detectors are driven to inspiral due to the emission of gravitational radiation—manifesting as a “chirp”-like gravitational-wave signal—the astrophysical processes at work in double white dwarf (DWD) systems can cause the inspiral to stall and even reverse into an outspiral. The dynamics of the DWD outspiral thus encodes information about tides, which tell us about the behaviour of electron-degenerate matter. In this talk, I will show that the strength of tidal coupling leaves a unique signature in the distribution of gravitational-wave frequencies and frequency derivatives for the population of mass-transferring DWD systems resolvable with the Laser Interferometer Space Antenna (LISA). I will demonstrate how this effect can be directly measured using a simulated population study.