Speaker: Lucy McNeill (Kyoto)
Title: Tidal heating in detached double white dwarfs
Abstract:
Space based gravitational wave detectors (LISA, Taiji, TianQin) will be capable of detecting ~10-100,000 Galactic white dwarf binaries with orbital periods minutes-hours. The majority of these contain a low mass (<0.3 solar mass) Helium composition white dwarf, and these binaries will start mass transfer in k-Myr. Depending on the dynamics of the mass transfer, potential outcomes are e.g., double white dwarf merger, or stable mass transfer (where the orbital period increases).
Electromagnetic telescopes (SDSS, ZTF) have been discovering nearby (<few kpc) detached double white dwarf binaries via eclipsing for over a decade, and many of these will serve as “verification” binaries for gravitational wave detectors. Since white dwarfs have cooling timescales >Gyr, if these binaries are not exceptionally young (formation >Myr ago) it is surprising that all ~10 detected primary components in nearby binaries still have hot surface temperatures (>20,000K) and large radii (>twice the degenerate mass-radius relation).
In this talk I will show that this observed population is likely representative of the intrinsic Milky Way double white dwarf population, and can be explained with tidal heating in the (larger) Helium composition component. If white dwarfs are typically hot and large at the onset of mass transfer, then the frequency distribution of the Galactic white dwarf binary population found by gravitational wave detectors should be affected by mass transfer stability at frequencies as low as around 2mHz.