White Dwarfs as Probes of the Evolution of Planets, Stars, the Milky Way and the Expanding Universe

Coordinators: Boris Gaensicke, Matthias Schreiber, Ken Shen, and Silvia Toonen

Scientific Advisors: Alejandra Romero

As the progeny of stars born with less than ten solar masses, white dwarfs play a central role in many areas of astrophysics, ranging from exo-planets to thermonuclear supernovae. Understanding white dwarf structure and evolution requires detailed input physics, and the accuracy with which white dwarfs can be modelled directly impacts their application and utility across other fields. This program will bring together scientists developing the relevant fundamental physics, and astronomers focusing on the study of white dwarfs per se, or using them as astrophysical probes across a variety of other fields. The goal of this program is to enhance the communication between these communities, to explore novel uses of white dwarfs as astrophysical probes, and to identify current limitations and pathways to overcome them.

This program is motivated by the recent observational insights concerning white dwarfs as individuals and as a population, based on the astrometry from Gaia and large photometric (Kepler, TESS, ZTF, VeraRubin) and spectroscopic (SDSS-V, DESI, WEAVE, 4MOST) surveys. Some of the questions that these data, combined with improved input physics and white dwarf models, will answer are: How does crystallization affect white dwarf cooling? How good is our understanding of convection, overshoot, and mixing in general? How good are the predictions of the low-frequency gravitational wave foreground and thermonuclear supernovae rates (SN Ia, Iax, Ca transients)? What is the nature of the recently discovered stellar remnants of thermonuclear supernova and/or their donors? What are the architectures of planetary systems that survive the metamorphosis of their host stars into white dwarfs, and what is their ultimate fate?