Anna Francesca Pala, ESO European Southern Obeservatory, Garching — October 19, 2026

Accreting white dwarfs are close interacting stellar binaries in which matter from a low-mass star is transferred onto a white dwarf. These systems provide an ideal laboratory for testing the models of binary evolution, as they are numerous, relatively bright, and structurally simple. Nonetheless, several key scientific questions remain wide
open: the interplay between the mechanisms of angular momentum loss that drive binary evolution across different orbital period regimes is poorly understood; the evolutionary path towards the most compact systems is unknown; the intimate connection between accreting white dwarfs and Type Ia supernovae, and which pathways lead to a successful explosion, remain elusive. Answering these questions is critical to advancing our understanding of more complex systems, such as black hole and neutron star binaries, and SN Ia progenitors.
In this talk, I will present the results from a large Treasury programme with the Hubble Space Telescope. Using 132 spacecraft orbits, these observations provide accurate temperatures, masses, accretion rates and abundances for a sample of 43 accreting white dwarfs, specifically selected to pinpoint the parameter regimes in which our understanding of compact binary evolution fails most dramatically. These results offer, for the first time, full insight into the evolution of these binaries across the entire orbital period range, providing a critical test for current models of binary evolution.