Merging White Dwarfs as Laboratories for Magnetism and Binary Evolution

Objetivo

Compact white dwarf binaries and their final outcome, the merger of the two white dwarfs, represent one of the most phenomenologically rich phases of binary evolution. They give rise to some of the most magnetic stars in the Galaxy and are leading candidates for the progenitors of Type Ia supernovae and low-frequency gravitational-wave sources. Until about a decade ago, however, only a handful of highly magnetized and rapidly rotating white dwarfs were known to be the remnants of such mergers. The advent of Gaia and modern wide-field time-domain surveys has radically transformed this picture, revealing dozens of merger candidates with extraordinary properties. The unprecedented wealth of new observations now makes it possible to move beyond individual discoveries toward the first systematic, population-level study of white dwarf merger remnants.
The MERGERS project will create the first comprehensive census of merger remnants in the Galaxy. We will combine searches in current and upcoming time-domain surveys with detailed follow-up to identify and characterize hundreds of systems. Their physical parameters and magnetic field topologies will be modeled using state-of-the-art atmosphere codes and 3D magnetohydrodynamic simulations, linking the observed diversity of remnants to their binary progenitors. From their space density, we will derive the Galactic rate of double white dwarf mergers, constraining their contribution to the Type Ia supernova rate and the population of compact binaries soon to be detected by LISA. Beyond population studies, MERGERS will use merger remnants as laboratories to study the amplification and evolution of magnetic fields, the late stages of binary interaction, and the physics of common-envelope ejection. MERGERS is uniquely timed to exploit the convergence of powerful new surveys and mature theoretical tools, transforming an emerging field into a coherent understanding of the role white dwarf mergers play in stellar and binary evolution.