We have increased the number of known white dwarfs by an order of magnitude. In a major team effort we have identified 350,000 white dwarfs among the 1.5 billion objects released by the Gaia mission in April 2018. Our published white dwarf catalogue derived from this enormous sample forms the base of our involvement in the forthcoming large spectroscopic surveys (4MOST, WAVE, DESI, SDSS-V) over the next decade, and has become a standard reference in the research area with hundreds of citations. Along the way we have also quantified data quality and the accuracy of current white dwarf models.
More than 300 simulations of white dwarf atmospheres in three-dimensions were calculated, enhancing by a factor of nearly ten the number of such realistic calculations. Most of our simulations have been focused on helium atmosphere and magnetic white dwarfs, which were modeled in 3D for the first time. Our set of accurate theoretical tools vastly improve the framework to analyse most of the 350,000 white dwarfs detected from Gaia. We have derived precise and accurate white dwarf parameters (mass, temperature, age) by combining our models, Gaia data, and external independent spectroscopic observations. This has resulted in many unexpected discoveries, including the first direct evidence of the core crystallisation of white dwarfs, a chemical phase transition of the carbon-oxygen interior from liquid to solid that was predicted 50 years ago but never observed. This has set the stage for a number of external follow-up publications on the evolution of white dwarfs and dense plasma physics. We have also discovered the closest double white dwarf merger product, an important system to quantify how stars merge and create supernovae explosions visible at distant cosmic scales.
A significant fraction of white dwarfs are hosts to evolved planetary systems, and many of them are currently accreting disrupted minor planets. These systems inform us of the fate of planetary systems and provide accurate insight into the bulk rocky composition of exo-planetary systems that is otherwise inaccessible. We have directly simulated in 3D some of these accretion events, and found that the mass of the accreted material could be orders of magnitude larger than previously thought, suggesting that some white dwarfs could have had a meal of moon-sized planets. This behaviour is due to the previously unexplored concept of convective overshoot in deep white dwarf layers, a phenomenon also important to understand nuclear burning, pulsations and chemical mixing in Sun-like stars. This opens new avenues of research following this action.
