Remnant planetary systems around massive white dwarfs ($M_{\rm WD} > 0.8\,{\rm M}_\odot$) are intrinsically rare and remain poorly characterized. As the evolutionary endpoints of intermediate-mass B- ...

A population of anomalous ultra-massive white dwarfs discovered with Gaia, often referred to as the Q branch, show high (multi-Gyr) cooling delays produced by exotic physical mechanisms. They are beli...