Student researchers from Lift Kingsley, in collaboration with Orbyts Fellow Hiba Noor from UCL Physics and Astronomy, have investigated the variability of accretion rates in white dwarfs. Using a rich dataset of multi-epoch UVES spectra from the Very Large Telescope, their research meticulously tracked changes in the metal content of these dense stellar remnants. The study’s primary objective was to observe how the calcium spectral line varied over a two-decade period, providing critical insight into the stability of debris disk accretion.

White dwarfs, the remnants of Sun-like stars, are often 'polluted' by the accretion of material from disrupted planetary bodies. A specific subclass, known as DAZ white dwarfs, is particularly sensitive to these accretion events due to their rapid metal sinking timescales. Despite this high sensitivity, a long-standing challenge in the field has been the lack of confirmed observations of variable accretion — reflecting both the lack of long-term monitoring and our limited knowledge of the mechanisms and timescales that govern how material is supplied from the debris reservoir. This research sought to close that gap by utilising an extensive historical spectral archive.

The analysis revealed that for the majority of the twenty stars in the sample, the equivalent width of the Ca II K line remained stable over the twenty-year baseline. This finding is consistent with the hypothesis of steady-state accretion from massive, long-lived debris disks. However, a discovery was made with two white dwarfs, WD 0106-328 and WD 1457-086, which showed significant decreases in their accretion rates. This is the first potential evidence of variable accretion, directly challenging the steady-state assumption often made for these objects.

This work marks a step forward in our understanding of the final stages of planetary system evolution. By confirming that accretion rates can indeed change over time, the research provides a new lens through which to view debris disk dynamics. The results call for further investigation, including the analysis of other metal lines to track changes in the composition of the accreted material and new, dedicated observations to confirm the variability in the two identified white dwarfs!