2019MNRAS.484L.109S

Archival data from the WISE satellite reveal infrared flux variations of tens of per cent around numerous dusty white dwarfs. Data spanning more than 7 yr reveal more than half of known systems are varying in the 3.4 µm band, while the 4.6 µm data are challenging to interpret due to lower signal-to-noise ratios. The sparsely-sampled data limit interpretation, but the heterogeneous light curves suggest each source may be idiosyncratic, where there may be competing processes operating on different time-scales. Collisions are likely driving the observed decays in flux, and this finding suggests that dust production is operating more often than indicated by previous observations. The observed variation is at odds with the canonical flat disc model in isolation, and underscores the need for infrared monitoring of these evolved planetary systems to inform the next generation of theoretical models.