Horizontal spreading of planetary debris accreted by white dwarfs. - Cunningham, Tim; Tremblay, Pier-Emmanuel; Bauer, Evan B; Toloza, Odette; Cukanovaite, Elena; Koester, Detlev; Farihi, Jay; Freytag, Bernd; Gänsicke, Boris T; Ludwig, Hans-Günter; Veras, Dimitri (Monthly Notices of the Royal Astronomical Society, 2021)