> "Not all, but some white dwarfs transition from being hydrogen- to helium-dominated on their surface," Caiazzo explains. "We might have possibly caught one such white dwarf in the act."

Wicked cool! The article goes on to explain that it may be due to a difference in the strength of the magnetic fields on either side of the star...

I might be mis-remembering from astronomy class ( long ago now ) but I'd thought that these transitions usually happen very quickly -- it's interesting that we can just watch it go!