In a binary system with a white dwarf and a secondary star, gravity can attract material from the secondary onto the dwarf's surface.  
U Geminorum systems, with periods of 30 days, are dwarf examples of this class.  In a binary system with a white dwarf and a secondary star, gravity can attract material from the secondary onto the dwarf's surface.  Eventually the new material goes unstable, a thermonuclear explosion occurs, and the process begins anew.  For ten points, name this occurrence, similar to but less destructive than a type-1 supernova.
U Geminorum systems, with periods of 30 days, are dwarf examples of this class.  
novae (Accept dwarf novae on an incredibly early buzz.  Do not accept supernova or type-2 supernova)