This flare-up turned out to be a nova, designated Nova Sagittarii 2012. This is the violent
expulsion of material and radiation from a re-igniting
white dwarf star. Unlike a supernova, which is the cataclysmic collapse and explosion of a massive star whose core cannot fuse anymore material, a nova is the result of material falling onto the surface of a white dwarf that’s part of a binary pair. The material, typically hydrogen and helium gas, is drawn off the white dwarf’s partner which has expanded into a red giant.
Eventually the white dwarf cannot contain all of the material that it has sucked in from its neighbor. This material is heated to tremendous temperatures on its surface as it gets compressed further and further by the white dwarf’s incredibly strong gravity. Fusion occurs on the white dwarf’s outermost layers, blasting its surface out into space in an explosion of light and energy. Nova Sagittarii 2012 as seen from the US NRL's SECCHI HI-1 instrument on the NASA STEREO-B spacecraft. The movie runs from April 20 - 24, 2012, with approximately one frame per hour.
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