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A star system in the constellation Ophiuchus, which is in the east on June evenings, can’t keep quiet. It pops off every decade or two. In just a day, it grows tens of thousands of times brighter. But those outbursts may be only the prelude to a bigger one: The star may blast itself to bits as a supernova.
RS Ophiuchi is a binary — two stars locked in a mutual orbit. One of the stars is a white dwarf — the corpse of a star that was once like the Sun. The other star is a red giant — a star near the end of its own lifetime. It’s puffed itself up so that it’s much bigger and brighter than the Sun.
The stars are so close together that the white dwarf “steals” gas from the red giant. The gas forms a disk around the white dwarf before it spirals onto the dead star. The white dwarf’s gravity squeezes this new layer of gas. Material at the bottom of that layer gets so hot that it triggers a nuclear explosion. That blows some of the top layer into space, causing the system to flare up. The last outburst appeared in 2006, with RS Ophiuchi getting bright enough to see with the unaided eye.
Not all of the gas is blown away — some of it builds up. But if the white dwarf reaches about 1.4 times the mass of the Sun, a chain reaction will blow it apart. And RS Ophiuchi is nearing that limit. So someday, it probably will destroy itself as a supernova — the final outburst of a star that can’t keep quiet.
More about Ophiuchus tomorrow.
Script by Damond Benningfield