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Our violent universe

A type-II supernova explosion happens when a red supergiant star, more than ten times the mass of Sun, burns up the last of its thermonuclear fuel. Since the object has nearly stopped generating nuclear energy to hold up its tremendous mass, gravity triggers a rapid collapse of the star's gaseous outer shell. As the collapse of the outer shell compresses the sun's iron core, a stream of atomic and subatomic particles blasts away the outer shell in a violent detonation and explosion.

Because our Sun lacks the mass to become a red supergiant, and because we lack a large companion star, there won't be a fatal supernova explosion. Instead, billions of years from now, when our Sun burns up the last of its hydrogen fuel, it will swell to a red giant 100 times its present size-vaporizing the inner planets, including Earth-and then fade away until it is 100 times smaller than current size. At this point, all that will remain of our familiar Sun is a cold, black mass.

What's in the Sky: During the pre-dawn hours, check out the constellation Ursa Major, aka the Big Dipper. At the end of the Dipper's handle, Mizar forms an optical "double star" with Alcor. Nearby on the sky map, in 1996, two planets were found orbiting star 47 Ursae Majoris. This Sunlike star, 46 light years distant, is visible to the naked eye. It located to the right of Canes Venatici.

Louis Varricchio. M.Sc., lives in Vermont. He was a NASA science writer. He holds undergraduate and graduate degrees in communications and space science studies.

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