A supernova is one of the universe's most awesome, violent events. In most cases, a supernova explosion can outshine an entire galaxy. Such catastrophic detonations leave behind spectacular legacies seen through telescopes-the Crab Nebula, as one example, is a rapidly expanding shell of beautiful, incandescent gas created by a 1054 A.D. supernova explosion. At the center of the nebula is a rapidly spinning neutron star-all that remains of a red supergiant star that once existed there.
When a massive, old star has gobbled up all of its hydrogen fuel, a new thermonuclear process begins at its core-the remaining helium and carbon then serves as the star's new fuel. With the hydrogen gone, the laws of physics seek to counterbalance an inward pull resulting from the star's heavy outer mass. However, this counterbalancing act can never be pulled off; gravity inevitably causes the core to collapse.
At the final moment of a collapsing core, a massive explosion occurs-this is called a supernova. As the explosion unfolds, plasma-ultra hot gas-is blasted far into space. For a brief moment, lasting hours or days, the supernova will outshine all the stars of its resident galaxy. As the explosion fades, the star remnant dims with only its core remaining. The remaining core is called a neutron star because it is composed entirely of densely packed neutron particles.
In some cases, supernova compression will continue past the neutron star stage and create a black hole where not even photons (light) can escape due to the extreme gravitational force of the "hole".
There are two types of supernova explosions, types I and II.
In a type-I supernova, two stars are involved. In a binary system, the larger companion star swells to a red giant, expanding dangerously close to its smaller partner. The smaller, but now more massive companion sucks gases off the red giant until what remains of the giant is a white dwarf star. In reverse roles, the companion now swells to a red giant and the dwarf sucks gases off its newly bloated companion. Finally, when all gaseous material is stripped away, two white dwarfs remain. But the odd dance of death is not yet complete. The two dwarf stars fall in toward each other and explode. According to most astronomers, type-I supernova explosions leave nothing behind.
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.