The Last Day, Part II
 A massive cloud of gas and dust is all that remains of a once-mightly star that blew itself to bits. Astronomer Johannes Kepler noted the bright "new" star in the night sky in late 1604, so today it's known as Kepler's Supernova. The explosion blasted the star's outer layers into space at thousands of miles per second, so this bubble of gas now spans about 14 light-years -- about three times the distance from the Sun to the next closest star system. Astronomers are continuing to learn more about the final days of the stars that end their lives as supernovae. This image is a composite that combines data from three orbiting observatories. [NASA/ESA/JHU/R.Sankrit, W.Blair]
These stars are likely to end their lives with titanic explosions, called supernovae.
As the final day begins for each of these stars, their cores will be incredibly hot and dense. Carbon and oxygen will be "fusing" together to form heavier elements, like silicon.
A few hours before the explosion, the silicon will begin fusing to make iron, sealing the star's fate. The iron won't fuse to make heavier elements, so it won't produce energy. And without energy, there's nothing to fight the star's gravity. So in a fraction of a second, the core will collapse from about the size of Earth, to the size of a city.
In most cases, this creates a superdense neutron star. The neutron star spins rapidly, generating a strong magnetic field; more about that tomorrow.
The collapse also produces a torrent of particles, which race through the star's outer layers. In a few milliseconds, the outer layers fall toward the core, then rebound violently, creating a shock wave. All of this happens in about a second, and sets up the star's final act. The shock wave races through its outer layers at thousands of miles a second. In just a few hours, that'll blast the star to bits, creating one of the brightest objects in the universe: a supernova.
Script by Damond Benningfield, Copyright 2005
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