Regal Explosions, Part 2

StarDate: November 6, 2009

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If a star explodes but no one sees it, did it really explode? In the case of a star in Cassiopeia, the answer is yes. But the fact that no one saw it raises some interesting questions about the star itself.

A radio telescope discovered the remains of the star back in 1947, and astronomers cataloged it as Cassiopeia A. They didn't see those remains until several years later. The remains form a bubble of hot gas that's about 10 light-years across, and expanding at the rate of 10 million miles an hour.

From the size of the bubble and the speed of its expansion, astronomers estimated that the star exploded around the year 1667 as seen from Earth. It's so close that it should have been bright enough to outshine just about everything else in the night sky. Yet there are no confirmed reports of anyone seeing the star.

The original star was probably a supergiant -- a star that's much bigger and heavier than the Sun. When it used up the nuclear fuel in its core, the core collapsed and the outer layers were blasted into space, creating a supernova -- a blast that usually shines as brightly as billions of normal stars.

So why didn't anyone see it? The answer may be that the star shed much of its outer layers of gas and dust before it exploded, surrounding itself in a cocoon. When it exploded, this cocoon absorbed most of the light. So Cassiopeia A prevented the people of Earth from seeing its violent demise.

Script by Damond Benningfield, Copyright 2009

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