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Small but Bright

June 16, 2015

Some of the brightest jewels in the universe are also some of the smallest: the exploding cores of dead stars.

A star like the Sun spends most of its time “fusing” the hydrogen fuel in its core to make helium. It then spends a shorter time fusing the helium to make carbon and oxygen. After that, it can no longer continue the process. It expels its outer layers into space, leaving behind only its dead core, known as a white dwarf. It’s about as heavy as the Sun, but only as big as Earth.

For the Sun itself, the story will end there. But if a white dwarf has a close companion, the story can continue.

If the companion is a “normal” star, the white dwarf may steal gas from its surface. If enough gas builds up on the white dwarf, it can trigger a supernova — an explosion that blasts the star to bits. And if the companion is another white dwarf, then the two stars may spiral together, again triggering a supernova.

These explosions all brighten and fade in a characteristic way. From that cycle, astronomers can deduce the supernova’s true brightness. Comparing that to how bright it looks reveals the distance to the supernova and its host galaxy.

The blasts are visible across vast distances. That makes them good tools for measuring the size of the universe and the way it’s evolving. In fact, they helped reveal that the universe is expanding faster as it ages — a discovery made possible by small but dazzling stellar jewels.

More tomorrow.


Script by Damond Benningfield, Copyright 2015


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