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EX Hydrae

December 19, 2013

Just because a star is small doesn’t mean it’s boring. In fact, two tiny stars in the constellation Hydra are among the most active in our region of the galaxy. One of the stars takes hot gas from the other, which triggers occasional outbursts.

EX Hydrae is about 200 light-years away. Its main star is a white dwarf — the dead core of a once-normal star. It’s about a third as massive as the Sun, but only about as big as Earth. It’s so dense that its surface gravity is quite powerful — strong enough to pull material off the surface of its companion. That star is a red dwarf — a bare cosmic ember just one-tenth as massive as the Sun.

The stolen gas falls on the white dwarf in a couple of ways. Most of it forms a wide, thin disk around the white dwarf. The disk gets extremely hot, so it produces lots of X-rays. But the white dwarf also generates a strong magnetic field. Some of the stolen gas follows the lines of magnetic force and flows onto the star’s poles.

Every few years, so much gas piles up in the disk around the white dwarf that the disk can’t handle it. That triggers an outburst that makes the system flare about 10 times brighter than normal. It lasts only a few days before EX Hydrae returns to normal — a pair of small but busy stars.

And a team of scientists and musicians has converted data from EX Hydrae into sound — and music. We’ll have more about that tomorrow.


Script by Damond Benningfield, Copyright 2013

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