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Pleiades White Dwarf

October 12, 2013

Like people, stars eventually die. They can do so in one of two ways: with a bang or with a whimper. The most massive stars die in titanic explosions. But less massive stars die gently, by casting off their outer layers. What mass marks the dividing line between the two fates? A clue comes from one of the nearest and most beautiful star clusters.

To the unaided eye, the Pleiades looks like a tiny dipper in the constellation Taurus, which rises in mid-evening and is high in the east at midnight. But a pair of binoculars transforms the cluster into a beehive of stars. The brightest of these stars — and the next to die — are blue, and weigh about six times as much as the Sun.

But the Pleiades also has a much less impressive member: a white dwarf — the leftover corpse of a star that died by gently casting its outer layers into space.

The more mass a star is born with, the sooner it dies. That means the white dwarf must be the remnant of a star that was a bit more than six times the Sun’s mass — anything less massive and it would still be shining as a “normal” star. So stars that are less than six times the mass of the Sun don’t end their lives with a bang.

Astronomers estimate that the dividing line between an explosive death and a gentle one is about eight times the mass of the Sun. The few stars that are born above that line will explode. But the rest will die gently, leaving behind a hot, dense core — like the white dwarf in the Pleiades.


Script by Ken Croswell, Copyright 2013

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