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White Dwarfs III
A white-dwarf star system has undergone a traumatic experience. The original star has swelled up, incinerating nearby planets and asteroids, then flung its outer layers into space, making the orbits of surviving planets unstable. All that remains of the star is a tiny, dense core — a faint cosmic cinder known as a white dwarf.
Yet the trauma for such a system may not end there. Observations in the last few years have shown that some white dwarfs may pulverize some of their remaining planets or asteroids and gobble up their remains.
One such white dwarf is known as GD 362. It’s about 165 light-years away, and it’s about three-quarters as massive as the Sun.
The surface gravity of such a white dwarf is so strong that heavy elements quickly sink from sight, leaving lightweight hydrogen and helium in a thin outer layer.
But astronomers have detected lots of heavy elements in the outer layer of GD 362 — elements like those found in Earth and the Moon. And a thick ring of dust encircles the dead star.
It’s possible that a large asteroid wandered too close and was torn apart by the white dwarf’s gravity. The debris formed a ring, which is dumping material onto the star. But GD 362 has been a white dwarf for so long that few asteroids should come that close. That could mean that the disk has been there for billions of years. If so, then it could be the remains not of an asteroid, but of a planet larger than Earth — a planet disrupted by a dying star.
Script by Damond Benningfield, Copyright 2011
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