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This illustration shows the alien planet around pulsar PSR J1719-1438, where ultra-high pressures caused carbon to crystallize in the remnant of a dead star. The planet is made of diamond and orbits a dense pulsing star with a radius smaller than that of our sun. CREDIT: Swinburne Astronomy Productions



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From the ashes of a supernova

Known as PSR J1719-1438, this particular pulsar completes more than 10,000 rotations in a minute. Tiny and compact, it's only about 12 miles (20 kilometers) across, but it has a mass that is 1.4 times that of our sun.

PSR J1719-1438 transformed from an average star to a radio pulsar when a dying star in a binary system exploded. The compact core of the star formed with a very high rotation speed from the ashes of the supernova.

When the second star in the system reached the end of its life, it expanded as a red giant and finally morphed into a white dwarf. The pulsar began to suck mass off its companion, causing the pulsarto spin faster and faster until it attained its breakneck speed.

From dying star to diamond planet

What happened next depends on the system. Most white dwarfs continue to orbit the new millisecond pulsar, but some are consumed by it.

"The fate depends upon the mass of the white dwarf and how far it is from the pulsar," Bailes said.

If it is both close and massive, the two spiral together. Astronomers assume this is what happened to the 30 percent of millisecond pulsars found without a companion.

In the case of the diamond planet, astronomers think that the core of the white dwarf failed to merge completely with its companion.

"When they got very close, the star lost a lot of its matter and moved out to its safe distance of about a solar radius," Bailes said.

Now tiny, having lost more than 99.9 percent of its original mass and no longer engaged in the fusion reactions that drive a star, the dead core is classified as a planet.

Ironically, the star-turned-planet is larger than its sun. With a diameter of about 37,300 miles (60,000 km), it's five times the size of Earth, but 3,000 times larger than the millisecond pulsar it orbits.

The planet itself orbits the pulsar in a little more than two hours. The entire system would fit within the diameter of our sun.

The research was published online in the Aug. 25 edition of the journal Science. -- http://news.yahoo.com/

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