August 25, 2011
Astronomers have discovered the densest extrasolar planet yet: A Jupiter-mass remnant of a carbon- and oxygen-rich star that measures no more than 55,000 km (31,000 mi.) across. The odd world, whose density is on average at least 23 g/cm³ (0.80 lb/in³) -- or about twice that of lead -- is probably crystalline and possibly largely composed of ultradense diamond.
The planet orbits its parent sun—a pulsar, or a rapidly-spinning neutron star that emits an intense beam of radio waves, dubbed PSR J1719-1438—once every 2 hours and 10 minutes, the researchers reported online on August 25, 2011 in Science. The planet's orbit measures about 600,000 km (373,000 mi.) across, only 50% more than the average distance from Earth to the moon.
How such a dense planet formed is unclear, the researchers say, but it's probably the crystalline vestige of a white dwarf star whose atmosphere was stripped away by the parent pulsar. Most of the pulsars that spin faster than once per 20 milliseconds are part of a binary star system, but about 30% have no companions whatsoever, the scientists note. Only one other rapidly-spinning pulsar is known to be orbited by Earth-mass planets—a sign that exotic planets such as this megadiamond are, like their Earthly counterparts, rare indeed.
credit: Swinburne Astronomy Productions (animation); AAAS (text)
source: http://astronomy.swin.edu.au/production/pulsar/
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