http://news.xinhuanet.com/english/2007-08/29/content_6625787.htm
*Einsten right, neutron stars warp spac*
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BEIJING, Aug. 29 (Xinhuanet) -- Albert Einstein and science fiction writers
predicted the warping of space-time around neutron stars, the most dense
observable matter in the universe, and now there is proof.
The warping shows up as smeared lines of iron gas whipping around the
stars, University of Michigan and NASA astronomers say. The finding also
indicates a size limit for the celestial objects.
Study team member Sudip Bhattacharyya of NASA's Goddard Space Flight
Center said the discovery is not a total surprise, but is significant for
answering basic questions of physics.
"This is fundamental physics," Bhattacharyya explained. "There could be
exotic kinds of particles or states of matter, such as quark matter, in the
centers of neutron stars, but it's impossible to create them in the lab. The
only way to find out is to understand neutron stars."
Neutron stars can cram more than a sun's worth of material into a
city-sized sphere. A few cups of neutron-star stuff would outweigh Mount
Everest. Astronomers use these collapsed stars as natural laboratories to
study how tightly matter can be condensed under the most extreme pressures
nature can offer.
In two concurrent studies, astronomers used the European Space Agency's
XMM-Newton X-ray Observatory and the Japanese/NASA Suzaku X-ray to survey
three neutron-star binaries: Serpens X-1, GX 349+2 and 4U 1820-30. They also
studied the spectral lines from hot iron atoms that whirl around in a disk
just beyond the neutron stars' surfaces at speeds reaching 40 percent light
speed.
Normally, the measured spectral line for the superheated iron atoms
would show up as a symmetrical peak. However, their results showed a skewed
peak that was indicative of distortion due to relativistic effects. The
extremely fast motion of the gas (and the related powerful gravity), they
say, causes the line to smear, shifting it to longer wavelengths.
"We're seeing the gas whipping around just outside the neutron star's
surface," said XMM-Newton team member Edward Cackett of the University of
Michigan. "And since the inner part of the disk obviously can't orbit any
closer than the neutron star's surface, these measurements give us a maximum
size of the neutron star's diameter."
(Agencies)
Editor: Gareth Dodd
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