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."
Source:Xinhua/agencies
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