|
XMM-Newton and Suzaku help pioneer method for probing exotic matter
August 28, 2007Astronomers using XMM-Newton and Suzaku have seen Einstein's predicted distortion of space-time and pioneered a ground-breaking technique for determining the properties of neutron stars.
ESA's XMM-Newton and the JAXA/NASA Suzaku X-ray observatories have been used to see the distortion of space-time around three neutron stars. These objects contain the densest observable matter in the Universe.
Neutron stars cram more than a Sun's worth of material into a city-sized sphere. This means that a cup of neutron-star stuff would outweigh Mount Everest. Astronomers use these collapsed stars as natural laboratories to study how tightly matter can be compacted under the most extreme pressure that nature can offer.
"This is fundamental physics," says Sudip Bhattacharyya at NASA's Goddard Space Flight Center, USA. "There could be exotic kinds of particles or states of matter, such as quark matter, in the centres of neutron stars, but it's impossible to create them in the lab. The only way to find out is to understand neutron stars."
To address this mystery, scientists must accurately and precisely measure the diameters and masses of neutron stars. In two concurrent studies, one with XMM-Newton and the other with Suzaku, astronomers have taken a big step forward.
Using XMM-Newton, Bhattacharyya and his colleague Tod Strohmayer observed a binary system known as Serpens X-1, which contains a neutron star and a stellar companion. They studied a spectral line from hot iron atoms that are whirling around in a disc, just beyond the neutron star's surface, at 40% the speed of light.
Previous X-ray observatories detected iron lines around neutron stars, but they lacked the sensitivity to measure the shapes of the lines in detail.
Thanks to XMM-Newton's large mirrors, Bhattacharyya and Strohmayer found that the iron line is broadened asymmetrically by the gas's extreme velocity, which smears and distorts the line because of the Doppler effect and beaming effects predicted by Einstein's special theory of relativity. The warping of space-time by the neutron star's powerful gravity, an effect of Einstein's general theory of relativity, shifts the neutron star's iron line to longer wavelengths.
"We have seen these asymmetric lines from many black holes, but this is the first confirmation that neutron stars can produce them as well. It shows that the way neutron stars accrete matter is not very different from that of black holes, and gives us a new tool to probe Einstein's theory," says Strohmayer.
A group led by Edward Cackett and Jon Miller of the University of Michigan, which includes Bhattacharyya and Strohmayer, used Suzaku's superb spectral capabilities to survey three neutron-star binaries: Serpens X-1, GX 349+2, and 4U 1820-30. This team observed a nearly identical iron line in Serpens X-1, confirming the XMM-Newton result. It detected similarly skewed iron lines in the other two systems as well.
"We're seeing the gas whipping around just outside the neutron star's surface," says Cackett. "And since the inner part of the disc obviously cannot orbit any closer than the neutron star's surface, these measurements give us a maximum size of the neutron star's diameter. The neutron stars can be no larger than 29 to 33 km across, results that agree with other types of measurements."
"Now that we have seen this relativistic iron line around three neutron stars, we have established a new technique," adds Miller. "It's very difficult to measure the mass and diameter of a neutron star, so we need several techniques to work together to achieve that goal."
Knowing a neutron star's size and mass allows physicists to describe the 'stiffness' (or equation of state) of matter packed inside these incredibly dense objects. Besides using these iron lines to test Einstein's general theory of relativity, astronomers can use them to probe conditions in the inner part of a neutron star's accretion disc.
European Space Agency
To address this mystery, scientists must accurately and precisely measure the diameters and masses of neutron stars. In two concurrent studies, one with XMM-Newton and the other with Suzaku, astronomers have taken a big step forward.
Using XMM-Newton, Bhattacharyya and his colleague Tod Strohmayer observed a binary system known as Serpens X-1, which contains a neutron star and a stellar companion. They studied a spectral line from hot iron atoms that are whirling around in a disc, just beyond the neutron star's surface, at 40% the speed of light.
Previous X-ray observatories detected iron lines around neutron stars, but they lacked the sensitivity to measure the shapes of the lines in detail.
Thanks to XMM-Newton's large mirrors, Bhattacharyya and Strohmayer found that the iron line is broadened asymmetrically by the gas's extreme velocity, which smears and distorts the line because of the Doppler effect and beaming effects predicted by Einstein's special theory of relativity. The warping of space-time by the neutron star's powerful gravity, an effect of Einstein's general theory of relativity, shifts the neutron star's iron line to longer wavelengths.
"We have seen these asymmetric lines from many black holes, but this is the first confirmation that neutron stars can produce them as well. It shows that the way neutron stars accrete matter is not very different from that of black holes, and gives us a new tool to probe Einstein's theory," says Strohmayer.
A group led by Edward Cackett and Jon Miller of the University of Michigan, which includes Bhattacharyya and Strohmayer, used Suzaku's superb spectral capabilities to survey three neutron-star binaries: Serpens X-1, GX 349+2, and 4U 1820-30. This team observed a nearly identical iron line in Serpens X-1, confirming the XMM-Newton result. It detected similarly skewed iron lines in the other two systems as well.
"We're seeing the gas whipping around just outside the neutron star's surface," says Cackett. "And since the inner part of the disc obviously cannot orbit any closer than the neutron star's surface, these measurements give us a maximum size of the neutron star's diameter. The neutron stars can be no larger than 29 to 33 km across, results that agree with other types of measurements."
"Now that we have seen this relativistic iron line around three neutron stars, we have established a new technique," adds Miller. "It's very difficult to measure the mass and diameter of a neutron star, so we need several techniques to work together to achieve that goal."
Knowing a neutron star's size and mass allows physicists to describe the 'stiffness' (or equation of state) of matter packed inside these incredibly dense objects. Besides using these iron lines to test Einstein's general theory of relativity, astronomers can use them to probe conditions in the inner part of a neutron star's accretion disc.
European Space Agency
Neutron Star News and Current Neutron Star Events RSSDiscovery of most recent supernova in our galaxy
The most recent supernova in our Galaxy has been discovered by tracking the rapid expansion of its remains. This result, using NASA's Chandra X-ray Observatory and NRAO's Very Large Array (VLA), has implications for understanding how often supernovas explode in the Milky Way galaxy.
NASA scientists identify smallest known black hole
Using a new technique, two NASA scientists have identified the lightest known black hole. With a mass only about 3.8 times greater than our Sun and a diameter of only 15 miles, the black hole lies very close to the minimum size predicted for black holes that originate from dying stars.
Powerful explosions suggest neutron star missing link
Observations from NASA's Rossi X-ray Timing Explorer (RXTE) have revealed that the youngest known pulsing neutron star has thrown a temper tantrum.
Jekyll-Hyde neutron star discovered by researchers
Like something out of a Robert Louis Stevenson novel, researchers at NASA and McGill University discovered an otherwise normal pulsar which violently transformed itself temporarily into a magnetar, a stellar metamorphosis never observed before.
Neutron stars can be more massive, while black holes are more rare, Arecibo Observatory finds
Neutron stars and black holes aren't all they've been thought to be. In fact, neutron stars can be considerably more massive than previously believed, and it is more difficult to form black holes, according to new research developed by using the Arecibo Observatory in Arecibo, Puerto Rico.
Astronomers find record-old cosmic explosion
Using the powerful one-two combo of NASA's Swift satellite and the Gemini Observatory, astronomers from a number of institutions, including Johns Hopkins, have detected a mysterious type of cosmic explosion farther back in time than ever before.
White Dwarf Pulses Like a Pulsar
New observations from Suzaku, a joint Japanese Aerospace Exploration Agency (JAXA) and NASA X-ray observatory, have challenged scientists' conventional understanding of white dwarfs. Observers had believed white dwarfs were inert stellar corpses that slowly cool and fade away, but the new data tell a completely different story.
Chandra discovers cosmic cannonball
One of the fastest moving stars ever seen has been discovered with NASA's Chandra X-ray Observatory. This cosmic cannonball is challenging theories to explain its blistering speed.
Stellar forensics with striking new image from Chandra
A spectacular new image shows how complex a star's afterlife can be. By studying the details of this image made from a long observation by NASA's Chandra X-ray Observatory, astronomers can better understand how some stars die and disperse elements like oxygen into the next generation of stars and planets.
Neutron stars warp space-time, U-M astronomers observe
Einstein's predicted distortion of space-time occurs around neutron stars, University of Michigan astronomers and others have observed.
More Neutron Star News Articles
 | An Introduction to Thermal Physics by Daniel V. Schroeder |
 | Neutron Star by Larry Niven |
 | Black Holes, White Dwarfs and Neutron Stars: The Physics of Compact Objects by Stuart L. Shapiro, Saul A. Teukolsky |
 | Gravity, Black Holes, and the Very Early Universe: An Introduction to General Relativity and Cosmology by Tai L. Chow |
 | Death of a Neutron Star (Star Trek Voyager, No 17) by Eric Kotani |
 | Schaum's Outline of Astronomy by Stacey Palen |
| Astrophysis of Compact Objects: International Conference on Astrophysics of Compact Objects (AIP Conference Proceedings) | |
| Neutron Star by Larry Niven | |
| Neutron Stars by Gregory Fitzgerald | |
 | General Relativity: With Applications to Astrophysics (Theoretical and Mathematical Physics) by Norbert Straumann |
| © 2008 BrightSurf.com |