Gravitational Waves of Neutron Stars
Neutron stars are formed from the gravitational collapse of massive stars undergoing a supernova. Although somewhat rare, they are of great interest due to physics involved. Instead of being composed of normal matter, they are almost entirely neutrons. They are very dense, but do not collapse into a black hole due to the Pauli exclusion principle. It has been widely theorized that these objects could emit gravitational waves (GWs) due to their incredible density, but only if they are rotating quickly.
A direct consequency of the theory of general relativity, GWs are small perturbations in space-time. Because nothing travels faster than light, changes in a gravitational field must also propagate at or below this speed. These waves are analogous in many ways to electromagnetic waves, leading many to talk about them as the theory of gravitational radiation. GWs have not been directly observed to date, but are a subject of intense research and debate amongst the scientific community. Many are excited because they think we are close to detecting these GWs. Several experiments that are currently underway to accomplish this goal:
LIGO - Laser Interferometer Gravitational Wave Observatory
VIRGO - kilometer scale Michelson interferometer with Fabry-Perot arms in Italy
GEO - German/UK experiment
LISA - Laser Interferometer Space Antenna
While many sources of GWs are subject to investigation, those that are generated by rotating neutron stars are some of the most promising.
A paper by Worley, Krastev, and Li entitled Nuclear Constraints on gravitational waves from rapidly rotating neutron stars, recently submitted to Arxiv, explores what these GWs would be like. In particular, they determine a theoretical upper limit on the strain-amplitude of GWs emitted by rapidly rotating neutron stars. For a full explanation of strain-amplitude, see source number 2.
Their establishment of the upper limit of this property makes it easier to predict what GWs will look like in the vicinity of Earth for the fastest pulsars currently known of. They end their paper by saying, “These predictions serve as the first direct nuclear constraint on the gravitational waves from rapidly rotating neutron stars.” With a little luck and a lot more hard work, gravitational waves from all types of sources will soon be directly observed.
Sources:
1. Worley A., Krastev P.G., Li Bao-An. Nuclear Constraints on Gravitational waves from rapidly rotating neutron stars. Arxiv December 2, 2008
2. Plamen G. Krastev, Bao-An Li, and Aaron Worley, Phys. Lett. B 668, 1 (2008).
This entry was posted on Thursday, December 4th, 2008 at 8:28 pm and is filed under Astrophysics, Nuclear Physics. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
