Observations
Based on current models of astronomical events, and the predictions of the general theory of relativity, gravitational waves that originate tens of millions of light years from Earth are expected to distort the 4 kilometer mirror spacing by about 10−18 m, less than one-thousandth the charge diameter of a proton. Equivalently, this is a relative change in distance of approximately one part in 1021. A typical event which might cause a detection event would be the late stage inspiral and merger of two 10 solar mass black holes, not necessarily located in the Milky Way galaxy, which is expected to result in a very specific sequence of signals often summarized by the slogan chirp, burst, quasi-normal mode ringing, exponential decay.
In their fourth Science Run at the end of 2004, the LIGO detectors demonstrated sensitivities in measuring these displacements to within a factor of 2 of their design.
During LIGO's fifth Science Run in November 2005, sensitivity reached the primary design specification of a detectable strain of one part in 1021 over a 100 Hz bandwidth. The baseline inspiral of two roughly solar-mass neutron stars is typically expected to be observable if it occurs within about 8,000,000 parsecs (26,000,000 ly), or the vicinity of our Local Group of galaxies, averaged over all directions and polarizations. Also at this time, LIGO and GEO 600 (the German-UK interferometric detector) began a joint science run, during which they collected data for several months. Virgo (the French-Italian interferometric detector) joined in May 2007. The fifth science run ended in 2007. It is hoped that after extensive analysis, data from this run may uncover two unambiguous detection events. This would be a milestone in the history of physics. In 2004, it was reported that theorists estimated the chances of an unambiguous direct detection by 2010 at one in six.
In February 2007, GRB 070201, a short gamma-ray burst, arrived at Earth from the direction of the Andromeda Galaxy, a nearby galaxy. The prevailing explanation of most short gamma-ray bursts is the merger of a neutron star with either a neutron star or black hole. LIGO reported a non-detection for GRB 070201, ruling out a merger at the distance of Andromeda with high confidence. Such a constraint is predicated on LIGO eventually demonstrating a direct detection of gravitational waves.
In August 2010 a radio pulsar was discovered through analysis of data from radio telescopes by the LIGO collaboration. The detection was made using the "Einstein@home" personal computer collaboration through LIGO and BOINC. Although significant, discovery of this radio pulsar was not a detection of gravitational waves nor did it involve the LIGO interferometers.
Read more about this topic: LIGO
Famous quotes containing the word observations:
“The natural historian is not a fisherman who prays for cloudy days and good luck merely; but as fishing has been styled “a contemplative man’s recreation,” introducing him profitably to woods and water, so the fruit of the naturalist’s observations is not in new genera or species, but in new contemplations still, and science is only a more contemplative man’s recreation.”
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