LIGO didn't "see" anything. It monitors the relative lengths of the paths taken by two laser beams in vacuum pipes about 4km long (although the laser path consists of about 75 trips up and down the arms) and at right angles to each other.
A gravitational wave, travelling at the speed of light, changes the ratio of these lengths (one gets shorter, one gets larger, then they swap) by about plus or minus 1 part in $10^{21}$ (a billion trillion) about 30-200 times per second as it passes through the instrument.
The whole event lasted about 0.3 seconds and the trace (which has been all over the news) simply records the fraction by which the length of the arms changes as a function of time.
The event was (nearly) simultaneously recorded by two almost identical setups in different parts of the USA. The detection of the same signal in both detectors rules out a local cause of the disturbance, and the small time delay between the detections allows a rough location of the gravitational wave source on the sky.
No comments:
Post a Comment