Far out cosmology: LIGO detector explained (Introduction)

by David Turell , Wednesday, January 13, 2016, 22:28 (3235 days ago) @ David Turell

It appears there are several new detectors around the world:-http://blogs.scientificamerican.com/guest-blog/the-waves-no-one-can-find/?WT.mc_id=SA_WR_20160113-"One of the best hopes for achieving the necessary sensitivity is light. In a technique known as interferometry, a laser beam is split to send two light waves down perpendicular tunnels several kilometers in length. The waves reflect off mirrors to return to the same position and recombine. The intensity of the newly recombined beam depends on the alignment (or phase) of the peaks and troughs in the two waves. This makes it incredibly sensitive to how far each wave has traveled before it recombines.-"For gravitational wave detection, the tunnel lengths ensure that the peaks from one wave meet the troughs from the second wave. This is known as destructive interference and it cancels the light of the recombined wave entirely. But when a gravitational wave passes, it distorts the lengths of the tunnels, changing how far each wave travels. The peaks and troughs of the two light waves then no longer perfectly align; the beams no longer cancel each other, and a signal is produced.-***-"Buried 200 m below the Ikenoyama mountain in the Gifu prefecture of Japan, the Kamioka Gravitational Wave Detector (KAGRA) is about to turn on its lasers for the first time. Led by the 2015 Physics Nobel Laurette, Takaaki Kajita, KAGRA's sensitivity should allow it to detect gravitational waves up to 700 million light years away, ten times further than the previous generation of detectors. Its main target will be binary neutron stars; incredibly dense stellar corpses that emit energy in the form of gravitational waves as their orbits around each other decay. Its enormous range means it's not restricted to events only in our own galaxy, so KAGRA should detect multiple gravitational wave events per year.-"KAGRA's underground location minimizes seismic noise from the ever-rumbling Japan. The surrounding gneiss rock is famous for its hardness, causing the mountain to act as a single entity that is resistant to shakes. KAGRA's second new feature is cryogenic cooling, bringing the system down to an frosty -253° Celsius (20 K), to stifle any thermal vibrations."