Upgraded gravitational-wave detector begins operations

New Scientist : On Friday, the Advanced Laser Interferometer Gravitational-Wave Observatory (Advanced LIGO) began operations after five years of downtime during which upgrades were made to the original LIGO system. Advanced LIGO is looking for the ripples in spacetime predicted by general relativity to occur when massive objects move quickly. One such case, when two neutron stars spiral around each other, may occur only once every 30 000 years in a given galaxy. The detector operates by bouncing identical lasers between mirrors in two L-shaped tunnels separated by roughly 3700 km. As a gravitational wave passes through Earth, it will pass through the lasers at different times and alter the time the lasers take to bounce back and forth. The original LIGO run from 2002 to 2010 did not find any such signal, but it was looking at an area that included only 100 galaxies. The upgraded system, when it reaches its full capability, will be examining a volume that includes 300 000 galaxies, meaning it could see a signal as often as once per month.