Get ready for gravitational waves all day, every day



In the sprawling As a concert venue that is our universe, black holes often collide to produce falls of cosmic cymbals called gravitational waves. These collisions, as well as other astronomical activities that generate these space-time disturbances, occur often enough that a wave ripples at any time in a part of the universe. But as the waves barely died when they reached the Earth, astrophysicists only managed to hear their first in 2015.

Once the researchers understood how to listen, they quickly progressed. By the end of last year, their L-shaped detectors, located in Washington, Louisiana and Italy, had captured 11 gravitational waves in total. In about ten years, they hope to detect about a gravitational wave a day. "We are reaching the goal we originally had 30 years ago," says physicist Fred Raab of Caltech, member of the gravitational wave laser interferometer observatory. (LIGO), which detected the first gravitational wave in 2015. just want to discover one. We wanted to measure these things as a routine tool. "

Their projects began to take shape: last Thursday, researchers affiliated with LIGO announced that they had obtained essential funding for the upgrade of their instruments. The National Science Foundation and its UK counterpart, UK Research and Innovation, promised them $ 35 million. These new funds, as well as several international efforts to build more detectors, mean that scientists should be about to drown in the data over the next decade.

The researchers hope that these data on gravitational waves will help them map the universe with richer details than ever before. This is because the signals provide information about the universe inaccessible via telescopes. In fact, physicists often compare gravitational waves to sounds: if telescopes are the eyes on the universe, gravitational wave detectors are the ears. With more sensory information about black holes, neutron stars and supernovae, researchers have a new data stream to study the expansion of the universe and the nature of dark matter, for example.

LIGO plans to use this money to upgrade its detectors in Washington and Louisiana into a new iteration called Advanced LIGO Plus. LIGO detects gravitational waves by combining several infrared laser beams along the L-arms of their detectors. The patterns of the laser beam change if a gravitational wave ripples through the arms to deform them. But to make them even more precise, the LIGO team plans to control the quantum properties of laser light waves in a process called "light compression". These new detectors should be able to listen to rumblings in a volume five times larger than normal. before.

Another strategy to collect more signals is to build more observatories. Detectors located at different locations and recording the same signal help researchers confirm that it is a gravitational wave. Plus, more detectors provide greater coverage of the universe. Depending on how its builders orient its L-shaped arms, a detector becomes sensitive to gravitational waves coming from a particular direction. Multiple detectors also allow researchers to extract more information from the data. For example, multiple signals from the same gravitational wave let you locate its origin more precisely, just as GPS uses multiple satellites to locate your location, says Jo van den Brand of VU Amsterdam, who runs an observatory based on gravitational waves based in Italy. like Virgo.

There are currently three detectors in the world: the two detectors of LIGO and Virgo. But another is soon online: astrophysicists are about to test a new gravitational wave observatory, called KAGRA, located in a cave about 200 km west of Tokyo. They unveil a new technology – mirrors cooled to about 20 degrees above absolute zero – that gravitational researchers believe can be crucial for all future detectors. They plan to start observing in the fall of 2019, says physicist Takaaki Kajita of the University of Tokyo, who leads the collaboration.

LIGO has also begun construction of another gravitational wave observatory about 300 miles east of Mumbai, India, which is expected to be operational by 2025. The team began planning this site in 2010, says Raab. , and built most of India's detector at the same time as those in Louisiana and Washington in anticipation of a third future installation abroad. The time of this detector seems to have arrived: Raab is currently seeking to ship "hundreds of thousands of lasers, photodiodes, mirrors and non-fixed components" from Washington to India. Once built, it should be almost identical to the LIGO observatories in the United States.

These international teams will collaborate to make the most of the science of their signals. The members of LIGO and Virgo already meet regularly and have even merged their data analysis teams. Once the Japanese detector has shown sufficient sensitivity, they plan to join him.

Together, they are working on a quick protocol to alert the community of interesting signals, says Raab. They hope to reach a point where a gravitational wave crossing the Earth will be picked up by one detector, then the next, then a third, every millisecond. They would transmit these signals to an automated system for reporting false positives. Once the signal passed the test, the automated system warned observatories around the world to look for the visual origin of the gravitational wave in one minute. They would rotate their telescopes to watch and try to capture the universe in action.


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