Massive American machines, looking for ripples in space-time, have just been upgraded: NPR

Scientists are about to restart the two giant installations in the United States that record gravitational waves, the ripples of the very fabric of the universe predicted by Albert Einstein more than a century ago.

Einstein realized that when large objects such as black holes collide, the impact sends shockwaves in space – time that resemble ripples in the air. water created by throwing a pebble into a pond.

In 2015, researchers made history by detecting for the first time gravitational waves from colliding black holes. It was such an important event that three American physicists almost immediately won the Nobel Prize for their work.

Since then, physicists have detected gravitational waves from other exotic smells. The grand total is 10 pairs of black holes colliding, and a pair of neutron stars breaking together.

Now, they are preparing to discover more of these cosmic events. On April 1, the twin facilities of the state of Washington and Louisiana that make up the laser interferometer gravitational wave observatory will begin doing scientific research after being shut down for more than one year. so that workers can install hardware upgrades.

The improvements should dramatically increase the detector's ability to detect some of the most mysterious and powerful events in the universe.

"Until now, we've seen eleven things, maybe we'll see double this year," said Joseph Giaime, director of the LIGO Observatory in Livingston, La.

The researchers will also be helped by the fact that a third detector in Italy, called Virgo, will be operational. It was only online for the very end of LIGO's last observation period. The presence of more detectors allows researchers to more easily locate the source of gravitational waves in the sky. In addition, a new detector in Japan, called KAGRA, should be used at some point.

Being able to detect gravitational waves is a novelty for astronomy, which has been studying light for centuries. But black holes do not emit light and these detectors offer a new way to probe their secrets.

"Galileo invented the telescope or used the telescope for the first time in astronomy 400 years ago, and today we are building better telescopes," says Gabriela González, professor of physics and astronomy at Louisiana State University. "I think this decade was the beginning of gravitational wave astronomy, so it will continue to progress, with better detectors, different detectors, more detectors."

She worked on gravitational waves for years before they were actually detected, and says friends now confess to worrying about her career because the task was so difficult that it seemed like the waves could never be detected. Now, she says, they are jealous that she is working in such a sharp area.

Each LIGO detector in the United States is made up of two long concrete pipes that form a huge letter "L." Each arm extends for more than two miles. "I've talked to booster pilots who are wondering why a pipeline does not start anywhere, travels a few miles, turns right and does not get anywhere either," said Giaime.

Inside the pipeline is a powerful laser beam that goes back and forth between the mirrors. Scientists use this laser to accurately measure the length of each arm of the L. When a gravitational wave passes through and distorts the gap, the lengths change from a tiny bit – a fraction of the width of a subatomic particle.

According to Giaime, some of the recent detectors upgrades include hardware types that increase the power of the laser and reduce certain types of "noise" in their measurements. "We replaced some optics, which is a lot of work," he says.

This time, if LIGO detects gravitational waves, the team will send public alerts so that everyone can point their telescope to the right place in the sky just in case, as in the case of the collision between a neutron star , an observable fireworks.

"We have only seen this handful of black holes among all those possible.There are many questions we still do not know how to answer," says Nergis Mavalvala, a gravitational wave researcher at MIT.

In addition, she says, there is always the possibility that something completely unexpected happens and leaves researchers perplexed scratching their heads.

"That's how discovery happens," she says. "You turn on a new instrument, you point it to the sky and you see something you have no idea."