Improved LIGO and Virgo stations observe several gravity waves – Astronomy Now

After major improvements, the LIGO and Virgo gravitational wave detectors offer five possible events in just one month of observation: three black hole fusions, a collision between two compact neutron stars and, on April 26th, a possible collision between a neutron star and a black. hole. If confirmed, the observation would mark another first in the emerging field of gravitational wave astronomy.

"The universe keeps us on our guard," said Patrick Brady, chief spokesman for the LIGO scientific collaboration, in a statement. "We are particularly curious about the April 26 candidate. Unfortunately, the signal is rather weak. It's like listening to someone whispering a word in an animated cafe, it can be difficult to distinguish the word or even to be sure the person is whispering. It will take some time to reach a conclusion about this candidate. "

The laser interferometer gravitational wave observatory, or LIGO, is operated by Caltech and MIT. It consists of two observation stations, one in Washington State and the other in Louisiana, both equipped with a pair of L-shaped 4 km long vacuum tubes. Virgo from the European Gravitational Observatory, near Pisa, Italy, has slightly shorter arms.

The laser beams emitted along each arm bounce between the mirrors, then are recombined and analyzed. The system is configured so that the peak of the light beams of one vacuum tube exactly matches the hollows of the other, thus creating destructive interference. In the absence of gravitational waves or any other external influence that can influence the distance traveled by the photons, the light in each vacuum tube covers exactly the same distance before being recombined. In this case, the detectors do not "see" anything.

But according to Einstein's theory of general relativity, a gravitational wave crossing the Earth would extend space in one direction and compress it in a perpendicular direction, stretching the gap between the mirrors of a vacuum tube and reducing it. slightly in the other.

Since laser beams travel slightly different distances when passing a wave, peaks and valleys no longer match when beams are recombined. The resulting interference pattern can be analyzed to determine exactly the extent and decrease of the contraction.

This, in turn, allows reverse engineering scientists the kind of event needed to generate such distortions and even to determine their general direction. Other observatories can then search for electromagnetic radiation from such events to obtain additional information and locate their locations.

The recent upgrades of LIGO and Virgo have improved their sensitivity, allowing astronomers to detect more gravity wave events and hopefully that much more mundane phenomena than black hole fusion will soon be at hand .

"This series opens a new era in gravitational wave astronomy, in which detection candidates are made public as quickly as possible after data collection," Brady told reporters at a teleconference. who announced the new results.

"In just one month of observation, we identified five candidates for gravitational wave detection … made possible by the substantial improvements made to the LIGO and Virgo detectors over the last 18 months. So far, three of the detection candidates are compatible with binary black hole mergers similar to the first event discovered in 2015. The fourth candidate, discovered on April 25, is expected to come from the fusion of two neutron stars. "

The LIGO and Virgo detectors have now collected evidence of 13 total black hole mergers, two neutron star collisions and a possible black hole and neutron star melting.

"The plus point about our current situation is that we are just beginning to see the field of gravitational wave astronomy open," Brady said. "As the detectors will experience a series of improvements over the next decade, we will have the opportunity to see everything happening in the universe, perhaps measuring the gravitational waves of the world. rotating neutron stars and even things we had not thought of from serious sources yet.

"And that's very important to us. Opening a new window on the universe like this one will hopefully give us a whole new perspective on what exists. … As we see more events, we can essentially understand how stars die and how neutron stars and black holes are formed as end products of stellar evolution. We hope to be able to master a lot of new and exciting things using gravitational waves. "