Gravity wave detectors detect more black hole mergers

Since the many improvements to improve sensitivity, gravitational wave detectors in the United States and Europe have detected slight undulations in the structure of space, which seem to indicate the fusion of three black holes, a collision between two Ultra-compact neutron stars and the possible fusion of a black hole and a neutron star, scientists said Thursday.

"This series opens a new era in gravitational wave astronomy, in which detection candidates are made public as quickly as possible after data collection," said Patrick Brady, professor of physics at the University of Toronto. University of Wisconsin-Milwaukee and spokesperson for the LIGO Scientific Collaboration.

"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," he said. Brady. "So far, three of the detection candidates are compatible with similar binary black hole mergers at 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 fifth candidate, detected a day later, is less certain, but could represent the fusion of a neutron star and a black hole, a phenomenon never observed before. At an estimated distance of more than one billion light-years from Earth, the signal is weak, even by gravitational wave standards.

Artist's view of two neutron stars colliding.

NSF / LIGO / Sonoma State University / A. Simonnet

"The fifth candidate (…) allows the intriguing possibility that it comes from the collision of a neutron star with a black hole," said Brady. "Unfortunately, this candidate is rather weak and it will take us some time to come to a solid conclusion."

Additional analyzes are planned and astronomers around the world are looking for traces of fusions in the electromagnetic spectrum, assuming that such traces are within reach of current instruments. The search is difficult because the gravity wave data indicate only a general area of ​​the sky and not a specific point of space.

In the meantime, including the first detection of gravitational waves from a black hole melting detected in 2015, the LIGO and Virgo detectors have now collected evidence of 13 black hole mergers, two neutron star collisions and a possible fusion of black holes and neutron stars.

"The highlight of our current situation is that we are just beginning to see the field of gravitational wave astronomy open," Brady told reporters at a teleconference. "As detectors experience a slew of enhancements over the next decade, we will have the ability to see things in the entire universe, perhaps the ability to measure the gravitational waves of the world. rotating neutron stars and even things we did not think of serious sources.

"And it's a great thing for us." Opening a new window to the universe like this will bring us, hopefully, a whole new perspective on what's out there … As and When As we see more of these events, we will be able to essentially understand how stars die and how neutron stars and black holes form as end products of stellar evolution. new and exciting things we hope to master using gravitational waves. "

The Laser Interferometer Gravitational Wave Observatory, or LIGO, operated by Caltech and MIT with funding from the National Science Foundation, includes two observation stations, one in Washington and the other in Louisiana. Each LIGO station consists of a pair of L-shaped, 2.5-km-long vacuum tubes in which precisely tuned laser beams come and go between several mirrors, effectively increasing the distance traveled by each beam up to the point where it is possible. at almost 1,000 km. The laser beams are then recombined and directed into a sensor.

The LIGO gravity detector near Hanford, Washington State. A second identical observatory is located near Livingston, Louisiana, with a third facility, called Virgo, at the European Gravitational Observatory, near Pisa, Italy.

Caltech Laboratory / MIT / LIGO

The Virgo detector of the European Gravitational Observatory, near Pisa, Italy, works in the same way, with slightly shorter arms.

In the absence of detectable gravitational waves, the light in each vacuum tube travels exactly the same distance before being recombined and the detectors do not "see" anything – the system is configured in such a way that the crests of the light beams of a vacuum tube match. with the hollows of the other, creating a destructive interference.

But according to Einstein, a gravitational wave will extend space in one direction and compress it in a perpendicular direction. The effect on LIGO and Virgo is to stretch the space between the mirrors in one vacuum tube and shrink 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 allows scientists to determine the distance and direction of the event that generated the waves and the masses involved. The first black hole melting detected by LIGO in 2015 directly converted the solar mass directly into energy in a burst of 20 milliseconds.

The alleged fusion of neutron stars detected during the last observational campaign would have occurred about 500 million light years from Earth. The possible fusion between the neutron and the black hole occurred about 1.2 billion light years away.