RICHLAND — The latest operating run of the LIGO Hanford observatory near Richland hit the jackpot.
The network of its twin gravitational wave observatory in Louisiana and a detector in Italy picked up ripples in space and time created by 35 violent events in space between November 2019 and March 2020.
The data is confirmed and studied by three international collaborations of scientists based in the United States, Europe and Japan.
“Using these observations, we are closer to unlocking the mysteries of how stars, the building blocks of our Universe, evolve,” said Christopher Berry, a lecturer at the University of Glasgow.
The announcement of the discoveries come just six years after the Advanced Laser Interferometer Gravitational-wave Observatory, with detectors in Eastern Washington state and Louisiana, made its first discovery.
Gravitational waves passing through Earth from the collision of two black holes were detected in September 2015, some 40 years after the National Science Foundation started a project to detect them.
Their detection confirmed Albert Einstein’s 1916 prediction of gravitational waves in his theory of general relativity.
With the continued improvement of detectors, gravitational wave scientists have gone from the first detection of the ripples through space and time to observing many events each month and sometimes more than once on a single day.
“The third observing run saw gravitational wave detection becoming an everyday thing,” said Hannah Middleton, postdoctoral researcher at OzGrav, University of Melborne.
But each detection remains exciting, with the possibility that each observing run will bring surprises, she said.
Black hole mergers
The 35 detections in the latest observing run of the collaboration that includes LIGO Hanford was the most in the three runs since instrumentation was upgraded to what’s called Advanced LIGO.
They bring to 90 the total number of events observed, according to data published Sunday on ArXiv.
The latest run detected ripples from 32 events that were most likely black hole mergers.
In each, black holes spiraled around each other until finally joining together and emitting a burst of gravitational waves.
Two of the most recent detections were of much rarer events, the merger of what appeared to be neutron stars and black holes.
Only dual black hole mergers been observed until the most recent run of LIGO and Virgo.
Neutron stars are the dense remnants of dying stars that undergo catastrophic explosions as they collapse at the end of their lives.
Black holes are also the corpses of massive stars — ones that have collapsed under their own gravity. Black holes are more massive than neutron stars.
“Only now are we starting to appreciate the wonderful diversity of black holes and neutron stars,” Berry said. “Our latest results prove that they come in many sizes and combinations.”
The black holes had a range of sizes, with the most massive about 90 times the mass of our Sun.
Several of the black holes that resulted from mergers were more than 100 times the mass of our sun and are classified as intermediate black holes.
They had been theorized by astrophysicists, with the latest observations confirming that this new class of black holes is more common in the universe than previously thought, according to the collaboration of observatories.
Rare neutron star events
One of the two rare neutron star and black hole mergers also included unusual data.
The gravitational waves appeared to be from the merger of a black hole about 33 times the mass of our Sun and a neutron star with a very low mass, just slightly more than the mass of Our Sun.
It was one of the lowest-mass neutron stars ever detected, either using gravitational waves or more conventional electromagnetic observations.
The masses of black holes and neutron stars are key clues to how massive stars live their lives and die in supernova explosions, according to the LIGO and Virgo collaboration.
Scientists are not sure of the origin of the gravitational waves in the detection not characterized as one of the 32 black hole mergers or the two black hole and neutron star mergers.
It likely was the merger of a black hole with a very light black hole.
Previously no black holes have been discovered that are that light, which could indicate scientists may need to revise their theories about the size of stars that can collapse to make black holes.
But scientists have not ruled out that the gravitational waves detected were created by the merger of a black hole with a very heavy neutron star.
How LIGO detects waves
LIGO is a new type of observatory with no telescope required.
Two vacuum tubes extend for 2.5 miles at right angles across previously unused Hanford site shrub steppe land near the Tri-Cities. At the end of each tube, a mirror is suspended on fine wires.
A high power laser beam is split to go down each tube, bouncing off the mirrors at each end. If the beam is undisturbed, it will bounce back and recombine perfectly.
But if a gravity wave is pulsing through the Earth, making one of the tubes slightly longer and the other slightly shorter, the beam will not recombine as expected.
Scientists watching for a gravitational wave at LIGO Hanford also detect movement caused by many other things. They have to sort through vibrations caused by ocean waves on the Pacific Coast or water coming over McNary Dam in the spring.
That’s why there’s a twin facility. Findings at LIGO at Hanford can be compared with an identical LIGO 1,900 miles away in Louisiana. If a gravity wave passes through Earth, both LIGOs should detect it.
“The LIGO and Virgo detectors continue to improve with, for example, increased laser power and the installation of squeezed light,” said Madeline Wade, assistant professor of physics at Kenyon College in Ohio.
Squeezed light is a special quantum mechanical state of light that minimizes the uncertainty in the properties needed for gravitational wave measurements.
After the Advanced Virgo observatory came on line in spring 2017, additional data is available to confirm detections and help locate them in the night sky.
That can allow observatories that observe forms of light, including X-ray, ultraviolet, infrared and radiowaves, to also search for evidence of the events.
The LIGO and Virgo observatories are offline now for further improvements.
They are expected to begin a fourth run with advanced capabilities in the second half of 2022.
They will be joined by the KAGRA observatory in Japan.
