Richland observatory detection shows shape of black hole ripples

The Hanford LIGO observatory near Richland has done it again.

It has detected gravitational waves for the fourth time, starting with an initial discovery in September 2015, researchers announced Wednesday.

The latest gravitational waves observed came from the merger of two black holes, just as in the three previous detections.

During the final moments of the black hole collision, it created gravitational waves, or ripples in the fabric of time and space, that would travel through the Earth 1.8 billion light-years away.

But this time scientists were able to learn more about the gravitational waves and the event behind it because the detection was made for the first time by three observatories around the globe.

Collecting data at three sites “will allow us to understand many more things about the universe we live in,” said Giovanni Losurdo, Advanced Virgo project leader for the Virgo Collaboration, speaking through an interpreter.

The waves were observed in data collected both by the twin Laser Interferometer Gravitational-wave Observatories at Hanford and in Louisiana, and also by the Virgo detector near Pisa, Italy.

The Virgo detector came on line after extensive upgrades Aug. 1 to join the U.S. LIGOs, and the three-detector observation was made with data collected on Aug. 14. The gravitational waves passed through the observatory near Richland early in the morning.

By having observations at Virgo, in addition to the two LIGO observatories, scientists can better determine how the space-time continuum is distorted in three dimensions, said Frédérique Marion, senior scientist with the Virgo Collaboration.

Analysis of the signal shows it is consistent with the polarization allowed by Albert Einstein’s theory of relativity, with space stretching in one direction and contracting in another, she said. The waves would turn a circle into an ellipse.

Having three detectors available to collect data also helps scientists narrow the area of the sky where the gravitational waves originate and improves the accuracy of information about how far they have traveled.

The gravitational waves were detected on Aug. 14, first at the Livingston, La., observatory. A few thousandths of a second later, they were detected at the Hanford LIGO and shortly after that at the Virgo observatory.

The different times equate to different distances, said David Shoemaker, of the Massachusetts Institute of Technology, the spokesman for the LIGO scientific collaboration. He compared the three distances to the legs of a tripod that could be followed back to where the legs of the tripod meet to give an idea of where the black holes merged.

Having three detectors rather than two shrinks the volume of the universe where the black holes could have merged by a factor of 20, scientists said.

“A smaller search area enables follow-up observations with telescopes and satellites for cosmic events that produce gravitational waves and emissions of light, such as the collision of neutron stars,” said Laura Cadonati, of Georgia Tech, the deputy spokeswoman of the LIGO scientific collaboration.

Black holes produce gravitational waves, but not light.

The black holes that created the gravitational waves detected on Aug. 14 had masses about 31 and 25 times the mass of our sun. The newly produced spinning hole has about 53 times the mass of the sun, which means that about three solar masses converted into gravitational-wave energy.

Over the next year, the Hanford and Louisiana observatories will be fine tuned to increase their sensitivity as much as a factor of two, which would increase the volume of space that can be searched for events that create gravitational waves by eight times.

“This is just the beginning of observations with the network enabled by Virgo and LIGO working together,” Shoemaker said. “With the next observing run planned for fall 2018, we can expect such detections weekly or even more often.”

The LIGO near Richland has two vacuum tubes that extend for 2.5 miles across the Hanford shrub steppe landscape north of Richland at right angles. At the end of each, 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 powerful enough gravitational wave is pulsing through the Earth, the beam will be disturbed as the waves slightly stretch one vacuum tube and compress the other. The movement is so small that it would take 10 trillion such movements to equal the width of a human hair.

The U.S. LIGOs were paid for by the National Science Foundation, which has been pursuing the detection of gravitational waves for four decades. The Virgo collaboration has physicists and engineers from 20 different European research groups.

Additional gravitational-wave observatories are planned in Japan and India.

“It looks to me like the future is incredibly bright for Virgo, for LIGO, for the Virgo-LIGO network, for gravitational wave astronomy and then for the greater astronomical environment, which we can now do in common with gravitational waves and with electromagnetic radiation,” Shoemaker said.

This story was originally published September 27, 2017 at 9:30 AM with the headline "Richland observatory detection shows shape of black hole ripples."