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E. Washington astronomers chalk up new black hole discovery that sent ripples through time

By Annette Cary, Tri-City Herald
Published: May 26, 2023, 6:00am

KENNEWICK — The LIGO Hanford observatory was set to officially start another operating run Wednesday but it may have already made another significant detection of a violent event long ago in outer space.

With upgrades to the Laser Interferometer Gravitational-wave Observatory in Eastern Washington near Richland, several hundred more detections are expected in its planned 20-month operating run, said Michael Landry, head of LIGO Hanford Observatory.

That would more than double the detections made to date, helping to further unlock the mysteries of the universe.

The observatory on unused land at the Hanford nuclear reservation site detects gravitational waves from the collisions of black holes and neutron stars that send ripples through space and time.

The increased sensitivity also will help scientists to extract more physical information from the data the observatory collects, which will allow them to better test Albert Einstein’s general theory of relativity and infer the nature of the true population of dead stars in the local universe.

The LIGO Hanford Observatory in Eastern Washington’s first detection of gravitational waves, made in conjunction with a twin LIGO observatory in Louisiana, in 2015 provided physical confirmation of Einstein’s theory of relativity a century earlier.

That history-making detection of two black holes colliding was made during an engineering run to prepare for the first operating run of Advanced LIGO, a major upgrade to increase the sensitivity of detectors after the first generation LIGO detectors that operated for nine years without identifying any gravitational waves.

The latest possible important discovery was also during an engineering run that began several weeks ago as LIGO Hanford was preparing for the official start of its fourth Advanced LIGO operating run.

Several observations have been made during the engineering run that will be studied further, but the most interesting was on the morning of Thursday, May 18, and warranted notice to astronomers.

LIGO may have detected a neutron star being consumed by a black hole.

Light and gravitational waves

In the first three operating runs of Advanced LIGO, 90 detections of gravitational waves was made. All but 11 of them were in the third operating run as improvements increased the observatory’s sensitivity.

But just one detection of those 90 was also observed not only through its gravitational waves, but also light, giving scientists a new way to learn about the universe.

The fiery merger of two neutron stars was detected in 2017.

As they crashed together at the end of the Jurassic period on Earth, they flung debris outward. LIGO data was quickly analyzed to determine what area of the sky to search for light, and astronomers all over Earth were able to spot glowing gold, platinum and uranium created from radioactive decay in the blast.

The LIGO observatories also have made a second detection of a neutron star merger, a couple of detections of neutron star and black holes merging and a few events that scientists are not sure whether they were a black hole merger with a very heavy neutron start or a very light black hole.

Most of the detections have been two black holes merging. Those events, while important, do not give off light and cannot be observed by telescopes.

Scientists are hoping that with the increased sensitivity produced by the upgrades at LIGO over the past three years of down time, that there could be more gravitational waves detected from events that also can be seen with conventional astronomy.

Hanford LIGO improved

The goal of upgrades over the last three years was to improve the sensitivity to pick out a gravitational wave generated by merging neutron stars in the universe up to a range of about 520 to 620 million light years away.

However, as the fourth operating run is set to begin, that level of sensitivity has not been achieved. LIGO Hanford has the ability to detect events at 475 to 490 million light years. That’s up from 400 million light years away of 2019.

However, Landry believes that the observatory will be able to reach the target range as changes and improvements are made as it operates.

The major upgrade over the last three years was improving the process called “squeezing” that helps scientists gather better data.

At LIGO Hanford 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 glass fibers.

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 gravitational wave is pulsing through the Earth, making one of the tubes repeatedly infinitesimally longer and the other infinitesimally shorter, the beam will not recombine as expected.

But other things than gravitational waves can influence the laser beam.

LIGO’s laser is made of photons, each under the influence of vacuum fluctuations that can produce a crackle in the interferometer, limiting the range of detections.

That interference can be reduced by “squeezing” out quantum noise by creating a quantum state of light and injecting it into the vacuum tubes.

The quantum squeezing device was used in the previous operating run. But now it has been improved with the addition of a 984-foot tunnel along one of the LIGO arms that allows the further reduction of quantum noise at more frequencies.

Other work to improve detection sensitivity has included increasing the input laser power, changing out mirrors that had tiny imperfections in their coating and adding baffles to reduce excess light in the interferometer.

The twin LIGOs in the United States are expected to be joined in the start of the latest operating run by the KAGRA observatory in Japan and eventually by the Virgo observatory in Italy.

Visit LIGO Hanford

The new LIGO Exploration Center, or LExC, at the observatory is open Tuesdays through Fridays from 9:30 a.m. to 4 p.m.

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Interactive exhibits help children and adults learn about basic science research, gravitational waves, black holes and neutron stars, plus some of the principles of physics that are being used to detect infinitesimal gravitational waves that pass through Earth.

A giant Slinky stretches across the room for a hands-on demonstration of what happens to waves of traveling energy.

Rubber balls can be dropped to roll and spin around each other in a gravitational field.

A wave machine can be manipulated to show who the amplitude of gravitational waves are affected by the energy from the event that caused them and by the distance the wave has traveled.

The center, which debuted a year ago, should only get better.

A recently approved Washington state budget includes $2 million for exhibits at the center.

The public also can tour the observatory on the second Saturday of each month. A walking tour of about an hour and a staff talk is included, plus a chance to visit the LIGO Exploration Center.

The next tour is June 10 with multiple start times from 9:30 a.m. to 1:15 p.m. It is free, but registration is required at ligo.caltech.edu/WA/page/lho-public-tours.

LIGO is at 127124 N. Route 10, Richland. Take Highway 240 northwest from Richland and turn north on Route 10 just north of the Wanawish/Horn Rapids Dam.