LIGO Hanford has a new partner in its search for gravitational waves created by violent events in space.
Scientists are expecting the expanded network to lead to more detections of ripples through space and time and an improved ability to search for evidence of events with light-based telescopes in addition to evidence found by gravitational wave observatories.
On Friday, the National Science Foundation and Europe’s Virgo signed an agreement to collaborate with Japan’s new Kamioka Gravitational-Wave Detector, called KAGRA.
That brings the cooperating observatories searching for gravitational waves to four, including the National Science Foundation’s laser-interferometer gravitational wave observatories on Hanford nuclear reservation land just north of Richland and its twin observatory in Louisiana.
“The more detectors we have in the global gravitational-wave network, the more accurately we can localize the gravitational-wave signals on the sky, and the better we can determine the underlying nature of cataclysmic events that produced the signals,” said David Reitze, of the California Institute of Technology, the executive director of the U.S. LIGO Laboratory.
In 2015 the Hanford and Louisiana detectors made scientific history by detecting the gravitational waves predicted by Albert Einstein 100 years earlier. The waves were created as two black holes spiraled toward each other and collided in a distant galaxy more than 1 billion light-years from Earth.
Since then, the two LIGO observatories and their original partner Virgo in Italy have had about 30 additional likely detections of gravitational waves, mostly from colliding black holes.
LIGO Hanford detects movement
LIGO Hanford and the other gravitational wave observatories watch for tiny movements of the Earth that appear to be caused by gravitational waves. The waves minutely stretch the Earth in one direction and contract it in another, in effect turning a circle into an ellipse.
The gravitational wave observatories, including the one built on unused land on the Hanford Site, look for that distortion.
At LIGO Hanford, two vacuum tubes, each 2.5 mils long, extend across the shrub steppe landscape northwest of Richland at right angles. At the end of each, a mirror is suspended on fine glass fibers.
A high-powered 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 detector arm and compress the other. The movement can be so small that it would take 10 trillion such movements to equal the width of a human hair.
Comparing data with other gravitational-waves helps confirm that such movements that are detected were from gravitational waves, rather than other movements, such as vibrations detected at Hanford caused by ocean waves across Washington state on the Pacific Coast.
New approach by Japan’s KAGRA
The gravitational-wave observatory in Japan is pioneering new approaches to the search for gravitational waves.
It will be the first kilometer-scale gravitational-wave observatory to operate underground, which will dampen unwanted noise from winds and seismic activity. It also will be the first to use cryogenically chilled mirrors, a technique that cuts down on thermal noise.
“These features could supply a very important direction for the future of gravitational-wave detectors with much higher sensitivities,” said Takaaki Kajita, principal investigator of the KAGRA project.
The fourth observatory also will allow detections to be narrowed down to patches of sky that are only about 10 square degrees, greatly enhancing the ability of light-based telescopes to search for light.
Although black hole collisions do not emit light, in 2017 the two U.S. LIGO observatories and Virgo were able to localize the source of the gravitational waves created by the fiery crash of two neutron starts to a patch of sky about 30 square degrees in size, or less than 0.1 percent of the sky.
Ground-based and space telescopes searching for different forms of light, or electromagnetic radiation — including X-ray, ultraviolet, infrared and radio waves — were able to pinpoint the galaxy where the collision occurred and observe the light from its aftermath.
It was the first time a cosmic event had been observed in both gravitational waves and light, creating the new field of “multi-messenger” astronomy.
KAGRA is currently in the commissioning phase after construction was completed in the spring. It is expected to come online for the first time in December, joining the current observing run of the U.S. LIGO and the Virgo observatories that began on April 1.
Initially, KAGRA is not expected to have the sensitivity to detect gravitational waves, but its performance will improve with time.
LIGO Hanford open for tours
The three operating gravitational-wave observatories, including the one at Hanford, have halted observations through the month of October to allow instrument upgrades and fixes. All three should be operational by Nov. 1.
At LIGO Hanford, 20-year-old vacuum pumps will be replaced, along with a fiber-optic cable that carries laser light, along with other fixes.
The work is intended to improve its ability to detect gravitational waves, which has been lagging behind the Louisiana detector in the current observing run.
The Livingston observatory is sensitive enough to potentially detect the merger of two neutron stars as far as 440 million light-years away, while the Hanford sensitivity is limited to a similar observance at about 380 million light-years.
The Hanford upgrades and fixes should close the gap considerably, according to officials.
The Hanford observatory is open once a month for public tours.
The next free monthly tour of LIGO Hanford will be Oct. 12. Walking tours that last about an hour start at 1:30 and 3:30 p.m. A LIGO staff member will give a talk at about 3 p.m.
To reach LIGO, search for “LIGO Hanford Observatory” on Google Maps. Or drive northwest from Richland on Highway 240 and turn right on Hanford Route 10 and drive about five miles.