Scientists are again searching for the ripples of space and time known as gravitational waves at the LIGO observatory near Richland, after making the first two direct observations of the waves in its previous operating run.
The Laser Interferometer Gravitational-wave Observatory, or LIGO, transitioned from engineering test runs to full science observations at 8 a.m. Wednesday at Hanford.
Its twin observatory in Livingston, La., began searching at the same time. When one of the LIGO observatories detects movement that could be caused by gravitational waves passing through Earth, a near identical detection at the other laboratory can confirm it.
Gravitational waves are caused by violent events in space, such as the mergers of pairs of neutron stars or black holes, or by supernovae.
Detecting the waves as they ripple through Earth holds promise to open up a new way for scientists to learn about the universe, much of which may be made up of matter unlike what we’re familiar with on Earth.
The previous LIGO search, conducted from September 2015 to January 2016, resulted in the first observation of gravitational waves 100 years after Albert Einstein predicted their existence.
On Sept. 14, 2015, the two LIGOs detected gravitational waves reaching the Earth from the collision of two black holes 1.3 billion light years away. Three months later, on Christmas Day, gravitational waves were detected for a second time.
We are only just now, thanks to LIGO, learning about how often events like these occur.
Dave Reitze, executive director at LIGO Laboratory
“With our improved sensitivity, and a longer observing period, we will likely observe even more black-hole mergers in the coming run and further enhance our knowledge of black-hole dynamics,” said Dave Reitze, executive director of the laboratory that operates the two observatories.
“We are only just now, thanks to LIGO, learning about how often events like these occur,” he said.
The detections of gravitational waves in 2015 followed major technical upgrades to make the observatories 10 times more sensitive in a project called Advanced LIGO. The two U.S. LIGOs had operated from 2002 to 2010 without detecting gravitational waves.
Since the end of the initial run under Advanced LIGO, the staff has been evaluating the observatories’ performance and making improvements to its lasers, electronics and optics.
“LIGO Hanford scientists and engineers have successfully increased the power into the interferometer and improved the stability of the detector,” said Mike Landry, the new head of LIGO at Hanford.
Progress has been made for using higher power in the future, which will improve sensitivity, or range, in runs that will follow the current one, he said. Improvements to the Livingston detector have provided 25 percent greater sensitivity than in previous runs.
Gravitational waves are powerful enough to compress objects as they pass through, turning a circle into an ellipse.
The LIGOs are designed to detect that tiny movement using high-powered laser beams bounced off mirrors suspended at the end of two 2.5-mile vacuum tubes stretching into the Hanford shrub steppe.
LIGO is designed to detect a change in distance between its mirrors 1/10,000th the width of a proton. This is equivalent to measuring the distance to the nearest star to an accuracy smaller than the width of a human hair.
The laser beam is split with half going down each of the tubes, which are arranged at right angles to catch any lengthening of one and shortening of the other by a gravitational wave. If the mirrors change distance, the beam will not perfectly combine as its two parts bounce off the mirrors and return.
Among improvements at the Hanford LIGO are specialized sensors in the corner and end stations of the tubes to make the detector more stable against wind and low-frequency seismic motion. The improvement will increase the amount of time the detector is in operating mode, Landry said.
As the observatories continue to improve and detect more black hole mergers, scientists will be able to learn more about pairs of black holes, including how many there are, their masses and spin rates. LIGO scientists also hope to detect the merger of neutron stars, which are the dense cores of exploded stars.
The engineering test runs of LIGO Hanford for the second observation period of Advanced LIGO started Nov. 14, and it is expected to run for about six months following the official start Wednesday.
Fred Raab, the former head of LIGO Hanford, has been promoted to associate director for operations for LIGO Laboratory, which operates the two observatories. Landry, the former lead detection scientist at LIGO Hanford, has Raab’s former position.
The National Sciences Foundation has been working on gravitational wave detection for more than 40 years, spending about $1 billion.