Jets and debris from a neutron star collision
The collision of four more sets of black holes have been detected via their gravitational waves at the LIGO observatory near Richland.
It brings the discoveries of the Laser Interferometer Gravitational-wave Observatory on the Hanford site to 10 black hole mergers and one merger of neutron stars.
“The rate of discovery suggests the most spectacular findings are yet to come,” said Denise Caldwell, director of the National Science Foundation.
The LIGO observatory at Hanford and its twin in Livingston, La., detect gravitational waves, or ripples through time and space, passing through Earth sometimes billions of years after cataclysmic events in outer space.
Rather than using telescopes to study space, the observatories rely on lasers to detect minute movements caused by gravitational waves to advance knowledge of astronomy and physics and learn more about the nature of time and space,
The observatories detected gravitational waves for the first time in September 2015 after four decades of development and then operation of the two LIGO observatories.
The detection confirmed Albert Einstein’s theory of relativity almost 100 years after he predicted the existence of gravitational waves.
The latest findings were discussed at a scientific conference on Saturday and then widely announced on Monday.
Ten of the series of rippling gravitational waves detected were created by black holes that spiraled toward each other until they collided.
The other was created by a different type of galactic collision, the fiery crash of two neutron stars. Neutron stars are the collapsed cores of large stars and are the smallest, densest stars known to exist.
“Getting to 10 events is a big milestone,” said Michael Landry, head of LIGO Hanford. “It allows us to apply statistics to observances and learn more about the objects.”
The four latest observances of black holes were made during an operating run of the National Science Foundation’s Hanford and Louisiana observatories while the European-based Virgo gravitational-wave observatory also was operating.
In the recent operating run, the LIGO observatories searched for gravitational waves from late November 2016 to late August 2017, detecting a total of seven black hole mergers and the observatories’ first merger of neutron stars.
Among the four black hole collisions announced Monday was the most massive and distant one yet detected.
On July 29, 2017, gravitational waves from a collision about 5 billion years ago was measured.
“The more massive they are, then the gravitational wave signal they produce is larger,” Landry said. It allows LIGO to detect waves that have traveled farther before they diminish to a power too faint to detect.
This one converted the equivalent energy of almost five solar masses into gravitational radiation.
Because there are now three gravitational observatories operating, the events can be more precisely located in the sky, Landry said.
During the first LIGO observatories’ operating run to detect gravitational waves, their location was narrowed down to about 1,000 square degrees in the sky. One of the most recent observances, of a black hole collision 2.5 billion light-years from Earth, was narrowed to 39 square degrees.
The smaller area makes traditional observatories, including those searching for light, more likely to be able to accurately spot the event.
When gravitational waves produced by a neutron star merger were detected on Aug. 17, 2017, other types of observatories were alerted.
About 11 hours later telescopes saw light and over the next two weeks other forms of light, or electromagnetic radiation , were observed, including X-ray, ultraviolet, infrared and radio waves.
It was the first time that a cosmic event had been viewed in both gravitational waves and light, giving scientists a new way of learning about the universe.
Telescopes that search for light in the night skies have not detected any of the LIGO-observed black hole collisions.
Black holes do not emit visible light when they merge.
However, some are surrounded with a disc of matter. If two black holes surrounded by matter collide, the matter could give off light that might be detected, particularly now that the observatories can better point to area of sky to search.
The LIGO observatories were shut down after the last operating run for work that will increase their sensitivity.
A short engineering run to test instruments as they run simultaneously may be conducted in December, followed by a second engineering run in March.
The Hanford and Lousiana LIGOs, along with Virgo in Italy, could start a year-long observation run as soon as April. Before the run is completed, Japan could add a fourth gravitational observatory, the Kamioka Gravitational Wave Detector, or KAGRA, to help search and provide additional information.
It will be the third observation run by LIGO Hanford since a major upgrade resulted in its first detection of gravitational waves.
“We’re really excited,” Landry said. “We could conceivably see a binary black hole every few weeks.”
The LIGO observatories look for the distortion as gravitational waves create ripples through the fabric of space and time, stretching space in one direction and contracting it in another. The waves turn a circle into an ellipse.
At the Hanford observatory two vacuum tubes extend for 2.5 miles across the Hanford shrub steppe landscape 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.
LIGO Hanford opens monthly for public tours, with the next tour set for Saturday. Outdoor walking tours will be held at 1:30 and 3:30 p.m., with a talk given in the LIGO auditorium for both tour groups at 3 p.m. No reservations are required.
To reach LIGO from the Tri-Cities, take Highway 240 to Hanford Route 10 — which is between mileposts 20 and 21 — and then drive north for about 5.5 miles.