The existence of gravitational waves has been detected for the first time, 100 years after Albert Einstein predicted their existence in 1916.
Two black holes that collided 1.3 billion years ago created the waves seen at a new type of space observatory, one located at Hanford in Washington state and the other in Louisiana, officials announced Thursday morning.
“Ladies and gentlemen, we have detected gravitational waves. We did it!” said David Reitze, a physicist and executive director of the LIGO Scientific Collaboration. “I am so pleased to be able to tell you that.”
Violent events in space, like the collision of black holes, the explosion of stars or changes in the speed or direction of large objects create gravitational waves, or ripples through space and time.
The National Science Foundation has been working toward the detection of a gravitational wave for 40 years, spending about $1 billion to date. It was a major gamble, scientists said. But with a potentially huge payoff.
It is mind-boggling.
David Reitze, physicist
The discovery confirms Einstein’s theory of relativity. It’s the first time two black holes have been observed orbiting each other and then colliding.
But what’s exciting to scientists is what comes next.
“It is the first time the universe has spoken to us through gravitational waves,” Reitze said.
Detection of gravitational waves 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.
“It’s mind-boggling,” Reitze said.
The Laser Interferometer Gravitational-wave Observatory at Hanford and its twin in Louisiana operated from 2002 to 2010 without detecting a wave.
The next five years were spent on a complete overhaul and update of the observatories, giving them the capability to be 10 times more sensitive.
In August 2015 the observatories started some initial engineering runs to test equipment and prepare for the official start of observations Sept. 18.
But at 2:50 a.m. Sept. 14 at the Hanford LIGO, an unusual reading was recorded. Just seven-thousands of a second earlier a similar reading had been recorded at the Louisiana LIGO.
It looked perfect, said Fred Raab, the head of LIGO at Hanford. “I knew it had to be real.”
Now he knows how it must feel to win the lottery, he said.
“It was a moment of amazement,” he said. “Then you are thinking, ‘Can this really be true?’”
There was a suspicion that the reading was one of the blind, false signals injected into data to test sensitivity of analysis techniques.
But Raab was one of the few scientists who knew that was not the case. Getting the data injections set up was one of the final steps that still needed to be done before the official start of observations.
Gravitational waves carry huge amounts of energy, but dissipate to the point that they are barely detectable once they pass through Earth.
With a possible detection, the settings were frozen for the next 38 days by the LIGOs in both states to collect background data to make certain the reading had not been statistical noise.
Even though the upgraded LIGOs are still well below their designed sensitivity, the data collected exceeded all the data they collected in their first decade of operation by volume of space and time covered, Raab said.
The gravitational wave detected was powerful — “loud” according to the language the scientists use — but it still would not have been heard before the upgrade.
The waves carry huge amounts of energy, but dissipate to the point that they are barely detectable as they pass through Earth.
As the waves move through objects, they stretch them lengthwise and cause them to compress sideways. A circle would become an ellipse.
The change is so small that it takes LIGO, the most precise measuring device ever built, to detect it.
The movement is about one thousandth of a diameter of a proton, which is the nucleus of a hydrogen atom. It would take 10 trillion such movements to equal the width of a human hair.
LIGO is a new type of observatory with no telescope required.
Two vacuum tubes extend for 2.5 miles across the Hanford shrub steppe 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 gravity wave is pulsing through the Earth, making one of the tubes slightly longer and the other slightly shorter, the beam will not recombine as expected.
Scientists watching for a gravitational wave also detect movement caused by many other things. They have to sort through vibrations caused by ocean waves on the Pacific Coast or water coming over McNary Dam in the spring.
That’s why there’s a twin facility. Findings at LIGO at Hanford can be compared with an identical LIGO 1,900 miles away in Louisiana. If a gravity wave passes through Earth, both LIGOs should detect it.
When the graph of the detection of the wave in Louisiana is overlaid with the graph from the Hanford detection, they match nearly perfectly.
It looks just as predicted by Einstein.
Scientists believe that the two black holes in the event were about 29 and 36 times the mass of the sun. About three times the mass of the sun was converted into gravitational waves in a fraction of a second.
“This is the most powerful event ever detected by humans,” said Jenne Driggers, a post-doctoral researcher at the Hanford LIGO. “It is enormous and exotic and amazing.”
The peak power output was about 50 times that of the whole visible universe.
Because the wave arrived at Louisiana first, scientists can say the wave moved through the Earth from south to north.
Being able to detect and measure waves should advance knowledge of astronomy and physics. New information on the nature of time and space and the creation of the universe could be revealed.
Scientists are going to test general relativity with increasing observations of binary black holes, said Mike Landry, the Hanford LIGO lead detection scientist. Perhaps information will be revealed about their origin.
“We’ve turned on a new type of instrument,” he said. “There’s a real possibility we could get a surprise. That would be frankly the most interesting thing that could happen with a new instrument.”
Scientists are hoping to see gravitational waves from sources not imagined now.
More discoveries could be coming from the observations just completed.
Raab is not saying what other intriguing data may have been collected from the initial run of the upgraded LIGO. But there is at least a possibility of another gravitational wave detection. Only slightly more than a third of the data from the first run has been analyzed.
LIGO public celebration
Tour the LIGO Hanford gravitational wave observatory site and hear talks by scientists March 12. Arrive at 11 a.m., 12:30 p.m., 2 p.m., 3 :30 p.m. or 5 p.m. Email firstname.lastname@example.org with your preferred time, an alternate time, the number of people in your party and the license plate of the car arriving at LIGO. An email admission ticket will be emailed to you.
LIGO Hanford is at 127124 N. Route 10 outside Richland. Find driving directions by clicking here: https://www.ligo.caltech.edu/WA/page/lho-driving-directions