Update, 10:50 a.m.:
For the first time, scientists have observed ripples in the fabric of space and time, called gravitation waves, confirming a major prediction of Albert Einstein's 1915 general theory of relativity and opening an unprecedented new window into the cosmos.
The announcement was made Thursday by scientists with the Laser Interferometer Gravitational-wave Observatory, or LIGO.
The gravitiation waves were detected at 4:51 a.m. on Sept. 14, 2015, by both of the twin LIGO detectors in Livingston, La. and Hanford, Wash.
"For a long time, the O in LIGO was a wish, but as of now, it is no longer a wish. We observed something," said Joe Giaime, head of the Livingston observatory.
Gravitational waves carry information about their origins and about the nature of gravity that cannot otherwise be obtained, LIGO scientists said. Physicists concluded that the detected waves were produced during the merger of two black holes to produce a single, massive black hole. This collision of two black holes had been predicted but never observed.
On Sept. 14, the LIGO instrument in Livingston, followed 7 milliseconds later by the instrument in Hanford, detected a gravitation wave signal from colliding black holes. The near simultaneous detection was necessary to confirm the event was real, scientists said, and indicated based on the relative time of arrival of the signals traveling at the speed of light that the source was in the southern hemisphere sky.
Based on the physics of this particular event, LIGO scientists estimate the two black holes in this event were about 29 and 36 times the mass of the sun, and that the event took place 1.3 billion years ago.
"This is just the beginning. Now that we know these signals are out there, we are only beginning to listen to the universe," said Gabriela Gonzalez, spokeswoman for the LIGO Scientific Collaboration.
Thursday's announcement was hailed by scientists as a major breakthrough. Renowned physicist Stephen Hawking called the news "thrilling" and posted his congratulations to the LIGO team on Facebook:
The rumors started swirling almost as soon as the observatories in Livingston Parish and Washington state began collecting data with their upgraded equipment in September: LIGO scientists had detected gravitational waves.
If true, the discovery would prove Albert Einstein’s general theory of relativity — on the centennial of its publication, no less — and be the odds-on favorite for the Nobel Prize in Physics, experts say.
Officials at the Laser Interferometer Gravitational-wave Observatory have coyly avoided confirming or denying the rumors. But the speculation reached a fevered pitch late last week, when a Canadian physics professor’s email detailing LIGO’s possible detection of gravitational waves from the merger of two black holes was published online.
LIGO officials will break their silence Thursday morning, when they hold a news conference at the National Press Club in Washington, D.C. Their European partners from the VIRGO Collaboration will hold a simultaneous news conference at the European Gravitational Observatory in Cascina, Pisa, Italy.
Gravitational waves are distortions, or ripples, in the fabric of space-time caused by violent and energetic processes like colliding black holes, the collapse of stellar cores into supernovae or the birth of the universe itself, said Gabriela González, LSU professor of physics and astronomy and spokeswoman for the LIGO Scientific Collaboration.
The ripples travel through the universe at the speed of light, carrying with them information about the cataclysmic events that created them.
Scientists have indirectly observed gravitational waves in the past, using radio telescopes to show that the orbital decay of a pair of binary pulsars fit with Einstein’s predictions, but the waves have never been directly detected.
LIGO’s twin observatories in Livingston and Hanford, Washington, officially began their latest observation run — the first one following a five-year, $200 million equipment upgrade — on Sept. 18.
The upgrade involved changing out almost every part of the late-‘90s detector system, which looks for gravitational waves by measuring for variations in the time it takes a laser beam to travel down two perpendicular tubes that are two and a half miles long.
The new detector, known as Advanced LIGO, has the potential to be 10 times more powerful than its predecessor, said Joseph Giaime, head of the Livingston observatory and a professor of physics and astronomy at LSU.
Getting it there will take several rounds of commissioning, or fine-tuning, but the equipment already has become three to four times as sensitive, allowing them to see up to 240 million light years into space, compared to about 60 million light years before.
Despite the increased sensitivity, it was surprising to see rumors of a gravitational wave detection as early as one week after the upgraded equipment was officially put to work.
The scientists at LIGO had predicted they would detect gravitational waves from a binary neutron star system — the most likely and predictable of sources they were seeking — during this first run “only if the most optimistic astrophysical rates hold,” according to a paper the group published in advance of the work.
And yet, one week in, the gossip began.
“Rumor of a gravitational wave detection at LIGO detector,” well-known physicist and Arizona State University professor Lawrence Krauss tweeted on Sept. 25. “Amazing if true. Will post details if it survives.”
A few months later, on Jan. 11, the day before LIGO completed its observation run, Krauss tweeted an update: “My earlier rumor about LIGO has been confirmed by independent sources. Stay tuned! Gravitational waves may have been discovered!! Exciting.”
Pummeled by reporters seeking confirmation, Krauss clarified the next day, “A rumor is a RUMOR. LIGO will make any announcement if there is one.”
But, far from dying away, the rumor appeared to solidify into something incredibly specific last week, when Science Magazine published an email from Canadian physics professor Cliff Burgess, claiming “spies” who had seen LIGO’s forthcoming paper confirmed the detection of gravitational waves from a binary black hole merger.
“The bh (black hole) masses were 36 and 29 solar masses initially and 62 at the end,” Burgess wrote in an email intended only for members of his department. “Apparently the signal is spectacular and they even see the ring-down to kerr at the end. Woohoo! (I hope)”
Although less predictable than orbiting neutron stars, a merger of two black holes would create stronger gravitational waves that could be observed from much farther out, said Michael Cherry, chair of LSU’s Department of Physics and Astronomy.
“The most likely source (of gravitational waves) that has been expected for years was two orbiting neutron stars,” Cherry said. “We know systems like that exist... But if you have the capability to view farther out, you have a bigger volume of space you can look at, so a signal from a pair of black holes might be visible from farther than the distance of a pair of neutron stars.”
Giaime, the Livingston observatory director, said the group had “extraordinary good luck” in getting the advanced detector near the upper end of the sensitivity range expected for this observing run.
LIGO also “hit the ground running with our colleagues doing other work in the field,” Giaime said. “We were much more ready for multi-messenger astronomy this time.”
That collaborative work involves combining observations of a single event through different means, such as optical light, gamma emission and electromagnetic counterparts.
LIGO partners with dozens of observatories around the world who can scan the skies for those other pieces of information.
A recent examination by New Scientist Magazine revealed that one such observatory, the European Southern Observatory in Chile, was conducting searches for the bright flashes of light that can accompany gravitational wave signals during the same period as LIGO’s observing run and may have helped to spot three potential gravitational wave signals.
Krauss, whose tweets set off the flurry of rumors Thursday’s news conference will either confirm or dispel, seems optimistic about LIGO’s potential discovery.
“HAPPY that my tweet and resulting excitement likely not misplaced,” Krauss tweeted on Feb. 4. “LIGO WASH DC PRESS CONF., FEB. 11! GRAV WAVES & NEW ERA IN ASTRONOMY?!!”
If so, Giaime and his colleagues are keeping mum right down to the wire: “We’re pretty old-school. We write our papers, send them to journals, and only after it passes muster do we blab about it.”
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