Third time's a charm: LIGO detects gravitational waves for a third time

In all three cases, the gravitational waves came from the tremendous energy produced by two merging black holes. This third detection was of a pair of "intermediate" black holes 19 to 31 times the size of the sun.

Gravitational waves are ripples in the spacetime that travel at the speed of light. The third detection, called GW170104 and made January 4, 2017, is described in a new paper accepted for publication in the journal Physical Review Letters.

The newly detected merger occurred approximately 3 billion years ago, making it more than twice as old (and more than twice as distant) as the first two events, which occurred 1.3 and 1.4 billion years ago, respectively.

The detectors are a pair of big instruments in Hanford, Wash., and Livingston, La., and the discovery was heralded as a triumph for the 1,000 physicists with the Laser Interferometer Gravitational-Wave Observatory (LIGO) in Livingston. All of them are more massive than the black holes that astronomers had previously identified as the remnants of dead stars.

An worldwide scientific collaboration project, LIGO consists of two detectors, one in Hansford, Washington, and the other in Livingston, Louisiana. LIGO has not found any evidence of dispersion in gravitational waves, as predicted by relativity. But if that's the case, that means that it's possible for heavy stars to create large black holes - which flies in the face of existing astronomical theory.

LIGO picked up the latest space-time ripple on January 4 of this year, quickly determining that the collision occurred an astonishing 3 billion light years away, meaning that the vibrations had been travelling for 3 billion years before reaching LIGO's instruments on our pale blue dot.

After a journey lasting three billion years, those waves started jiggling Ligo's mirrors back and forth by a fraction of an atomic diameter 20 times a second. These ripples in the fabric of space and time, caused by a black-hole collision some 1.3 light years from Earth, provided the first concrete evidence of a phenomenon first proposed by Albert Einstein in 1916 in his theory of general relativity.

As with the first two detections, the waves were generated when two black holes merged to form a larger black hole.

"We have further confirmation of the existence of stellar-mass black holes that are larger than 20 solar masses - these are objects we didn't know existed before LIGO detected them", said David Shoemaker, spokesperson for the LIGO Scientific Collaboration (LSC), a body of more than 1,000 worldwide scientists.

The new observation occurred during LIGO's current observing run, which began November 30, 2016, and will continue through the summer. "We're conducting a census of black holes in binary systems in our universe and we expect to discover other types of signals too". "Different teams have made different predictions for black hole spins".

RIT scientists helped the collaboration measure and interpret black hole spins and their alignment.

The GW170104 event also provides clues about the directions in which the black holes are spinning.

"It looks like Einstein was right - even for this new event, which is about two times farther away than our first detection", Georgia Tech's Laura Cadonati, the Deputy Spokesperson of the LIGO Scientific Collaboration (LSC), said in the press release.

The LIGO Laboratory receives funding from the National Science Foundation (NSF) and is operated by Caltech and MIT, which conceived and built the observatory. They are also working on substantial technical upgrades for LIGO's third run, scheduled to begin in late 2018, with help from the almost completed Virgo detector in Italy collecting data simultaneously.

More than 1,000 scientists and engineers from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. LIGO partners with the Virgo Collaboration, a consortium including 280 additional scientists throughout Europe supported by the Centre National de la Recherche Scientifique (CNRS), the Istituto Nazionale di Fisica Nucleare (INFN), and Nikhef, as well as Virgo's host institution, the European Gravitational Observatory.

  • Carolyn Briggs