Gravitational Waves Have Officially Been Detected Again

Scientists from the LIGO Scientific Collaboration and the VIRGO collaboration have announced in a press conference the detection of gravitational waves from merging black holes for the fourth time. However, this time it was seen by three observatories.

The two black holes that merged are located 1.7 billion light-years away, with a mass of 30.5 and 25.3 times the mass of the Sun, respectively. This discovery has been reported in the journal Physical Review Letters.

“This is just the beginning of observations with the network enabled by Virgo and LIGO working together,” says David Shoemaker of MIT, LSC spokesperson, in a statement. “With the next observing run planned for Fall 2018 we can expect such detections weekly or even more often.”

The use of three detectors has also allowed astronomers to significantly constrain the area in the sky where these objects might originate from. However, since they don’t emit light, no optical counterpart was observed with telescopes.

The merger was detected on August 14, and it marks the first time that three gravitational wave observatories have detected the same event. The previous three detections of gravitational waves were only observed by the two LIGO detectors, one located in Washington State and the other in Louisiana. The VIRGO detector has been receiving an important upgrade, and only joined the other two on August 1, just in time to spot this cosmic collision.

“Little more than a year and a half ago, NSF announced that its Laser Gravitational-Wave Observatory had made the first-ever detection of gravitational waves resulting from the collision of two black holes in a galaxy a billion light-years away,” said France Córdova, NSF director. “Today, we are delighted to announce the first discovery made in partnership between the Virgo Gravitational-Wave Observatory and the LIGO Scientific Collaboration, the first time a gravitational-wave detection was observed by these observatories, located thousands of miles apart. This is an exciting milestone in the growing international scientific effort to unlock the extraordinary mysteries of our Universe.”

The event, known as GW170814, is an important contribution to the science of gravitational waves. With every black hole collision we detect, we expand our understanding of these complex objects. Gravitational waves provide the only direct observation of black holes and they allow researchers to test their theories against what we see, including a new test for general relativity. The observations let physicists test the polarization of gravitational waves, which reveal how changes in space-time happen as these waves travel through the universe. GW170814 has helped reduce the possible hypotheses.

LIGO and VIRGO are laser interferometer detectors, and each facility is L-shaped with lasers sent down tunnels to reflect on mirrors and back into the detector to be compared to the original emission. If a gravitational wave passes through, it will change how the reconstructed beam looks. The announcement was given on the eve of the G7 of Science Ministers that takes place in Turin, Italy, on September 27 and 28. Representatives of both scientific collaborations were present at the conference.

The detectors will be now be tuned and upgraded over the next year in the hopes of improving the sensitivity of the instruments by a factor of 2.

Location of the signal. LIGO