"Mystery of Our Cosmos Deepens" --4th Detection of Gravitational Waves from a Cataclysmic Collision of Black Holes (WATCH Video)
Astronomers have made a new detection of gravitational waves, named GW170814, after the day it was detected, that occurred nearly 2 billion years ago, and for the first time have been able to trace the shape of spacetime ripples sent when black holes collide. The announcement, made at a meeting of the G7 science ministers in Turin, Italy marks the fourth discovery of cataclysmic black-hole merger, and the first to have also been picked up by the Virgo detector, located near Pisa, Italy, reveals a new layer of detail on the three dimensional pattern of warping that occurs during the violent collisions of black holes.
Virgo rejoined the hunt this year on 1 August, following a 5-year, €23-million (US$27-million) upgrade. And on 14 August, both it and LIGO picked up the gravitational vibrations emanating from a pair of rotating black holes, with masses of 31 and 25 times that of the Sun, as they merged together, physicists announced on 27 September at a press conference in Turin, Italy. The collision happened around 540 million parsecs (1.8 billion light years) away in the direction of the constellation Eridanus.
The wave arrived first at LIGO’s station in Livingston, Louisiana, as a ripple in space-time that subtly shifted the relative lengths of two arms of the detector as it passed. Just eight milliseconds afterward, the same wave swept past LIGO’s second detector in Hanford, Washington, before arriving at the Virgo detector six milliseconds later.
"It is tantalising to see this new story of how black holes formed and evolved through history of the cosmos," Sheila Rowan of Glasgow University told BBC News. "This information is almost within our grasp but we are not quite there yet."
The latest detection was the first to include the VIRGO detector and so the first for which astronomers could swing their telescopes into a more focused search zone. Giovanni Losurdo, who led the VIRGO project to completion, describing the inclusion of the Italian based-detector as a "milestone," said "The whole enterprise was based, since its start, on a visionary goal: the creation of a network capable of localising the sources in the sky and to start the era of investigation of the Universe. And finally, after decades, we are there."
The new data appears to strongly favor Einstein’s predictions of how spacetime is expected to be stretched and squeezed. Combining results from three detectors has also allowed scientists to more accurately triangulate the area of sky from which the waves are emanating. In future, this could allow scientists to swing ground-based telescopes to the target locations to see whether there is any visible trace of the collision itself.
“This was a very strong first," said Dr John Veitch, of the University of Glasgow, who co-led a team working on determining the origins and properties of the source. "Having a third detector means that we can now triangulate the position of the source, and much more accurately determine the exact spot in the cosmos where the signal came from.”
Having three detectors, according to Nature.com, enables researchers to make a rough measurement of the wave’s polarization — a property that describes how the wave propagates through space in three dimensions. This meant physicists could test a prediction made by Albert Einstein’s theory of relativity, which, besides predicting gravitational waves, also implies that such waves should stretch and contract space in planes that lie at right angles to each other.
The data from GW170814 seem to support this, Frédérique Marion, a physicist at the Laboratory of Particle Physics in Annecy-Le-Vieux, France and member of the Virgo Collaboration, told journalists at the press conference. “This was the first opportunity to check this fundamental property of gravitational waves,” she said.
In the case of black holes, reports The Guardian, theory predicts that there should be no optical signal – but astronomers are open-minded. “They should be dark ... but black holes are a mystery still to some extent,” said Freise. “We’re only getting signals from them for the first time, the rest is just theory.”
“This is just the beginning of observations with the network enabled by Virgo and LIGO working together. With the next observing run planned for late 2018, we can expect such detections weekly or even more often,” says David Shoemaker, a physicist at the Massachusetts Institute of Technology in Cambridge and spokesperson for the LIGO collaboration.
With three detectors, physicists can be more precise about the wave's origin than was possible before. On the basis of the time that Earth’s detectors received the signal, the teams triangulated the likely location of the source, whittling it down to a patch of sky that, as seen from Earth, appears about 300 times the size of the full Moon. That region is more than 10 times smaller than LIGO has managed to pinpoint for its previous sightings.
Image credit: LIGO