4th gravitational wave detected with help from Indian scientists

Originally predicted in the early 20th century by Albert Einstein, gravitational waves were not detected until 2015

Scientists have detected the fourth gravitational wave emitted by a merger of two black holes using three detectors — a critical new capability that allows scientists to more closely locate a gravitational wave's birthplace in space.

The collision was observed using two Laser Interferometer Gravitational-wave Observatory (LIGO) detectors located in the US — in Livingston, Louisiana, and Hanford, Washington — and the Virgo detector in Italy.

"Virgo adds new capability to the LIGO network. Thanks to Virgo we can now test a key prediction of Einstein's general relativity, namely the polarisation property of the wave," said B S Sathyaprakash, Professor at Pennsylvania State University.

"The two LIGO detectors alone are not able to infer the polarization property of gravitational waves because they alone could not fix the position of the source in the sky. The addition of Virgo as a third detector helps in localizing the source and hence allows us to infer the wave's polarization. As far as we can tell, Einstein is still right," Sathyaprakash said.

Originally predicted in the early 20th century by Albert Einstein, gravitational waves — ripples in space and time — were not detected until 2015, when LIGO identified the first such signal from two merging black holes.

LIGO's two detectors later detected two other similar events.

The latest event observed on August 14, 2017, will be detailed in a forthcoming issue of the journal Physical Review Letters.

"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," said France Cordova, Director of the US National Science Foundation, which funded the LIGO project.

"This is an exciting milestone in the growing international scientific effort to unlock the extraordinary mysteries of our universe," Cordova added.

The detected gravitational waves were emitted during the final moments of the merger of two black holes with masses about 31 and 25 times the mass of the Sun and located about 1.8 billion light years away, researchers said.

The newly produced spinning black hole has about 53 times the mass of our Sun, which means that about three solar masses were converted into gravitational wave energy during the coalescence, they said.

The Virgo collaboration, which joined in the LIGO's observation on August 1, consists of more than 280 physicists and engineers belonging to 20 different European research groups.

India is also working towards setting up its own LIGO observatory.

The move received in-principle approval from the cabinet in February last year and has made rapid progress towards the plan to join these exciting scientific observations in 2024.

LIGO-India will greatly enhance the scientific capabilities of the international network of observatories for astronomy, primarily by enabling precise pointing to the location of the gravitational wave events in the sky.

Scientific and engineering teams at IPR Gandhinagar, IUCAA Pune and RRCAT Indore are actively engaged in the pre-construction activities of LIGO-India.