Gravitational waves: Two black holes merge to become one, give food to LIGO to detect ripples predicted by Albert Einstein

The Laser Interferometer Gravitational-wave Observatory (LIGO) in the US comprising of scientists from across the world, including those from India, has announced that the team has yet again detected gravitational waves for the third time. The gravitational waves are the ripples in the space that were first predicted by Albert Einstein more than a century ago.

The detection of third gravitational waves was made by LIGO on January 4 this year. The detection has firmly opened a new window in astronomy. The extremely sensitive LIGO detectors can hear the gravitational waves as they pass though the Earth.

While the first gravitational waves were detected in September 2015 during the first observing run, a second detection was made in December 2015.

The latest gravitational waves detection has been described in a new paper accepted for publication in the journal Physical Review Letters. Just like the first two detections, the waves occurred when two black holes merged to form a larger black hole.

"Our handful of detections so far is revealing an intriguing black hole population we did not know existed until now," said Northwestern University's Vicky Kalogera, a senior astrophysicist with the LIGO Scientific Collaboration (LSC).The new gravitational wave detection is called GW170104. It took place during the ongoing second observing run of the Advanced LIGO detectors which began on November 30, 2016.

40 authors in the publication belong to 11 Indian institutions. Under the leadership of Dr Chandra Kant Mishra, IIT-Madras recently joined the LSC as one of the participating institutes. Led by Dr K.G. Arun, the Chennai Mathematical Institute has also been contributing to the activities.

The IIT-Madras team models the sources of the gravitational wave such as the ones detected by the LIGO detectors so far. They also test the consistency of the detected gravitational wave signals with the predictions of Einstein's general theory of relativity.

The latest detection of gravitational waves shows how the black holes located twice as far away from Earth as the two earlier pairs – about three billion light-years away – merge.

This time around, the size of the two black holes was different with one significantly lighter than the other. They merged and formed a black hole whose size is in the middle of the other two merged black hole pairs.

"Now we have three pairs of black holes, each pair ending their death spiral dance over millions or billions of years in some of the most powerful explosions in the universe. In astronomy, we say with three objects of the same type you have a class. We have a population, and we can do analysis," Kalogera added.

The newly formed black hole has a mass of about 49 times that of our sun. This fills in a gap between the masses of the two merged black holes that were previously detected by LIGO. They had solar masses of 62 (first detection) and 21 (second detection).

"We have further confirmation of the existence of black holes that are heavier than 20 solar masses, objects we didn't know existed before LIGO detected them," said David Shoemaker of MIT, the newly elected spokesperson for the LSC.

India is also working towards setting up of its own LIGO observatory and the move had received approval from the cabinet in February last year. The LIGO observatory in India once set up will greatly enhance the scientific capabilities of the international network of observatories for astronomy.

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

India’s contribution in gravitational waves detection:

ALSO READ | China building Gravitational waves observatory worth $18.8 million close to border with India

India’s strong efforts have been involved in these detections that were made by contribution from researchers from across the world. The scientists from India have performed foundational work over the last three decades in modelling the signal waveforms and developing mathematical techniques to search for gravitational wave signals in noisy data.

"With the third definite detection of from a coalescing black hole binary, we have discovered a new class of astrophysical sources to test Einstein's theory of general relativity in extreme conditions," Bala Iyer, the Principal Investigator of the Indian team in LIGO said.

ALSO READ | Albert Einstein Institute's scientist terms gravitational waves detection as most important scientific discovery of 2015