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New Delhi: In what can be described as another major milestone towards detection of gravitational waves, scientists on Thursday announced that a fourth detection of gravitational waves has been made.

This time, the LIGO (Laser Interferometer Gravitational-Wave Observatory) was joined by the Virgo observatory from Europe, which significantly contributed to the improved localization of this astronomical source in the sky and enabled new tests of Einstein’s theory based on the polarization of gravitational waves, said an official statement from the Inter University Centre for Astronomy and Astrophysics (IUCAA), Pune.

Three detectors together delivered a significantly better localization of the source and access to polarizations of gravitational waves. This event, detected on 14 August 2017, is the fourth detection of a merging binary black hole system, the statement explained.

The Virgo detector in Italy started collecting data only on 1 August.

In February 2016, scientists at the US based LIGO announced detection of gravitational waves rising from the merger of two black holes 1.3 billion years ago.

The discovery, hailed as biggest scientific breakthrough in past many decades, opened a new chapter in human understanding of space and time and offering better insights into the origin of the universe and how planets are created. The discovery was made nearly 100 years after their existence was first predicted by Albert Einstein.

In simple terms, gravitational waves can be explained as ripples in the fabric of space-time which can only be caused by massive astronomical events such as neutron stars or black holes orbiting each other so that these waves would finally radiate from them.

These gravitational waves, if detected, will carry signatures of their origin, explaining much about the nature of gravity and the origin of the universe. They had remained elusive till their detection was first announced last year.

“This is the fourth detection of the black hole binary system. What is new this time compared to past detections is that this time there are three detectors and we could locate much better where in the sky this event happened," said Tarun Souradeep, who is LIGO’s India spokesperson.

Explaining further, ICUAA said that the signal was produced by the merger of two massive black holes, weighing 31 and 25 times the mass of the Sun at a distance of 1.7 billion light years away from us.

“An energy equivalent to the mass of three Suns was radiated as gravitational waves in this energetic astronomical event. These detections of gravitational waves from merging black hole pairs allow us to map out the distribution of black holes in the universe and to do precision tests of Einstein’s theory of General Relativity," IUCAA said.

The results from this detection are presented in a new scientific paper which has been accepted for publication in the journal Physical Review Letters.

Meanwhile, stressing that Indian scientists have done foundational work in various aspects of gravitational-wave science over the last three decades, IUCAA said that “the current Indian team in the LIGO-Virgo collaboration has made direct contributions to the extraction of the properties of the astronomical source from the data and to the first tests of Einstein’s theory using these observations."

The Indian contribution is expected to grow significantly in years ahead with the materialisation of the LIGO-India observatory, which is being built in the country.

Soon after the February 2016 discovery, Indian government had given in-principle approval to set up a detector in India. LIGO-India project is being piloted by the department of atomic energy and department of science and technology.

“There is a team of about 40 Indian scientists from 13 institutes across the country that is working within the international LIGO science collaboration. We are also working hard to get our own detector up as soon as possible. Its construction should be completed by 2022 and it should start science operations by 2024," added Tarun Souradeep.

LIGO is a system of two identical detectors located in Livingstone, Lousiana, and Hanford, Washington, which were constructed to detect tiny vibrations from passing gravitational waves. The instruments were designed and operated by the California Institute of Technology (Caltech) and the Massachusetts Institute of Technology (MIT), with funding from the National Science Foundation.

LIGO-Virgo collaboration includes more than a thousand scientists from many different countries, setting a great example in international scientific cooperation. While LIGO project includes 1200 scientists from across the world, the Virgo collaboration consists of more than 280 physicists and engineers belonging to 20 different European research groups.

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