A team of international gravitational wave astronomers has detected the most massive and most distant black hole collision recorded till date.
This is the first time that a collision leading to the formation of a black hole, which is 142 times heavier than the Sun, has been discovered by collaborators of Laser Interferometer Gravitational wave Observatory (LIGO) and VIRGO interferometer, located in Italy.
India is building the third of the LIGO observatories at Hingoli in Maharashtra.
A gravitational wave signal lasting 0.1 second emanated when black holes weighing 85 times and 66 times of solar mass, respectively, collided in a binary system. This newly- formed black hole, GW190521, then sent out a gravitational wave which travelled a distance of 17.2 billion light years, and was captured by detectors LIGO and VIRGO on May 21, 2019.
This is the most distant gravitational wave signal observed so far by the gravitational wave detectors.
Black holes, formed when massive stars collapse and die, is an invisible space located in the centre of the galaxy. It is packed with huge amounts of matter fused into a relatively small space. So far, two types of black holes — stellar and supermassive — have been discovered. A stellar blackhole weighs up to a 100 times more than the Sun, whereas a supermassive blackhole can have a mass of over one million times of the solar mass.
Theoretically, black holes with mass ranging between 100 to 1 lakh solar mass are termed as Intermediate Mass Black holes. This discovery gives the first direct observation of such black holes in the gravitational wave window.
“Black holes with masses ranging between 65 – 120 solar mass cannot be formed by a collapsing star as massive stars are highly unstable. However, an 85 solar mass black hole in this binary system suggests a newer possibility of black hole formation. For example, black holes merged by several collisions of smaller black holes in a globular cluster or galactic center,” said Professor Archana Pai from IIT-Bombay, one of the leading scientists involved in the discovery, published in the Physical Review Letters and the Astrophysical Journal Letters on Wednesday.
What adds to the significance of this extraordinary pair of stellar mass merger is the fact that this collision has been detected at the farthest distance so far.
The first gravitational waves detected by LIGO, in 2016, emerged from black hole collision that happened at a distance of 1.6 billion light years away. In this case, the signals have travelled from 17.2 billion light years away.
“The detectors captured signals even in the low-frequency range, essentially allowing scientists to travel further back into the history of the formation of the universe. This has been possible mainly due to the enhanced sensitivity of the gravitational wave detectors LIGO and VIRGO,” said Sanjit Mitra, senior scientist at Inter University Centre for Astronomy and Astrophysics (IUCAA), Pune.
This discovery is really exciting as it offers a line of new interpretation in astrophysics, IUCAA director Dr Somak Raychaudhury told The Indian Express. “There have been a few people who have been saying super massive black holes at the centres of galaxies are formed due to the merger of little ones, and now there is evidence,” said Dr Raychaudhury.
“It took 17 billion light years for this signal to travel through space and arrive in an uncorrupted state,” senior professor at IUCAA, Dr Sukanta Bose, told The Indian Express.
“Gravitational waves interact weakly with intervening matter. Since the signals are mostly unaffected by anything lying in its path — this allows us to understand the emitter or the source in a very precise manner,” said Dr Bose.
“The fact that such mergers are ubiquitous tells us how many large massive stars there are in the cosmos, which in turn produce heavy elements in the universe – some of them find their way into the human body,” said Dr Bose.
Scientists are hopeful about more discoveries of such intermediary black holes in the coming years using LIGO-India, which will add to the overall sensitivity of the detector.
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