Black holes are created when a massive star collapses and dies. When two black holes are in orbit in a binary system, they send out gravitational waves and lose energy. When they approach, they collide, resulting in a large gravitational wave signal. The scientists of these two institutes determined this signal from the collision of two massive black holes with the help of data from the Laser Interferometer Gravitational Wave Observatory (LIGO) in the USA and the VIRGO detector in Italy as part of the international LIGO Scientific Collaboration, consisting of over 15 countries .
The collision occurred about 17.5 billion light years ago, and the signals traveled to Earth and were discovered on May 21, 2019. “It took us a year to understand and study the data and rule out fake signals,” said Anand Sengupta from the Faculty of Physics at IIT-Gandhinagar. The gravitational wave discovered by the researchers was named GW190521 and is believed to have originated from the formation of what theorists call a medium-mass black hole. The results of their findings were published this week in Physical Review Letters and The Astrophysical Journal Letters.
Black holes are divided into three types, explained Archana Pai, a researcher from the physics department at IIT-Bombay. “The black hole with stellar mass less than 100 solar masses (one solar mass is the mass of our sun), the supermassive black holes that weigh 10 lakh solar mass and more, and the third was the medium-mass black hole – which is located between these two. This particular black hole of 142 solar masses was the result of a collision between two black holes weighing 85 and 66 solar masses, which is an interesting event in gravitational wave astronomy due to the remnant of the intermediate mass black hole itself, Pai said. While black hole collisions were previously spotted by LIGO and Virgo detectors, such a massive and age-old collision has never been seen, she said.
“The results of this massive black hole system have raised further questions about the formation of these massive black holes, which could likely be the culmination of a collision of black holes with smaller stellar mass,” said Pai. “The medium-mass black holes are considered to be the building blocks of supermassive black holes. This is also an advance in studying supermassive black holes, ”she added. Pai was accompanied by her PhD student Koustav Chandra during the research.
The heavier the system, the shorter its duration in the sensitive bandwidth of the LIGO detector, making it more difficult to study such signals, Sengupta said. “These systems are far from us, so the signals are very weak. We have to use various techniques to comb through the data and compare it with the theoretical models of the black holes known to us. It took us a year to confirm our results, ”said Sengupta.
He said that fundamental contributions to their research come from extensive contributions by the LIGO India team from various institutes in the country including IUCAA Pune, IISER Kolkata, Pune, ICTS Bengaluru, TIFR Mumbai, etc. Sengupta said the exciting thing is the detection of the first black hole of medium mass derived from other optical observations, but not by detection of gravitational waves. It is a major breakthrough in astrophysics observation, he added.