Indian scientists spot rare merger of three big black holes

Indian scientists have discovered the merger of three supermassive black holes from as many galaxies to form a triple active galactic nucleus, the Department of Science and Technology said on Friday. The block holes are forming the nucleus, which is a compact region at the centre of a new galaxy with much higher-than-normal luminosity. 

The DST said, “Supermassive black holes are difficult to detect because they do not emit any light. But they can reveal their presence by interacting with their surroundings."

Such small mergers are ideal to detect multiple accreting supermassive black holes, as they do not emit any light. Thus, these merging activities also increase the possibility of detecting such rare occurrences. 

A team of astrophysicists was studying NGC7733 and NGC7734, a known interacting galaxy pair, when they detected unusual emission from the centre of the latter while a large, bright clump along the northern arm of the former. The clump was moving with a different velocity compared to the galaxy NGC7733.

After further investigation by researchers, from the Indian Institute of Astrophysics consisting of Jyoti Yadav, Mousumi Das, and Sudhanshu Barway along with Francoise Combes of College de France, Chaire Galaxies et Cosmologie, Paris, they discovered it was a small, separate galaxy behind the arm and named it, NGC7733N. 

“The scientists meant that this clump was not a part of NGC7733; rather, it was a small separate galaxy behind the arm. They named this galaxy NGC7733N,” the DST said.

The study was published in the journal Astronomy and Astrophysics. Researchers used data from the Ultra-Violet Imaging Telescope (UVIT) onboard the first Indian space observatory ASTROSAT, the European integral field optical telescope called MUSE mounted on the Very Large Telescope (VLT) in Chile and infrared images from the optical telescope (IRSF) in South Africa to conduct the study, news agency PTI reported.

The study said that UV and H-alpha images also supported the presence of the third galaxy, which was revealed by star formation along with tidal tails that could have been formed from the merger of NGC7733N with the larger galaxy.