Researchers from the Indian Institute of Astrophysics, Bengaluru, have observed three supermassive black holes from three galaxies merging to form a triple active galactic nuclei, using data from India’s only astronomy space mission, Astrosat.
“Our study found that there are three galaxies, each with an active galactic nucleus forming a triple AGN system. Cosmological modelling predicts that there should be 16% triple AGN but only a handful have been observed so far,” said Jyoti Yadav, the lead author of the correspondence in journal Astronomy and Astrophysics. So far, researchers have only observed five triple active galatic nucleus (AGN).
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It is difficult to detect supermassive black holes as they do not emit any light. However, the black holes become luminous when, upon interaction with their surroundings, they swallow dust and gases, converting it into electromagnetic radiation.
The researchers suggest that merging galaxies are the ideal laboratories for detecting multiple supermassive black holes. “We generally expect that every galaxy has a black hole but we do not see it. But it can be observed by studying galaxies interacting, when the gases move towards the central part of the galaxy and trigger the AGN activity. We expect multiple AGNs in interacting galaxy groups,” said Yadav.
The researchers were studying a pair of known galaxies — NGC7733 and NGC7734 — when they detected an unusual bright clump at the centre of one of them. The clump, however, was moving at a different velocity compared to the one in which it was observed, the researchers said. This, the researchers said, meant that the clump was not part of the same galaxy but rather a small separate galaxy that they named NGC7733N.
“Sometimes when two galaxies apply force on each other, some of the matter can be stripped out of the galaxies. If this matter is enough, it can collapse under its own gravity and form a single small galaxy,” said Yadav.
The researchers – also including Mousumi Das and Sudhanshu Barway from IIA, Francoise Combes from College de France and Chaire Galaxies et Cosmologie-Paris — used data from Astrosat, which was launched by the Indian Space Research Organisation in 2015, the Infrared Survey Facility in South Africa and spectroscopic data from MUSE (Multi Unit Spectroscopic Explorer) in Chile.
Yadav said that understanding the evolution of galaxies is necessary to understand the evolution of the universe. “Currently, we do not understand how the gases reach the inner parsec (parsec is a unit of length to measure large distances to astronomical objects outside the solar system) region of the galaxy. AGNs also affect the evolution of the galaxies; if we want to study the evolution of the universe we should know how the galaxies evolve. An AGN sitting in the centre of the galaxy can release huge amounts of energy that can start the star formation by pushing gas or stop it by removing gas from the galaxy,” she said.