In a major breakthrough, Indian researchers have discovered three supermassive black holes merging together to form a triple active galactic nucleus. The black holes have been spotted at the centre of a recently discovered galaxy that increases the possibility of further detecting such rare occurrences.
The study published as a letter in the journal Astronomy and Astrophysics was intended to investigate the nature of the nuclear emission from the galaxies in the interacting pair NGC 7733NGC 7734.
“We have confirmed the existence of the third galaxy, NGC 7733N, in the NGC 773334 group. It appears to overlap with the northern arm of NGC 7733,” researchers said in the paper.
Discovering triple merging galaxy
A team of researchers from the Indian Institute of Astrophysics came upon the rare occurrence while studying a known interacting galaxy pair, NGC7733, and NGC7734. The researchers detected unusual emissions from the centre of NGC7734 and a large, bright clump along the northern arm of NGC7733. As they dug deeper, they found that the clump is moving with a different velocity compared to the galaxy NGC7733 itself indicating that it was not part of the galaxy instead it was a small separate galaxy behind the arm.
Led by a team comprising Jyoti Yadav, Mousumi Das, and Sudhanshu Barway from the Indian Institute of 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.
“The UV and H-alpha images also supported the presence of the third galaxy by revealing star formation along with the tidal tails, which could have formed from the merger of NGC7733N with the larger galaxy,” researchers said in a statement.
The third galaxy seen in inset. (Photo: Astronomy & Astrophysics)
Merger of galaxies
Interaction of galaxies and mergers are the major drivers of galaxy evolution leading to the growth of supermassive black hole bulges and massive galaxies. “One of the most favourable environments for such activity are galaxy groups where galaxies are closely interacting, especially those that have significant reservoirs of cold gas that can be used to fuel star formation and active galactic nuclear (AGN) activity,” researchers said in the paper.
Interaction of galaxies begins when they come close and exert tremendous gravitational forces on each other, during which, the respective supermassive black holes can get further close and the dual black holes start consuming gas from their surroundings and become dual AGN.
“Galaxy interactions can also lead to triple merger systems, and if the SMBHs of the individual galaxies are accreting, a triple-AGN system will form,” the paper said.
What happens when the two galaxies collide?
The IIA team explains that if the two galaxies collide, their black hole will also come closer by transferring the kinetic energy to the surrounding gas. The distance between the black holes decreases with time until the separation is around a parsec (3.26 light-years).
This is how a black hole looks. (Photo: Nasa)
The two black holes are then unable to lose any further kinetic energy in order to get even closer and merge. This is known as the final parsec problem. The presence of a third black hole can solve this problem. The dual merging black holes can transfer their energy to the third blackhole and merge with each other.
Recently scientists had proven Stephen Hawking’s theory surrounding black holes, which states that it is impossible for a black hole to decrease in size over time. The theorem has been derived from Albert Einstein’s theory of relativity that defines gravitational waves and black holes.
What is a black hole?
A black hole is formed from the death of a star with such a high gravitational field that the matter gets squeezed into the small space under it, trapping the light of the dead star. The gravity is so strong due to the matter being squeezed into a tiny space. Since no light can get out, people can’t see black holes. They are invisible.
Researchers had recently detected light behind a black hole for the first time, contrary to the scientific theory that the immense dark void does not even allow light to pass through. Researchers spotted bright X-Ray flares emerging from a supermassive black hole at the centre of another galaxy, which is nearly 800 million light-years away.