The study has been published as a letter in the journal ‘Astronomy and Astrophysics’
A rare fusion of three supermassive black holes has been detected by a team of astrophysicists in India. They were observing the fusion of two galaxies called NGC7733 and NGC 7734 in our celestial quarter when they detected unusual emissions from the center of it and a curious movement of a large bright cluster inside it, which had a different speed than NGC7733. Inferring that it was an independent galaxy, scientists named it NGC7733N. There are supermassive black holes, which have a size of several million solar masses, in the centers of galaxies, and are known as galactic active nuclei. Because they “accumulate” matter, they often have a glow around them that can be observed by light spectroscopy.
The three merging black holes were part of the galaxies in the constellation Toucan. They are quite far away when you think of our nearest galactic neighbor: the Andromeda galaxy is 2.5 million light-years away. However, the document describes them as nearby galaxies. “In Astronomy everything is relative. When we study the solar system, we say that Mercury is closer and Jupiter is far … Compared to the nearest neighboring galaxy Andromeda, galaxies NGC7733, 7734 and 7733 N are quite far apart, but compared to size of the universe are nearby galaxies, ”says Jyoti Yadav, a doctoral student at the Indian Institute of Astrophysics and first author of the work published as a letter in the journal Astronomy and Astrophysics.
The study used data from the Ultraviolet Imaging Telescope (UVIT) aboard the first Indian space observatory ASTROSAT, the European full-field optical telescope called MUSE mounted on the Very Large Telescope (VLT) in Chile, and infrared optical telescope (IRSF) images. in South Africa.
In an email to Hinduism, Mousumi Das, of the Indian Institute of Astrophysics, an author of the work, says they were studying the active galactic nuclei of the two massive barred spiral galaxies NGC7733 and NGC7734 and that the detection of the third was surprising. “It was a bit like buying two and getting one for free,” says Dr. Das. “The project’s PI confirmed our suspicions using spectroscopic data from a European telescope called MUSE in Chile.”
The group observed these galaxies with an infrared telescope near South Africa. “Then, as they seemed interesting, we also observed them with UVIT [onboard ASTROSAT]”, Says Dr. Das. “We also found optical data in the MUSE archive. Therefore, we did not have to do optical spectroscopy.
Parsec final
In a statement from the Press Information Office, the team explains that if two galaxies collide, their black hole will also approach by transferring kinetic energy to the surrounding gas. The distance between the black holes decreases over time until the separation is around one parsec (3.26 light-years). The two black holes cannot lose any other kinetic energy to approach and fuse. This is known as the final parsec problem. The presence of a third black hole can solve this problem. “The two can get closer when another black hole or a star passes and it takes them a little out of their combined angular momentum,” Dr. Das explains. Therefore, the dual fusion black holes fuse with each other in the presence of a third.
Many pairs of active galactic nuclei (AGN, supermassive black hole in the center of a galaxy) have been detected in the past, but triple AGN is extremely rare and only a handful have been detected before using observations of X-rays. “Multiple accreting black holes [AGN] perhaps more common in our universe and especially common in galaxy clusters. Therefore, the growth of black holes can be driven by these group mergers, ”he says. This is only the third detection of this system.
“What is striking about this work is the use of several telescopes around the world (and one in space) to determine the presence of 3 AGNs. In fact, this use of multiple telescopes and observation bands is essential to conducting good astronomical research. This also shows how astrophysics is a truly collaborative science, ”says Preeti Kharb, who is part of the National Center for Radio Astrophysics – Tata Institute for Fundamental Research (NCRA-TIFR), Pune, which did not participate in this work.