Rare merging of three supermassive black holes


  • A rare merging of three supermassive black holes has been spotted by a team of astrophysicists in India.

Key Findings on three supermassive black holes

  • The study used data from the Ultraviolet 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.

    three supermassive black holes
    Source: REUTERS
  • They were observing the merging of two galaxies named NGC7733 and NGC 7734 in our celestial neighbourhood when they detected unusual emissions from the centre of the latter and a curious movement of a large bright clump within it, having a different velocity than that of NGC7733.
  • Inferring that this was a separate galaxy, the scientists named it NGC7733N.
  • There are supermassive blackholes, which are several million solar masses in size, at the centres of galaxies, and these are known as Active Galactic Nuclei.
  • Since they “accrete“ matter, they often have a glow around them which can be observed using light spectroscopy.
  • All three merging black holes were part of galaxies in the Toucan constellation.
    • It is located in the southern hemisphere of the sky. It is visible at latitudes south of 15 degrees between August and October. It is completely below the horizon for anyone north of 30 degrees. It is a small constellation, occupying an area of 295 square degrees.

Parsec Problem

  • The team explains that if two galaxies collide, their black hole will also come closer by transferring the kinetic energy to the surrounding gas.
  • The distance between the blackholes decreases with time until the separation is around a parsec (3.26 light-years).
  • The two black holes are then unable to lose any further kinetic energy 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.
  • Many Active Galactic Nuclei (AGN, supermassive black hole at the centre of a galaxy) pairs have been detected in the past, but triple AGN are extremely rare, and only a handful has been detected before using X-ray observations. “Multiple accreting black holes [AGN] maybe more common in our universe and especially common in galaxy groups. So the growth of black holes may be driven by such mergers in groups.

Source : The Hindu

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