Indian researchers discover cosmic collision

Context

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.

Discovered triple merging galaxy

• The rare occurrence of 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.
• The emission line analysis from the central regions of NGC 7733 and NGC 7734 shows Seyfert and low ionization nuclear emission-line regions type AGN activity.
• The galaxy pair NGC 7733−34 also shows evidence of a third component, which has Seyfert-like emission.
• The galaxy pair NGC 7733−34 forms a triple-AGN system. We also detected an extended narrow-line region associated with the nucleus of NGC 7733.
• 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.
• Researchers 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.
• Infrared images from the optical telescope (IRSF) traced by the South African Astronomical Observatory (SAAO) 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.

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.
• 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.