IAS Gyan

Daily News Analysis

Active Galactic Nuclei (AGN)

28th August, 2021 Science and Technology


  • Indian researchers have discovered three supermassive black holes from three galaxies merging together to form a triple active galactic nucleus, a compact region at the center of a newly discovered galaxy that has a much-higher-than-normal luminosity.


Super-Massive Black Hole & AGN

  • At the center of most galaxies, there’s a massive black hole.
  • The concentration of matter here is so dense that even light can’t escape from it.
  • They have mass of millions or even billions of Suns.
  • The black hole accretes gas, dust, and stellar debris around it.
  • As these material falls towards the black hole, their gravitational energy gets converted to light forming active galactic nuclei (AGN).
  • 15 % of AGN emit charged particles called jets travelling at speeds close to the speed of light.


  • An Active Galactic Nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum.
  • Such excess non-stellar (not from star) emission has been observed in the radio, microwave, infrared, optical, ultra-violet, X-ray and gamma ray wavebands.
  • A galaxy hosting an AGN is called an "active galaxy".
  • The observed characteristics of an AGN depend on several properties such as the mass of the central black hole, the rate of gas accretion onto the black hole, the orientation of the accretion disk, the degree of obscuration of the nucleus by dust, and presence or absence of jets.
  • Numerous subclasses of AGN have been defined based on their observed characteristics; the most powerful AGN are classified as quasars.
  • A blazar is an AGN with a jet pointed toward the Earth, in which radiation from the jet is enhanced by relativistic beaming.