Active galactic nucleus

Active galactic nucleus


  • Recently, Scientists said that their observations involving the supermassive black hole at the centre of galaxy Messier 77 and its surrounding cloud lend support to predictions made three decades ago about what are called active galactic nuclei.

Key Findings

  • Observations showing a roughly dough-nut-shaped cloud of cosmic dust and gas shrouding a huge black hole at the heart of a galaxy similar in size to our Milky Way are providing scientists with new clarity about the universe’s most energetic objects.
  • Active galactic nuclei are places at the centres of many large galaxies that have tremendous luminosity – sometimes outshining all of a galaxy’s billions of stars combined – and produce the universe’s most energetic outbursts seen since the Big Bang event 13.8 billion years ago.

    Active galactic nucleus
    Photo Credit: Getty Images
  • The energy arises from gas violently falling into a supermassive black hole that is surrounded by a cloud of tiny particles of rock and soot along with mostly hydrogen gas.
  • Black holes are extraordinarily dense objects possessing gravitational pulls so powerful even light cannot escape them.
  • Supermassive black holes, which reside at the centre of many galaxies, including our own, are the largest of them.

About Messier 77

  • Messier 77, also called NGC 1068 or the Squid Galaxy, is located 47 million light years – the distance light travels in a year, 9.5 trillion km – from the Earth in the constellation Cetus. Its supermassive black hole has a mass roughly 10 million times greater than our sun.
  • Messier 77’s active galactic nucleus is one of the dark ones, but the new observations indicate that it actually possesses the same qualities as the bright ones.

Back to Basics

About Active galactic nucleus

  • 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 with characteristics indicating that the luminosity is not produced by stars.
  • Such excess non-stellar 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 non-stellar radiation from an AGN is theorized to result from the accretion of matter by a supermassive black hole at the center of its host galaxy.
  • Active galactic nuclei are the most luminous persistent sources of electromagnetic radiation in the universe, and as such can be used as a means of discovering distant objects; their evolution as a function of cosmic time also puts constraints on models of the cosmos.


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