ISRO Missions and Discoveries

[pib] What are Blazars?


From UPSC perspective, the following things are important :

Prelims level : Blazars

Mains level : Black Holes, Blazars

Researchers from the Indian Institute of Astrophysics (IIA), Bangalore have conducted the first systematic study on the gamma-ray flux variability nature on different types of Blazars.

Strange terminologies from space-based studies are very important from prelims point of view.  We can expect a statement based question seeking to identify the term which is being referred to in the paragraph.

What are Blazars?

  • At the center of most galaxies, there’s a massive black hole that can have mass of millions or even billions of Suns that accrete 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).
  • A minority of AGN (~15%) emit collimated charged particles called jets travelling at speeds close to the speed of light.
  • Blazars are AGN whose jets are aligned with the observer’s line of sight.
  • Some blazars are thought to host binary black holes in them and could be potential targets for future gravitational-wave searches.

Studying blazars

  • Blazars are the most luminous and energetic objects in the known universe were found to be emitters of gamma-rays in the 1990s.
  • It is only with the capability of Fermi Gamma-ray space telescope (launched in 2008) to scan the entire sky once in three hours one is able to probe the flux variability characteristics of blazars on a range of time scales.
  • Gamma-ray band is one of the bands of the electromagnetic spectrum on which there is limited knowledge on the flux variability of blazars.
  • Major problem while studying them is to localize the site for the production of gamma-rays.


  • The study of blazars could provide clues to the processes happening close to the black hole, not visible through direct imaging.
  • Exploring blazars will provide key inputs to constrain the high energy production site as well as the high energy emission processes.

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