Lecture 26 - Radio Galaxies

Radio emission detected for the first time from an external galaxy Cygnus A and the suggestion that it could be a 'double radio source' compelled the radio astronomers to find ways of attaining very high angular resolution of celestial radio sources. This led to the discovery of the "Aperture Synthesis" telescope by Sir Martin Ryle, for which he was awarded the Nobel Prize in 1974 (first Nobel in Astronomy, along with Anthony Hewish).

The Giant Meterwave Radio Telescope (near Pune) is largest among such telescopes in the low frequency regime. Nowadays GMRT is routinesly used for observing Radio Galaxies, sometimes revealing interesting morphologies where the energetic jets emitted by these galaxies twist, wrap, overlap and bend.

Radio emission from an external galaxy was first detected around 1950 from the powerful galaxy Cygnus A. There was a suggestion that it was a `double radio source'. This discovery catalyzed the quest for achieving higher angular resolution. This led to the discovery of "Aperture Synthesis" telescopes. Sir Martin Ryle in Cambridge was awarded the Nobel Prize for this discovery. Observations with high angular resolution revealed a remarkable morphology of `Radio Galaxies'. There was a compact central source, presumed to be a super-massive black hole. There were two relativistic jets of particles emanating from the central source, and two gigantic 'lobes' of radio emission at both ends of the jet. This lecture is intended to be an introduction to the world of giant radio galaxies.