Astrophysics Group

Cavendish Laboratory

Galaxies and Quasars

Mullard Radio Astronomy Observatory
Galaxies and Quasars

spiralAll galaxies emit radio waves as well as light. Most are relatively weak sources, like this edge-on spiral galaxy mapped here by the Ryle telescope. Studies like this tell us about hot gas, star formation, cosmic rays and supernovae; we can also use radio spectral lines, especially from hydrogen, water vapour and carbon monoxide, to work out the internal dynamics of the galaxies.

A small fraction of galaxies have `active nuclei’, smaller than a millionth of the diameter of the galaxy but radiating more than all the rest of the galaxy in infra-red, light and X-rays. Often, they shoot out two jets, magnetic fields and very fast electrons (see below). These we see as quasars or radio galaxies as the jets collide with the tenuous intergalactic gas, somewhat like immense versions of the structures produced in regions of star formation.

The jets are believed to move at nearly the speed of light, so that their radiation is beamed forwards,. This explains why we often see one very bright jet – the one coming towards us. Quasars, the most powerful sources, often show a prominent jet, strong radio galaxies like the one to the right more usually don’t.AGN

The most powerful of these radio sources can be detected at immense distances in the Universe – the signals have taken thousands of millions of years to reach us.

For more information about our work, follow the links on the left.