Radio Stars (or Quasars)

The `radio stars' used to measure the twinkling effect are not stars at all, but are actually quasars, the brightest objects in the entire universe. Quasars are thought to be black holes at the centre of galaxies that feed on gas and stars to generate the massive amount of energy they give out.

When they were first discovered they looked very much like stars, and were found to emit a large amount of radio waves, hence they were given the name `quasi-stellar radio sources' or quasars for short. Afterwards it was found that quasars do not all emit large amounts of radio waves and so another name, quasi-stellar objects (or QSOs), has been suggested, but most people still call them quasars.

*** have a radio picture of a quasar here?