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.

Although they looked like stars they were also 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 not all quasars emit large amounts of radio waves and so another name, quasi-stellar object (or QSO), has been suggested, but most people still call them quasars.

Below is a different sort of "picture" of a radio star, one that I use in my work. It's not a photograph but a contour map of brightness. The contours represent the changing brightness - in the same way contours on an ordinary map show the changing ground height.

The radio star (called by its catalogue number of 1229+020) is the small, steeply contoured patch in the upper left of the diagram.