What are Quasars?
Quasars (or quasi-stella objects) are extremely luminous objects at immense distances. This is hinted at by the name quasar; they appear star-like but outshine whole galaxies. The remarkable thing is the apparently small size of these objects.

Discovery of Quasars
The story of the discovery of quasars begins around 1960, when Allan Sandage used the Mount Palomar Telescope to look for a star at the location of a strong radio source. The star's spectrum exhibited a series of bright lines that nobody could identify. Within a couple of years, several more similar 'stars' were discovered, each associated with a strong source of radio waves.
    These new objects were at first thought to be an usual type of galaxy. However, these new radio sources turned out to be very compact, and their energy output exceeded that which could beaccounted for by the stars they appeared to contain. Optical observations confirmed the objects as star-like, rather than fuzzy, as they would appear to be if they were galaxies.
    Since quasars have continuous spectra with emission lines crossing them, they were initially thought to be simply a type of star. But the emission lines did not match up with any known elements.
The puzzle was solved in 1963, when astronomer Maarten Schmidt compared the spectrum of quasar 3C273 with the Balmer series of hydrogen spectrum. It was found that the two matched up when the spectra was shifted along relative to one another.
    The hydrogen lines had been shifted by 15.8% towards the red end of the spectrum. This means that the frequency of the light had decreased and the 'star' was moving awat from us. In fact, 3C273 was moving away at a speed of 45 000 km/s (15% the speed of light).
    So the first quasars were found by matching up radio sources with star-like objects that exhibited strong red-shifts. because large radio telescopes have high angular resolution, it was possible to say that these objects are smaller than galaxies. Of the quasars now known, only about 3% are radio sources.

Quasars and the black hole
Quasars have red shifts which suggest that they are the most distant objects in the Universe. If they are really distant, they would radiate as much energy as some galaxies, but have only the volume of the solar system. Each may be the active centre of a galaxy where nebular matter surrounds a supermassive black hole.In fact, the super-massive black hole is believed by many theoreticians to be responsible for the radiation from quasars. Quasars illustrates the importance of gravity as an energy reservoir. Quasars; unlike most stars, which rely mostly on their nuclear reactors to supply their luminosities, have very compact, powerful, efficient energy machines. And black holes of the supermassive kind appear to fit the bill as one.