quasar

A quasar (from quasi-stellar object or QSO) is an object with the point-like appearance of a star, but with a redshift indicating a far greater distance than that of a visible individual star. Quasars are identified now as active galactic nuclei. Observed redshifts range from .05 to greater than 7, putting them in the range of 600 million to near 13 billion light-years distant (or years old).

They appear bright enough that some quasars might equal the Sun's apparent brightness as seen from Earth at a distance of 30 light-years. However, they do not necessarily shine so brightly in all directions. Their strong light can be lensed by nearer objects and can be useful for studying the objects doing the lensing.

Quasars were first identified in the 1960s.

The Balmer series, typically H-alpha, is often useful to determine the redshift.

The term quasi-stellar source (or QSS or quasi-stellar radio source, also sometimes using the prefix QSR) refers to a quasar that is also a strong radio source In fact, the term quasar was originally coined for such radio sources, but is often used with the broader meaning. The term quasi-stellar galaxy (QSG) formerly was used for radio-quiet quasars. (Note that in radio astronomy, the word source is typically assumed to mean radio source).