In 1963, which quasar became the first to be identified?

3C 273 became the first identified quasar in 1963. Its name comes from the Third Cambridge Catalogue of radio sources, where it was listed as the 273rd entry.

Astronomers had detected unusual radio sources that looked star-like in visible-light images. Because they appeared point-like but produced powerful radio emissions, they were called “quasi-stellar radio sources,” shortened to quasars. Optical astronomer Maarten Schmidt identified the strange spectral lines of 3C 273 as hydrogen shifted by a large redshift.

That redshift showed that 3C 273 was extremely distant, yet far brighter than a normal star. Its energy comes from matter falling toward a supermassive black hole at the centre of its host galaxy. Quasars are therefore active galactic nuclei, not stars, despite their starlike appearance.

3C 273 is also notable for having a visible jet and remaining bright enough for amateur telescopes under suitable conditions. The later discovery of many more quasars helped establish that black-hole-powered activity can illuminate the distant universe.