quásares

Quasars are highly luminous active galactic nuclei powered by accretion onto supermassive black holes at the centers of distant galaxies. They emit across the electromagnetic spectrum and often appear point-like in optical images.

The term quasar, short for quasi-stellar object, arose from their star-like optical appearance and strong redshifted emission lines. The first identified quasar, 3C 273, was found in 1963 with z ≈ 0.158.

The engine is an accretion disk around a supermassive black hole. Gravitational energy heats the disk, producing vast radiation; a hot corona emits X-rays, and some quasars launch relativistic jets.

Quasars are extremely luminous, with bolometric luminosities up to 10^47 erg/s, and exhibit broad emission lines in the optical/ultraviolet region. They span redshifts from near-zero to beyond 7.

They are important cosmological probes, used to study the intergalactic medium, reionization, and the growth of large-scale structure. Absorption features in their spectra trace intervening gas along the line of sight.

Host galaxies are typically massive and can host intense star formation. Quasar activity is linked to gas inflows, mergers, and feedback processes that influence galaxy evolution.

Quasars are broadly classified as radio-loud or radio-quiet. Large surveys such as the Sloan Digital Sky Survey and 2dF have identified thousands of quasars, enabling statistical studies.