Quasar

A quasar is an extremely luminous active galactic nucleus powered by matter falling toward a supermassive black hole. Its compact central engine can outshine the stars in its host galaxy.

Accretion disk: A rotating structure of gas and dust that spirals inward around a central object, releasing energy through friction and compression. In a quasar, the disk around the black hole supplies most of the observed luminosity.
3C 273: A bright quasar in the constellation Virgo, identified as the first quasar with a measured redshift. Its spectrum and distance established that at least some star-like radio sources lie far beyond the Milky Way.
Lyman-alpha forest: A series of absorption lines in distant objects’ spectra produced by intervening clouds of neutral hydrogen. Quasar light illuminates hydrogen clouds across vast stretches of the early universe.
Seyfert galaxy: A galaxy with a bright active nucleus whose surrounding host galaxy is visibly prominent. Seyfert nuclei share quasar-like activity but are generally less luminous.
Supermassive black hole: A black hole with a mass ranging from hundreds of thousands to billions of times the Sun’s mass. Its gravity anchors the compact engine at the center of a quasar.
Maarten Schmidt: A Dutch-American astronomer who recognized the redshifted emission lines in 3C 273’s spectrum in 1963. His identification revealed the extraordinary distance and luminosity of quasars.
Gravitational lens: A massive foreground object that bends light from a more distant source through gravity. Lensed quasars reveal intervening mass and can produce measurable time delays.
Blazar: An active galactic nucleus whose relativistic jet points close to the observer’s line of sight. Jet alignment makes blazars highly variable and strongly beamed compared with typical quasars.
Relativistic jet: A narrow outflow of particles moving close to the speed of light. Some quasars launch jets that carry energy far beyond their host galaxies.
Radio astronomy: The study of celestial objects through radio waves emitted or absorbed in space. Radio surveys first found many of the star-like sources later identified as quasars.

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