Quasars
A quasar is an extremely luminous active galactic nucleus powered by a supermassive black hole. The name comes from "quasi-stellar radio source" because when first discovered in the 1950s, they looked like faint stars but emitted radio waves. Gas falling into the black hole heats up and releases tremendous energy. The most powerful quasars have luminosities thousands of times greater than the Milky Way. Quasars matter because they are cosmic lighthouses that help us understand the early universe—they were more common billions of years ago and can be seen from vast distances, allowing astronomers to study the universe's history and structure.
Sources
- en.wikipedia.org: “A quasar ( KWAY-zar) is an extremely luminous active galactic nucleus (AGN).”
- en.wikipedia.org: “The emission from an AGN is powered by accretion onto a supermassive black hole with a mass ranging from millions to tens of billions of solar masses, surrounded by a gaseous accretion disc.”
- en.wikipedia.org: “The radiant energy of quasars is enormous; the most powerful quasars have luminosities thousands of times greater than that of a galaxy such as the Milky Way.”
- en.wikipedia.org: “The term quasar originated as a contraction of "quasi-stellar [star-like] radio source"—because they were first identified during the 1950s as sources of radio-wave emission of unknown physical origin—and when identified in photographic images at visible wavelengths, they resembled faint, star-like points of light.”
- en.wikipedia.org: “Quasar discovery surveys have shown that quasar activity was more common in the distant past; the peak epoch was approximately 10 billion years ago.”