Definition and Characteristics

A quasar, or quasi-stellar object (QSO), is an exceptionally luminous active galactic nucleus (AGN) powered by a supermassive black hole. These objects emit energy across the entire electromagnetic spectrum, including radio, optical, ultraviolet, and X-ray wavelengths, often outshining their host galaxies. The term "quasar" originates from "quasi-stellar radio source," reflecting their initial identification as star-like radio sources in the 1950s. Source

Discovery and Observation

Quasars were first identified in the 1960s when astronomers detected strong radio emissions from point-like sources. Subsequent optical observations revealed that these sources exhibited high redshifts, indicating they were extremely distant and luminous. The first quasar to be identified was 3C 273, located in the constellation Virgo, which remains one of the brightest and closest quasars known. Source

Structure and Energy Source

At the core of a quasar lies a supermassive black hole surrounded by an accretion disk of infalling material. As matter spirals into the black hole, it heats up due to gravitational and frictional forces, emitting vast amounts of energy. This process results in the quasar's extraordinary luminosity, which can be up to a thousand times greater than that of the Milky Way galaxy. Source

Distribution and Distance

Quasars are among the most distant objects observable in the universe, with some located over 13 billion light-years away. Their high redshifts indicate that they existed in the early universe, providing valuable insights into cosmic evolution. The most distant known quasar, J0313–1806, is observed as it was when the universe was only 670 million years old. Source

Role in Galaxy Evolution

Quasars play a significant role in the formation and evolution of galaxies. The intense radiation and outflows from quasars can influence star formation in their host galaxies, either triggering or suppressing it. This feedback mechanism affects the growth and development of galaxies over cosmic time. Source

Notable Quasars

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  3C 273: The first quasar identified, located in the constellation Virgo, and one of the brightest known.

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  J0313–1806: The most distant known quasar, observed as it was when the universe was only 670 million years old. Source

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  J0529-4351: Identified as the most luminous object in the universe, with a supermassive black hole consuming the equivalent of a sun each day. Source

Observational Techniques

Studying quasars involves multi-wavelength observations using various telescopes and instruments. Optical and radio telescopes detect their emissions, while X-ray and infrared observations provide insights into the high-energy processes occurring near the black hole. Instruments like the Hubble Space Telescope have been instrumental in resolving details of quasars and their host galaxies. Source

Significance in Cosmology

Quasars serve as important tools in cosmology, acting as beacons to study the intergalactic medium and the large-scale structure of the universe. Their high luminosity allows astronomers to probe the conditions of the early universe and understand the processes governing galaxy formation and evolution. Source

Future Research

Ongoing and future observational campaigns aim to uncover more about these enigmatic objects. The James Webb Space Telescope (JWST) is expected to provide deeper insights into the nature of quasars, their formation, and their role in the early universe. Source