Quasar

quasarsquasi-stellar objectQSOquasi-stellar objectsbrightest objects in the universeiron quasarradio-loud quasarsradioquasarsvariable quasars
A quasar (also known as a QSO or quasi-stellar object) is an extremely luminous active galactic nucleus (AGN).wikipedia
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Supermassive black hole

supermassive black holesblack holesuper massive black hole
It has been theorized that most large galaxies contain a supermassive central black hole with mass ranging from millions to billions of times the mass of our Sun.
Accretion of interstellar gas onto supermassive black holes is the process responsible for powering quasars and other types of active galactic nuclei.

ULAS J1342+0928

As of 2017, the most distant known quasar is ULAS J1342+0928 at redshift z = 7.54; light observed from this quasar was emitted when the Universe was only 690 million years old.
ULAS J1342+0928 is the most distant known quasar detected and contains the most distant and oldest known supermassive black hole, at a reported redshift of z = 7.54, surpassing the redshift of 7 for the previously known most distant quasar ULAS J1120+0641.

Radio astronomy

radio astronomerradioradioastronomy
But when radio astronomy commenced in the 1950s, astronomers detected, among the galaxies, a small number of anomalous objects with properties that defied explanation.
These include stars and galaxies, as well as entirely new classes of objects, such as radio galaxies, quasars, pulsars, and masers.

3C 273

3C2733C 273 quasar
The first quasars (3C 48 and 3C 273) were discovered in the late 1950s, as radio sources in all-sky radio surveys. Another radio source, 3C 273, was predicted to undergo five occultations by the Moon.
3C 273 is a quasar located in the constellation Virgo.

3C 48

3C48
The first quasars (3C 48 and 3C 273) were discovered in the late 1950s, as radio sources in all-sky radio surveys. In 1963, a definite identification of the radio source 3C 48 with an optical object was published by Allan Sandage and Thomas A. Matthews.
3C48 is a quasar discovered in 1960; it was the second source conclusively identified as such.

Thomas A. Matthews

Thomas Matthews
In 1963, a definite identification of the radio source 3C 48 with an optical object was published by Allan Sandage and Thomas A. Matthews.
He is credited with being one of the discoverers of the first quasar, 3C 48, in 1960 using a new interferometer at the Owens Valley Radio Observatory, along with Allan Sandage.

Maarten Schmidt

Schmidt, Maarten
Measurements taken by Cyril Hazard and John Bolton during one of the occultations using the Parkes Radio Telescope allowed Maarten Schmidt to find a visible counterpart to the radio source and obtain an optical spectrum using the 200-inch Hale Telescope on Mount Palomar.
Maarten Schmidt (born December 28, 1929) is a Dutch astronomer who measured the distances of quasars.

Astrophysical jet

relativistic jetjetsjet
As with other categories of AGN, the observed properties of a quasar depend on many factors including the mass of the black hole, the rate of gas accretion, the orientation of the accretion disk relative to the observer, the presence or absence of a jet, and the degree of obscuration by gas and dust within the host galaxy.
Most of the largest and most active jets are created by supermassive black holes (SMBH) in the centre of active galaxies such as quasars and radio galaxies or within galaxy clusters.

Occultation

occultedoccultsocculting
Another radio source, 3C 273, was predicted to undergo five occultations by the Moon.
This was crucial for the unambiguous identification of the radio source 3C 273 with the optical quasar and its jet, and a fundamental prerequisite for Maarten Schmidt's discovery of the cosmological nature of quasars.

Hong-Yee Chiu

astrophysicist Hong-Yee Chiu in May 1964, in Physics Today, to describe certain astronomically-puzzling objects:
He was also the first scientist to officially use the term "quasar," in 1964.

Energy

energiesenergy transfertotal energy
As gas falls toward the black hole, energy is released in the form of electromagnetic radiation, which can be observed across the electromagnetic spectrum.
In cosmology and astronomy the phenomena of stars, nova, supernova, quasars and gamma-ray bursts are the universe's highest-output energy transformations of matter.

Galaxy

galaxiesgalacticgalactic nuclei
It has been theorized that most large galaxies contain a supermassive central black hole with mass ranging from millions to billions of times the mass of our Sun.
* Seyfert galaxies or quasars, are classified depending on the luminosity, are active galaxies that emit high-energy radiation in the form of x-rays.

Hubble's law

Hubble constantcosmological redshiftHubble parameter
Schmidt noted that redshift is also associated with the expansion of the universe, as codified in Hubble's law.

Black hole

black holesblack-holeblackhole
Eventually, starting from about the 1970s, many lines of evidence (including the first X-Ray space observatories, knowledge of black holes and modern models of cosmology) gradually demonstrated that the quasar redshifts are genuine, and due to the expansion of space, that quasars are in fact as powerful and as distant as Schmidt and some other astronomers had suggested, and that their energy source is matter from an accretion disc falling onto a supermassive black hole.
Matter that falls onto a black hole can form an external accretion disk heated by friction, forming some of the brightest objects in the universe.

Galaxy merger

mergermergersmerging
High-resolution images of quasars, particularly from the Hubble Space Telescope, have demonstrated that quasars occur in the centers of galaxies, and that some host-galaxies are strongly interacting or merging galaxies.
This is thought to be the driving force behind many quasars.

Accretion disk

accretion discaccretion disksaccretion
Eventually, starting from about the 1970s, many lines of evidence (including the first X-Ray space observatories, knowledge of black holes and modern models of cosmology) gradually demonstrated that the quasar redshifts are genuine, and due to the expansion of space, that quasars are in fact as powerful and as distant as Schmidt and some other astronomers had suggested, and that their energy source is matter from an accretion disc falling onto a supermassive black hole. In quasars and other types of AGN, the black hole is surrounded by a gaseous accretion disk.
The most spectacular accretion disks found in nature are those of active galactic nuclei and of quasars, which are thought to be massive black holes at the center of galaxies.

Radio galaxy

radio galaxiesradio lobeFR I radio galaxy
In the 1980s, unified models were developed in which quasars were classified as a particular kind of active galaxy, and a consensus emerged that in many cases it is simply the viewing angle that distinguishes them from other active galaxies, such as blazars and radio galaxies.
Radio galaxies and their relatives, radio-loud quasars and blazars, are types of active galaxy nuclei that are very luminous at radio wavelengths, with luminosities up to 10 39 W between 10 MHz and 100 GHz.

John Gatenby Bolton

John Bolton
British-Australian astronomer John Bolton made many early observations of quasars, including a breakthrough in 1962.
This telescope found some distant radio sources now known to be quasars.

ULAS J1120+0641

The highest redshift quasar known is ULAS J1120+0641, with a redshift of 7.085, which corresponds to a comoving distance of approximately 29 billion light-years from Earth (these distances are much larger than the distance light could travel in the universe's 13.8 billion year history because [[Metric expansion of space#How are distances between two points measured if space is expanding?|space itself has also been expanding]]).
ULAS J1120+0641 is the second most distant known quasar as of 6 December 2017, after ULAS J1342+0928.

General relativity

general theory of relativityrelativitygeneral relativity theory
A common alternative explanation was that the redshifts were caused by extreme mass (gravitational redshifting explained by general relativity) and not by extreme velocity (explained by special relativity).
Physicists began to understand the concept of a black hole, and to identify quasars as one of these objects' astrophysical manifestations.

Gravitational lens

gravitational lensinggravitationally lenseddeflection of light
This included crucial evidence from optical and X-Ray viewing of quasar host galaxies, finding of 'intervening' absorption lines which explained various spectral anomalies, observations from gravitational lensing, Peterson and Gunn's 1971 finding that galaxies containing quasars showed the same redshift as the quasars, and Kristian's 1973 finding that the "fuzzy" surrounding of many quasars was consistent with a less luminous host galaxy.
The lensing object may be stars in the Milky Way in one typical case, with the background source being stars in a remote galaxy, or, in another case, an even more distant quasar.

APM 08279+5255

The hyperluminous quasar APM 08279+5255 was, when discovered in 1998, given an absolute magnitude of −32.2.
APM 08279+5255 is a very distant, broad absorption line quasar located in the constellation Lynx.

Special relativity

special theory of relativityrelativisticspecial
A common alternative explanation was that the redshifts were caused by extreme mass (gravitational redshifting explained by general relativity) and not by extreme velocity (explained by special relativity).
Another example where visual appearance is at odds with measurement comes from the observation of apparent superluminal motion in various radio galaxies, BL Lac objects, quasars, and other astronomical objects that eject relativistic-speed jets of matter at narrow angles with respect to the viewer.

Lovell Telescope

Mark Ifirst of theseLovell
Using small telescopes and the Lovell Telescope as an interferometer, they were shown to have a very small angular size.
The early investigation into the size and nature of quasars drove the development of interferometry techniques in the 1950s; the Lovell telescope had an advantage due to its large collecting area, meaning that high sensitivity interferometer measurements can be made relatively quickly using it. As a result, the telescope featured heavily in the discovery of quasars.

Seyfert galaxy

Seyfert galaxiesSeyfertSeyfert 2
Since quasars exhibit all the properties common to other active galaxies such as Seyfert galaxies, the emission from quasars can be readily compared to those of smaller active galaxies powered by smaller supermassive black holes.
Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars.