An artist's impression of a growing quasar.

A Quasar (contraction of QUASi-stellAR radio source) is an extremely powerful and distant active galactic nucleus. An active galactic nucleus ( AGN) is a compact region at the centre of a Galaxy which has a much higher than normal luminosity over some or all of the Electromagnetic They were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light that were point-like, similar to stars, rather than extended sources similar to galaxies. In Physics and Astronomy, redshift occurs when Electromagnetic radiation – usually Visible light – emitted or reflected by Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. Radio frequency ( RF) is a Frequency or rate of Oscillation within the range of about 3 Hz to 300 GHz A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth While there was initially some controversy over the nature of these objects, there is now a scientific consensus that a quasar is a compact region 10-10000 Schwarzschild radii across surrounding the central supermassive black hole of a galaxy. Scientific consensus is the collective judgement position and Opinion of the community of Scientists in a particular field of Science at a particular The Schwarzschild radius (sometimes historically referred to as the gravitational radius) is a characteristic Radius associated with every Mass. A supermassive black hole is a Black hole with a Mass of an order of magnitude between 105 and 1

Overview

Quasars show a very high redshift which is an effect of the expansion of the universe between the quasar and the Earth. In Physics and Astronomy, redshift occurs when Electromagnetic radiation – usually Visible light – emitted or reflected by The metric expansion of space is the averaged increase of metric (i When combined with Hubble's law, the implication of the redshift is that the quasars are very distant. Hubble's law is the statement in Physical cosmology that the Redshift in light coming from distant galaxies is proportional to their distance To be observable at that distance, the energy output of quasars dwarf every other astronomical event. The most luminous quasars radiate at a rate that can exceed the output of average galaxies, equivalent to one trillion (10¹²) suns. A galaxy is a massive gravitationally bound system consisting of Stars an Interstellar medium of gas and dust, and Dark matter This radiation is emitted across the spectrum, almost equally, from X-rays to the far-infrared with a peak in the Ultraviolet-optical bands, with some quasars also being strong sources of radio and of gamma-rays. In early optical images, quasars looked like single points of light (i. e. point source), indistinguishable from stars, except for their peculiar spectra. A point source is a single identifiable localized source of something With infrared telescopes and the Hubble Space Telescope, the "host galaxies" surrounding the quasars have been identified in some cases. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into ^[1] These galaxies are normally too dim to be seen against the glare of the quasar, except with these special techniques. Most quasars cannot be seen with small telescopes, but 3C 273, with an average apparent magnitude of 12. 3C 273 is a Quasar located in the Constellation Virgo. It is the Optically brightest quasar in our sky ( m ~ 12 The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value 9, is an exception. At a distance of 2. 44 billion light-years (lt-yr), it is one of the most distant objects directly observable with amateur equipment. A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by

Some quasars display rapid changes in luminosity in the optical and even more rapid in the X-rays, which implies that they are small (Solar System sized or less) as an object cannot change faster than the time it takes light to travel from one end to the other; but relativistic beaming of jets pointed nearly directly toward us explains the most extreme cases). Luminosity has different meanings in several different fields of science Relativistic beaming is the process by which the relativistic effect modifies the apparent luminosity of a Relativistic jet. The highest redshift known for a quasar (as of December 2007) is 6. In Physics and Astronomy, redshift occurs when Electromagnetic radiation – usually Visible light – emitted or reflected by December 2007 is the twelfth month of that year It began on a Saturday and 31 days later ended on a Monday 43,^[2] which corresponds (assuming the currently-accepted value of 71 for the Hubble Constant) to a distance of approximately 28 billion light-years. Hubble's law is the statement in Physical cosmology that the Redshift in light coming from distant galaxies is proportional to their distance A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by (NB there are some subtleties in distance definitions in cosmology, so that distances greater than 13. Distance measures are used in Physical cosmology to give a natural notion of the Distance between two objects or events in the Universe. 7 billion lt-yr, or even greater than 27. 4 = 2*13. 7 lt-yr, can occur. )

Quasars are believed to be powered by accretion of material into supermassive black holes in the nuclei of distant galaxies, making these luminous versions of the general class of objects known as active galaxies. In Astrophysics, the term accretion is used for at least two distinct processes A supermassive black hole is a Black hole with a Mass of an order of magnitude between 105 and 1 An active galactic nucleus ( AGN) is a compact region at the centre of a Galaxy which has a much higher than normal luminosity over some or all of the Electromagnetic Large central masses (10**6-10**9 Solar masses) have been measured in quasars using 'reverberation mapping'. Several dozen nearby large galaxies, with no sign of a quasar nucleus, have been shown to contain a similar central black hole in their nuclei, so it is thought that all large galaxies have one, but only a small fraction emit powerful radiation and so are seen as quasars. The matter accreting onto the black hole is unlikely to fall directly in, but will have some angular momentum around the black hole that will cause the matter to collect in an accretion disc

Knowledge of quasars is advancing rapidly. An accretion disc (or accretion disk) is a structure (often a Circumstellar disk) formed by diffuse material in orbital motion around a central body As recently as the 1980s, there was no clear consensus as to their origin.

Properties of quasars

More than 100,000 quasars are known, most from the Sloan Digital Sky Survey. The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic Redshift survey using a dedicated 2 All observed quasar spectra have redshifts between 0. In Physics and Astronomy, redshift occurs when Electromagnetic radiation – usually Visible light – emitted or reflected by 06 and 6. 4. Applying Hubble's law to these redshifts, it can be shown that they are between 780 million and 28 billion light-years away. Hubble's law is the statement in Physical cosmology that the Redshift in light coming from distant galaxies is proportional to their distance A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by Because of the great distances to the furthest quasars and the finite velocity of light, we see them and their surrounding space as they existed in the very early universe.

Most quasars are known to be farther than three billion light-years away. Although quasars appear faint when viewed from Earth, the fact that they are visible from so far away means that quasars are the most luminous objects in the known universe. The quasar that appears brightest in the sky is 3C 273 in the constellation of Virgo. 3C 273 is a Quasar located in the Constellation Virgo. It is the Optically brightest quasar in our sky ( m ~ 12 In common usage a constellation is a group of celestial bodies that are connected together in some arrangement typically stars to form a visible figure or picture Virgo ( Virgin, symbol, Unicode ♍ is a Constellation of the Zodiac. It has an average apparent magnitude of 12. The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value 8 (bright enough to be seen through a small telescope), but it has an absolute magnitude of −26. A telescope is an instrument designed for the observation of remote objects and the collection of Electromagnetic radiation. In Astronomy, absolute magnitude (also known as absolute visual magnitude) is the Apparent magnitude an object would have if it were at a standard 7. From a distance of about 33 light-years, this object would shine in the sky about as brightly as our sun. A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by The Sun (Sol is the Star at the center of the Solar System. This quasar's luminosity is, therefore, about 2 trillion (2 × 10¹²) times that of our sun, or about 100 times that of the total light of average giant galaxies like our Milky Way. Luminosity has different meanings in several different fields of science The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply

The hyperluminous quasar APM 08279+5255 was, when discovered in 1998, given an absolute magnitude of −32. In Astronomy, absolute magnitude (also known as absolute visual magnitude) is the Apparent magnitude an object would have if it were at a standard 2, although high resolution imaging with the Hubble Space Telescope and the 10 m Keck Telescope revealed that this system is gravitationally lensed. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into The W M Keck Observatory is a two-telescope Astronomical observatory at the 4145 meter (13600 ft summit of Mauna Kea in Hawai'i. A gravitational lens is formed when the light from a very distant bright source (such as a Quasar) is "bent" around a massive object (such as a cluster of A study of the gravitational lensing in this system suggests that it has been magnified by a factor of ~10. It is still substantially more luminous than nearby quasars such as 3C 273.

Quasars were much more common in the early universe. This discovery by Maarten Schmidt in 1967 was early strong evidence against the Steady State cosmology of Fred Hoyle, and in favor of the Big Bang cosmology. Maarten Schmidt (born December 28 1929) is a Dutch Astronomer who measured the distances of astronomical objects called Quasars Sir Fred Hoyle FRS ( 24 June, 1915  &ndash 20 August, 2001) was an English Astronomer primarily The Big Bang is the cosmological model of the Universe that is best supported by all lines of scientific evidence and Observation. Quasars show where massive black holes are growing rapidly (via accretion. These black holes grow in step with the mass of stars in their host galaxy in a way not understood at present. One idea is that the jets, radiation and winds from quasars shut down the formation of new stars in the host galaxy, a process called 'feedback'. The jets that produce strong radio emission in some quasars at the centers of clusters of galaxies are known to have enough power to prevent the hot gas in these clusters from cooling and falling down onto the central galaxy. Galaxy groups and clusters are the largest Gravitationally bound objects to have arisen thus far in the process of cosmic structure formation

Quasars are found to vary in luminosity on a variety of time scales. Some vary in brightness every few months, weeks, days, or hours. This means that quasars generate and emit their energy from a very small region, since each part of the quasar would have to be in contact with other parts on such a time scale to coordinate the luminosity variations. As such, a quasar varying on the time scale of a few weeks cannot be larger than a few light-weeks across. The emission of large amounts of power from a small region requires a power source far more efficient that the nuclear fusion which powers stars. The release of gravitational energy by matter falling towards a massive black hole is the only process known that can produce such high power continuously. (Stellar explosions - Supernovas and gamma-ray bursts - can do so, but only for a few minutes. A supernova (plural supernovae or supernovas) is a stellar Explosion. Gamma-ray bursts ( GRB s are the most luminous electromagnetic events occurring in the Universe since the Big Bang. ) Black holes were considered too exotic by some astronomers in the 1960s, and they suggested that the redshifts arose from some other (unknown) process, so that the quasars were not really so distant as the Hubble law implied. This 'redshift controversy' lasted for many years. Many lines of evidence (seeing host galaxies, finding 'intervening' absorption lines, gravitational lensing) now demonstrate that the quasar redshifts are due to the Hubble expansion, and quasars are as powerful as first thought.

Quasars have all the same properties as active galaxies, but are more powerful: Radiation is 'nonthermal' (i. Radiation, as in Physics, is Energy in the form of waves or moving Subatomic particles emitted by an atom or other body as it changes from a higher energy e. not due to a black body), and some are observed to have jets and lobes like those of radio galaxies. In Physics, a black body is an object that absorbs all light that falls on it Radio galaxies and their relatives radio-loud Quasars and Blazars, are types of Active galaxy that are very luminous at radio wavelengths (up Quasars can be detected over the entire observable electromagnetic spectrum including radio, infrared, optical, ultraviolet, X-ray and even gamma rays. The electromagnetic (EM spectrum is the range of all possible Electromagnetic radiation frequencies Radio waves are electromagnetic waves occurring on the Radio frequency portion of the Electromagnetic spectrum. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays X-radiation (composed of X-rays) is a form of Electromagnetic radiation. Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions Most quasars are brightest in their rest-frame near-ultraviolet (near the 1216 angstrom (121. An ångström or angstrom (symbol Å) (ˈɔːŋstrəm Swedish: ˈɔ̀ŋstrœm is an internationally recognized non- SI unit of length equal 6 nm) Lyman-alpha emission line of hydrogen), but due to the tremendous redshifts of these sources, that peak luminosity has been observed as far to the red as 9000 angstroms (900 nm or 0. A nanometre ( American spelling: nanometer, symbol nm) ( Greek: νάνος nanos dwarf; μετρώ metrό count) is a In Physics, the Lyman series is the series of transitions and resulting Emission lines of the Hydrogen Atom as an Electron goes from 9 µm), in the near infrared. A minority of quasars show strong radio emission, which originates from jets of mater moving close to the speed of light. When looked at down the jet, these appear as a blazar and often have regions that appear to move away from the center faster than the speed of light (superluminal expansion). A blazar is a very compact and highly variable energy source associated with a presumed Supermassive black hole at the center of a Host galaxy. This is an optical trick due to the properties of special relativity. Special relativity (SR (also known as the special theory of relativity or STR) is the Physical theory of Measurement in Inertial

Quasar redshifts are measured from the strong spectral lines that dominate their optical and ultraviolet spectra. In Physics and Astronomy, redshift occurs when Electromagnetic radiation – usually Visible light – emitted or reflected by A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range compared These lines are brighter than the continuous spectrum, so they are called 'emission' lines. They have width of several percent of the speed of light which are due to Doppler shifts due to the high speeds of the gas emitting the lines. Fast motions strongly indicate a large mass. Emission lines of hydrogen (mainly of the Lyman series and Balmer series), Helium, Carbon, Magnesium, Iron and Oxygen are the brightest lines. In Physics, the Lyman series is the series of transitions and resulting Emission lines of the Hydrogen Atom as an Electron goes from The Balmer series or Balmer lines in Atomic physics, is the designation of one of a set of six different named series describing the Spectral line emissions The atoms emitting these lines range from neutral to highly ionized. (I. e. many of the electrons are stripped of the ion, leaving it highly charged. ) This wide range of ionization shows that the gas is highly irradiated by the quasar, not is not merely hot, and not by stars, which cannot produce such a wide range of ionization

Iron Quasars show strong emission lines resulting from ionized iron, such as IRAS 18508-7815. Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26

Quasar emission generation

This view, taken with infrared light, is a false-color image of a quasar-starburst tandem with the most luminous starburst ever seen in such a combination.

Since quasars exhibit properties common to all active galaxies, the emissions from quasars can be readily compared to those of small active galaxies powered by supermassive black holes. An active galactic nucleus ( AGN) is a compact region at the centre of a Galaxy which has a much higher than normal luminosity over some or all of the Electromagnetic A supermassive black hole is a Black hole with a Mass of an order of magnitude between 105 and 1 To create a luminosity of 10⁴⁰ W (the typical brightness of a quasar), a super-massive black hole would have to consume the material equivalent of 10 stars per year. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. The brightest known quasars devour 1000 solar masses of material every year. The largest known is estimated to consume matter equivalent to 600 Earths per hour. Quasars 'turn on' and off depending on their surroundings, and since quasars cannot continue to feed at high rates for 10 billion years, after a quasar finishes accreting the surrounding gas and dust, it becomes an ordinary galaxy.

Quasars also provide some clues as to the end of the Big Bang's reionization. The Big Bang is the cosmological model of the Universe that is best supported by all lines of scientific evidence and Observation. In Big Bang cosmology, reionization is the process that reionized the matter in the Universe after the " dark ages. The oldest quasars (redshift > 4) display a Gunn-Peterson trough and have absorption regions in front of them indicating that the intergalactic medium at that time was neutral gas. In Physics and Astronomy, redshift occurs when Electromagnetic radiation – usually Visible light – emitted or reflected by In Astronomical spectroscopy, the Gunn-Peterson trough is a feature of the spectra of Quasars due to the presence of neutral hydrogen in the Intergalactic Intergalactic space is the physical space between galaxies. Generally free of dust and debris intergalactic space is very close to a total Vacuum. More recent quasars show no absorption region but rather their spectra contain a spiky area known as the Lyman-alpha forest. In Astronomical spectroscopy, the Lyman alpha forest is the sum of Absorption lines arising from the Lyman alpha transition of the neutral Hydrogen This indicates that the intergalactic medium has undergone reionization into plasma, and that neutral gas exists only in small clouds.

One other interesting characteristic of quasars is that they show evidence of elements heavier than helium, indicating that galaxies underwent a massive phase of star formation, creating population III stars between the time of the Big Bang and the first observed quasars. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Star Formation is the process by which dense parts of Molecular clouds collapse into a ball of plasma to form a Star. In Astronomy and Physical cosmology, the metallicity of an object is the proportion of its matter made up of Chemical elements other than Hydrogen The Big Bang is the cosmological model of the Universe that is best supported by all lines of scientific evidence and Observation. Light from these stars may have been observed in 2005 using NASA's Spitzer Space Telescope,^[3] although this observation remains to be confirmed. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program The Spitzer Space Telescope (formerly the Space Infrared Telescope Facility, SIRTF) is an Infrared Space observatory.

History of quasar observation

The first quasars were discovered with radio telescopes in the late 1950s. The 1950s Decade refers to the years of 1950 to 1959 inclusive Many were recorded as radio sources with no corresponding visible object. Using small telescopes and the Lovell Telescope as an interferometer, they were shown to have a very small angular size. The Lovell Telescope is a Radio telescope at Jodrell Bank Observatory, near Goostrey, Cheshire in the north-west of England ^[4] Hundreds of these objects were recorded by 1960 and published in the Third Cambridge Catalogue as astronomers scanned the skies for the optical counterparts. Year 1960 ( MCMLX) was a Leap year starting on Friday (link will display full calendar of the Gregorian calendar. The Third Cambridge Catalogue of Radio Sources ( 3C) is an Astronomical catalogue of celestial radio sources detected originally at 159 MHz and subsequently at In 1960, radio source 3C 48 was finally tied to an optical object. 3C48 was the first of many faint starlike quasi-stellar objects which later were named Quasars 3C48 was the first source in the Third Cambridge Astronomers detected what appeared to be a faint blue star at the location of the radio source and obtained its spectrum. Containing many unknown broad emission lines, the anomalous spectrum defied interpretation — a claim by John Bolton of a large redshift was not generally accepted. This article is on the astronomer John Bolton For other people named "John Bolton" see John Bolton (disambiguation.

In 1962 a breakthrough was achieved. Year 1962 ( MCMLXII) was a Common year starting on Monday (the link is to a full 1962 calendar of the Gregorian calendar. Another radio source, 3C 273, was predicted to undergo five occultations by the moon. 3C 273 is a Quasar located in the Constellation Virgo. It is the Optically brightest quasar in our sky ( m ~ 12 In Shia Islam The Occultation is a term used to designate the hidden state of the Imam of the Time. Measurements taken by Cyril Hazard and John Bolton during one of the occultations using the Parkes Radio Telescope allowed Maarten Schmidt to optically identify the object and obtain an optical spectrum using the 200-inch Hale Telescope on Mount Palomar. The Parkes Observatory is a Radio telescope observatory 20 kilometres north of the town of Parkes, New South Wales, Australia. Maarten Schmidt (born December 28 1929) is a Dutch Astronomer who measured the distances of astronomical objects called Quasars The Hale Telescope is the largest telescope at the Palomar Observatory, named after astronomer George Ellery Hale. This spectrum revealed the same strange emission lines. Schmidt realized that these were actually spectral lines of hydrogen redshifted at the rate of 15. 8 percent. This discovery showed that 3C 273 was receding at a rate of 47,000 km/s. ^[5] This discovery revolutionized quasar observation and allowed other astronomers to find redshifts from the emission lines from other radio sources. As predicted earlier by Bolton, 3C 48 was found to have a redshift of 37% the speed of light.

The term quasar was coined by Chinese-born U. S. astrophysicist Hong-Yee Chiu in 1964, in Physics Today, to describe these puzzling objects:

So far, the clumsily long name 'quasi-stellar radio sources' is used to describe these objects. Astrophysics is the branch of Astronomy that deals with the Physics of the Universe, including the physical properties ( Luminosity, Physics Today magazine created in 1948 is the membership journal of The American Institute of Physics. Because the nature of these objects is entirely unknown, it is hard to prepare a short, appropriate nomenclature for them so that their essential properties are obvious from their name. For convenience, the abbreviated form 'quasar' will be used throughout this paper.

– Hong-Yee Chiu in Physics Today, May, 1964

Later it was found that not all (actually only 10% or so) quasars have strong radio emission (are 'radio-loud'). Hence the name 'QSO' (quasi-stellar object) is used (in addition to 'quasar') to refer to these objects, including the 'radio-loud' and the 'radio-quiet' classes.

One great topic of debate during the 1960s was whether quasars were nearby objects or distant objects as implied by their redshift. The 1960s decade refers to the years from the beginning of 1960 to the end of 1969 In Physics and Astronomy, redshift occurs when Electromagnetic radiation – usually Visible light – emitted or reflected by It was suggested, for example, that the redshift of quasars was not due to the expansion of space but rather to light escaping a deep gravitational well. In Physics and Astronomy, redshift occurs when Electromagnetic radiation – usually Visible light – emitted or reflected by In Physics, Light or other forms of Electromagnetic radiation of a certain wavelength originating from a source placed in a region of stronger gravitational However a star of sufficient mass to form such a well would be unstable and in excess of the Hayashi limit. Hayashi limit is a constraint upon the maximum Radius of a Star for a given Mass. ^[6] Quasars also show unusual spectral emission lines which were previously only seen in hot gaseous nebulae of low density, which would be too diffuse to both generate the observed power and fit within a deep gravitational well. ^[7] There were also serious concerns regarding the idea of cosmologically distant quasars. One strong argument against them was that they implied energies that were far in excess of known energy conversion processes, including nuclear fusion. In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus At this time, there were some suggestions that quasars were made of some hitherto unknown form of stable antimatter and that this might account for their brightness. In Particle physics and Quantum chemistry, antimatter is the extension of the concept of the Antiparticle to Matter, where antimatter is composed Others speculated that quasars were a white hole end of a wormhole. In Astrophysics, a white hole is the theoretical time reversal of a Black hole. In Physics, a wormhole is a hypothetical topological feature of Spacetime that is fundamentally a 'shortcut' through Space and Time However, when accretion disc energy-production mechanisms were successfully modeled in the 1970s, the argument that quasars were too luminous became moot and today the cosmological distance of quasars is accepted by almost all researchers. An accretion disc (or accretion disk) is a structure (often a Circumstellar disk) formed by diffuse material in orbital motion around a central body This article is about the Decade 1970-1979 For the Year 1970 see 1970.

In 1979 the gravitational lens effect predicted by Einstein's General Theory of Relativity was confirmed observationally for the first time with images of the double quasar 0957+561. Year 1979 ( MCMLXXIX) was a Common year starting on Monday (link displays the 1979 Gregorian calendar) A gravitational lens is formed when the light from a very distant bright source (such as a Quasar) is "bent" around a massive object (such as a cluster of Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 The Twin Quasar (Double Quasar or Old Faithful is also known as Q0957+561, or QSO 0957+561. ^[8]

In the 1980s, unified models were developed in which quasars were classified as a particular kind of active galaxy, and a general consensus emerged that in many cases it is simply the viewing angle that distinguishes them from other classes, such as blazars and radio galaxies. The 1980s was the decade spanning from January 1 1980 to December 31 1989. A blazar is a very compact and highly variable energy source associated with a presumed Supermassive black hole at the center of a Host galaxy. Radio galaxies and their relatives radio-loud Quasars and Blazars, are types of Active galaxy that are very luminous at radio wavelengths (up The huge luminosity of quasars results from the accretion discs of central supermassive black holes, which can convert on the order of 10% of the mass of an object into energy as compared to 0. An accretion disc (or accretion disk) is a structure (often a Circumstellar disk) formed by diffuse material in orbital motion around a central body Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός 7% for the p-p chain nuclear fusion process that dominates the energy production in sun-like stars. In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus

This mechanism also explains why quasars were more common in the early universe, as this energy production ends when the supermassive black hole consumes all of the gas and dust near it. This means that it is possible that most galaxies, including our own Milky Way, have gone through an active stage (appearing as a quasar or some other class of active galaxy depending on black hole mass and accretion rate) and are now quiescent because they lack a supply of matter to feed into their central black holes to generate radiation.

Further reading

• Melia, Fulvio, The Edge of Infinity. Fulvio Melia (born 2 August 1956) is an Italian - American Physicist / Astrophysicist and Author. Supermassive Black Holes in the Universe 2003, Cambridge University Press, ISBN 978-0-521-81405-8 (Cloth)

See also

• Active galactic nuclei (AGN)
• Blazar
• List of quasars
• Optically Violently Variable (OVV) quasars
• Supermassive black hole
• Microquasar

References

• Complete Cosmos - Discovery Science Channel

External links

• 3C 273, the brightest quasar
• 3C 273: Variable Star Of The Season
• SKY-MAP.ORG SDSS image of quasar 3C 273
• Expanding Gallery of Hires Quasar Images
• Gallery of Quasar Spectra from SDSS
• SDSS Advanced Student Projects: Quasars
• Black Holes: Gravity's Relentless Pull Award-winning interactive multimedia Web site about the physics and astronomy of black holes from the Space Telescope Science Institute
• Research Sheds New Light On Quasars (SpaceDaily) July 26, 2006