A major concern was the enormous amount of energy these objects would have to be radiating, if they were distant.
In the s no commonly-accepted mechanism could account for this. The currently accepted explanation, that it was due to matter in an accretion disc falling into an supermassive black hole, was only suggested in by Salpeter and Yakov Zel'dovich ,  and even then it was rejected by many astronomers, because the existence of black holes was still widely seen as theoretical and too exotic, in the s, and because it was not yet confirmed that many galaxies including our own have supermassive black holes at their center.
The strange spectral lines in their radiation, and the speed of change seen in some quasars, also suggested to many astronomers and cosmologists that the objects were comparatively small and therefore perhaps bright, massive and not far away; accordingly that their redshifts were not due to distance or velocity, and must be due to some other reason or an unknown process, meaning that the quasars were not really powerful objects nor at extreme distances, as their redshifted light implied.
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.
Various explanations were proposed during the s and s, each with their own problems. It was suggested that quasars were nearby objects, and that their redshift was not due to the expansion of space general relativity but rather to light escaping a deep gravitational well special relativity.
This would require a massive object, which would also explain the high luminosities. However a star of sufficient mass to produce the measured redshift would be unstable and in excess of the Hayashi limit.
One strong argument against them was that they implied energies that were far in excess of known energy conversion processes, including nuclear fusion.
There were some suggestions that quasars were made of some hitherto unknown form of stable antimatter regions and that this might account for their brightness.
The uncertainty was such that even as late as , it was stated that "one of the few statements [about Active Galactic Nuclei] to command general agreement has been that the power supply is primarily gravitational",  with the cosmological origin of the redshift being taken as given.
Eventually, starting from about the s, 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.
This model also fits well with other observations that suggest many or even most galaxies have a massive central black hole.
It would also explain why quasars are more common in the early universe: The accretion disc energy-production mechanism was finally modeled in the s, and black holes were also directly detected including evidence showing that supermassive black holes could be found at the centers of our own and many other galaxies , which resolved the concern that quasars were too luminous to be a result of very distant objects or that a suitable mechanism could not be confirmed to exist in nature.
By it was "well accepted" that this was the correct explanation for quasars,  and the cosmological distance and energy output of quasars was accepted by almost all researchers.
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.
The discovery of the quasar had large implications for the field of astronomy in the s, including drawing physics and astronomy closer together.
It is now known that quasars are distant but extremely luminous objects, so any light which reaches the Earth is redshifted due to the metric expansion of space.
Quasars inhabit the center of active galaxies, and are among the most luminous, powerful, and energetic objects known in the universe, emitting up to a thousand times the energy output of the Milky Way , which contains — billion stars.
This radiation is emitted across the electromagnetic spectrum, almost uniformly, from X-rays to the far-infrared with a peak in the ultraviolet-optical bands, with some quasars also being strong sources of radio emission and of gamma-rays.
With high-resolution imaging from ground-based telescopes and the Hubble Space Telescope , the "host galaxies" surrounding the quasars have been detected in some cases.
Most quasars, with the exception of 3C whose average apparent magnitude is Quasars are believed - and in many cases confirmed - to be powered by accretion of material into supermassive black holes in the nuclei of distant galaxies, as suggested in by Edwin Salpeter and Yakov Zel'dovich .
Light and other radiation cannot escape from within the event horizon of a black hole, but the energy produced by a quasar is generated outside the black hole, by gravitational stresses and immense friction within the material nearest to the black hole, as it orbits and falls inward.
Central masses of 10 5 to 10 9 solar masses have been measured in quasars by using reverberation mapping.
Several dozen nearby large galaxies, including our own Milky Way galaxy, that do not have an active center and do not show any activity similar to a quasar, are confirmed to contain a similar supermassive black hole in their nuclei galactic center.
Thus it is now thought that all large galaxies have a black hole of this kind, but only a small fraction have sufficient matter in the right kind of orbit at their center to become active and power radiation in such a way to be seen as quasars.
This 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 the Milky Way, have gone through an active stage, appearing as a quasar or some other class of active galaxy that depended on the black hole mass and the accretion rate, and are now quiescent because they lack a supply of matter to feed into their central black holes to generate radiation.
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 into an accretion disc.
Quasars may also be ignited or re-ignited when normal galaxies merge and the black hole is infused with a fresh source of matter.
In fact, it has been suggested that a quasar could form when the Andromeda Galaxy collides with our own Milky Way galaxy in approximately 3—5 billion years.
In the s, 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.
More than , quasars are known, most from the Sloan Digital Sky Survey. All observed quasar spectra have redshifts between 0. Applying Hubble's law to these redshifts, it can be shown that they are between million  and Because of the great distances to the farthest quasars and the finite velocity of light, they and their surrounding space appear as they existed in the very early universe.
The power of quasars originates from supermassive black holes that are believed to exist at the core of most galaxies.
The Doppler shifts of stars near the cores of galaxies indicate that they are rotating around tremendous masses with very steep gravity gradients, suggesting black holes.
Although quasars appear faint when viewed from Earth, they are visible from extreme distances, being the most luminous objects in the known universe.
It has an average apparent magnitude of In a universe containing hundreds of billions of galaxies, most of which had active nuclei billions of years ago but only seen today, it is statistically certain that thousands of energy jets should be pointed toward the Earth, some more directly than others.
In many cases it is likely that the brighter the quasar, the more directly its jet is aimed at the Earth. Such quasars are called blazars.
Quasars were much more common in the early universe than they are today. This discovery by Maarten Schmidt in was early strong evidence against Steady State cosmology and in favor of the Big Bang cosmology.
Quasars show the locations 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 jets, radiation and winds created by the 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 those clusters from cooling and falling onto the central galaxy.
Quasars' luminosities are variable, with time scales that range from months to 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 as to allow the coordination of the luminosity variations.
This would mean that a quasar varying on a 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 than the nuclear fusion that powers stars.
Stellar explosions such as supernovas and gamma-ray bursts , and direct matter - antimatter annihilation, can also produce very high power output, but supernovae only last for days, and the universe does not appear to have had large amounts of antimatter at the relevant times.
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.
The brightest known quasars devour solar masses of material every year. The largest known is estimated to consume matter equivalent to Earths per minute.
Quasar luminosities can vary considerably over time, depending on their surroundings. Since it is difficult to fuel quasars for many billions of years, after a quasar finishes accreting the surrounding gas and dust, it becomes an ordinary galaxy.
Radiation from quasars is partially 'nonthermal' i. Extremely high energies might be explained by several mechanisms see Fermi acceleration and Centrifugal mechanism of acceleration.
Quasars can be detected over the entire observable electromagnetic spectrum including radio , infrared , visible light , ultraviolet , X-ray and even gamma rays.
Most quasars are brightest in their rest-frame near-ultraviolet wavelength of A minority of quasars show strong radio emission, which is generated by jets of matter moving close to the speed of light.
When viewed downward, these appear as blazars and often have regions that seem to move away from the center faster than the speed of light superluminal expansion.
This is an optical illusion due to the properties of special relativity. Quasar redshifts are measured from the strong spectral lines that dominate their visible and ultraviolet emission spectra.
These lines are brighter than the continuous spectrum. They exhibit Doppler broadening corresponding to mean speed of several percent of the speed of light.
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.
The atoms emitting these lines range from neutral to highly ionized, leaving it highly charged. This wide range of ionization shows that the gas is highly irradiated by the quasar, not merely hot, and not by stars, which cannot produce such a wide range of ionization.
Like all unobscured active galaxies, quasars can be strong X-ray sources. Radio-loud quasars can also produce X-rays and gamma rays by inverse Compton scattering of lower-energy photons by the radio-emitting electrons in the jet.
Quasars also provide some clues as to the end of the Big Bang 's reionization. More recent quasars show no absorption region but rather their spectra contain a spiky area known as the Lyman-alpha forest ; this indicates that the intergalactic medium has undergone reionization into plasma , and that neutral gas exists only in small clouds.
The intense production of ionizing ultraviolet radiation is also significant, as it would provide a mechanism for reionization to occur as galaxies form.
Quasars 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.
Light from these stars may have been observed in using NASA 's Spitzer Space Telescope ,  although this observation remains to be confirmed. The taxonomy of quasars includes various subtypes representing subsets of the quasar population having distinct properties.
Because quasars are extremely distant, bright, and small in apparent size, they are useful reference points in establishing a measurement grid on the sky.
Because they are so distant, they are apparently stationary to our current technology, yet their positions can be measured with the utmost accuracy by very-long-baseline interferometry VLBI.
The positions of most are known to 0. A multiple-image quasar is a quasar whose light undergoes gravitational lensing , resulting in double, triple or quadruple images of the same quasar.
As quasars are rare objects, the probability of three or more separate quasars being found near the same location is very low.
The first true triple quasar was found in by observations at the W. Keck Observatory Mauna Kea , Hawaii. When astronomers discovered the third member, they confirmed that the sources were separate and not the result of gravitational lensing.
The first quadruple quasar was discovered in When two quasars are so nearly in the same direction as seen from Earth that they appear to be a single quasar but may be separated by the use of telescopes, they are referred to as a "double quasar", such as the Twin Quasar.
This configuration is similar to the optical double star. Two quasars, a "quasar pair", may be closely related in time and space, and be gravitationally bound to one another.
Depending on this angle, different quasar components—the accretion disk, emission-line clouds, jets—appear to be more or less prominent.
This results in a wide variety of observed phenomena from what are, in reality, physically similar sources. Because of the finite speed of light , when quasars are observed at great distances, they are observed as they were in the distant past.
Thus, the increasing density of quasars with distance means that they were more common in the past than they are now.
At earlier ages, the number density of quasars decreases sharply, corresponding to an era when the quasar population was still building up.
The most distant, and thus earliest, quasars known were formed less than a billion years after the big bang. Individual quasars appear as their central black holes begin to accrete gas at a high rate, possibly triggered by a merger with another galaxy, building up the mass of the central black hole.
The current best estimate is that quasar activity is episodic, with individual episodes lasting around a million years and the total quasar lifetime lasting around 10 million years.
At some point, quasar activity ceases completely, leaving behind the dormant massive black holes found in most massive galaxies.
Indeed, in the current universe the remaining AGN population is made up predominantly of lower-luminosity Seyfert galaxies with relatively small supermassive black holes.
In the present-day universe there is a close relationship between the mass of a black hole and the mass of its host galaxy. This is quite remarkable, since the central black hole accounts for only about 0.
It is believed that the intense radiation, mass outflows, and jets from the black hole during its active quasar phase are responsible.
The radiation, outflows, and jets heat up and can even remove entirely the interstellar medium from the host galaxy. We welcome suggested improvements to any of our articles.
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QSO, quasi-stellar radio source. Learn More in these related Britannica articles: The discovery of quasars quasi-stellar radio sources in the early s also told heavily against the steady-state theory.
Quasar s were first identified as strong radio sources that in visible light appear to be identified with small starlike objects.
Further, they have large redshifts, which implies that they are…. Quasar s are objects whose spectra display very large redshifts, thus implying in accordance with the Hubble law that they lie at the greatest distances see above Determining astronomical distances.
They were discovered in but remained enigmatic for many years. They appear as starlike i. These cosmic objects have intense clouds of radio emission that extend hundreds of thousands of light-years away from a central energy source located in an active galactic nucleus AGN , or quasar.
Observations with high-resolution radio arrays show…. Luminosity , in astronomy, the amount of light emitted by an object in a unit of time.
The luminosity of the Sun is 3. Quasars active galaxies In active galactic nucleus classification of galaxies In galaxy: Other classification schemes and galaxy types history of astronomy In astronomy: The steady-state challenge luminosity In galaxy: Luminosity observational astronomy In astronomy: Study of other galaxies and related phenomena radio sources In radio and radar astronomy In radio source radio telescopes In radio telescope: Major applications of radio telescopes redshift In redshift View More.
Articles from Britannica Encyclopedias for elementary and high school students. Help us improve this article!
Contact our editors with your feedback. Introduction Discovery of quasars Finding quasars Physical structure of quasars Evolution of quasars.
You may find it helpful to search within the site to see how similar or related subjects are covered. Any text you add should be original, not copied from other sources.The first quasars 3C 48 and 3C were discovered in the late s, as radio sources in all-sky radio surveys. On January 11,the discovery of the Huge-LQG was announced by the University of Central Lancashireas the largest known structure in the universe by that time. At earlier ages, the number density of quasars decreases sharply, corresponding to an Beste Spielothek in Malmeneich finden when the quasar population was still building up. Schmidt was able to demonstrate that these were likely to be the ordinary spectral lines of hydrogen redshifted by By it was "well accepted" that this was the correct explanation casino delmenhorst quasars, Beste Spielothek in Nordstemmen finden and the cosmological distance and energy output of quasars was accepted by almost all researchers. When two quasars are so nearly in the same direction as seen from Earth that they appear to be a single quasar but may be separated by the use of telescopes, they are referred to as a "double quasar", such as the Twin Quasar. Help us improve this article! Retrieved from " https: It is robredo that the intense radiation, mass outflows, and jets from the black hole during its active quasar phase are responsible. Quasaran astronomical object of very high luminosity found in the centres of some galaxies Beste Spielothek in Ulbargen finden powered by gas spiraling at high velocity into an extremely gonewild black hole.