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As gas in the disk falls towards the black hole, energy is released in the form of electromagnetic radiation , which can be observed across the electromagnetic spectrum.
The power radiated by quasars is enormous: the most powerful quasars have luminosities thousands of times greater than a galaxy such as the Milky Way.
The redshifts of quasars are of cosmological origin. The term quasar originated as a contraction of quasi-stellar [star-like] radio source , because quasars were first identified during the s 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.
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.
Quasars are found over a very broad range of distances, and quasar discovery surveys have demonstrated that quasar activity was more common in the distant past.
The peak epoch of quasar activity was approximately 10 billion years ago. The supermassive black hole in this quasar, estimated at million solar masses , is the most distant black hole identified to date.
The term "quasar" was first used in an article by Chinese-American astrophysicist Hong-Yee Chiu in May , in Physics Today , to describe certain astronomically-puzzling objects: .
So far, the clumsily long name "quasi-stellar radio sources" is used to describe these objects. 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. Between and , it became clear from work by Heber Curtis , Ernst Öpik and others, that some objects " nebulae " seen by astronomers were in fact distant galaxies like our own.
But when radio astronomy commenced in the s, astronomers detected, among the galaxies, a small number of anomalous objects with properties that defied explanation.
The objects emitted large amounts of radiation of many frequencies, but no source could be located optically, or in some cases only a faint and point-like object somewhat like a distant star.
The spectral lines of these objects, which identify the chemical elements of which the object is composed, were also extremely strange and defied explanation.
Some of them changed their luminosity very rapidly in the optical range and even more rapidly in the X-ray range, suggesting an upper limit on their size, perhaps no larger than our own Solar System.
They were described as "quasi-stellar [meaning: star-like] radio sources" , or "quasi-stellar objects" QSOs , a name which reflected their unknown nature, and this became shortened to "quasar".
Using small telescopes and the Lovell Telescope as an interferometer, they were shown to have a very small angular size. In , a definite identification of the radio source 3C 48 with an optical object was published by Allan Sandage and Thomas A.
Astronomers had detected what appeared to be a faint blue star at the location of the radio source and obtained its spectrum, which contained many unknown broad emission lines.
The anomalous spectrum defied interpretation. British-Australian astronomer John Bolton made many early observations of quasars, including a breakthrough in 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 inch 5.
This spectrum revealed the same strange emission lines. Schmidt was able to demonstrate that these were likely to be the ordinary spectral lines of hydrogen redshifted by Although it raised many questions, Schmidt's discovery quickly revolutionized quasar observation.
Shortly afterwards, two more quasar spectra in and five more in were also confirmed as ordinary light that had been redshifted to an extreme degree.
An extreme redshift could imply great distance and velocity but could also be due to extreme mass or perhaps some other unknown laws of nature.
Extreme velocity and distance would also imply immense power output, which lacked explanation. The small sizes were confirmed by interferometry and by observing the speed with which the quasar as a whole varied in output, and by their inability to be seen in even the most powerful visible-light telescopes as anything more than faint starlike points of light.
But if they were small and far away in space, their power output would have to be immense and difficult to explain. Equally, if they were very small and much closer to our galaxy, it would be easy to explain their apparent power output, but less easy to explain their redshifts and lack of detectable movement against the background of the universe.
Schmidt noted that redshift is also associated with the expansion of the universe, as codified in Hubble's law. If the measured redshift was due to expansion, then this would support an interpretation of very distant objects with extraordinarily high luminosity and power output, far beyond any object seen to date.
This extreme luminosity would also explain the large radio signal. He stated that a distant and extremely powerful object seemed more likely to be correct.
Schmidt's explanation for the high redshift was not widely accepted at the time. 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 is due to matter in an accretion disc falling into a supermassive black hole , was only suggested in by Edwin Salpeter and Yakov Zel'dovich ,  and even then it was rejected by many astronomers, because in the s, the existence of black holes was still widely seen as theoretical and too exotic, 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 special relativity but rather to light escaping a deep gravitational well general 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.
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 suggesting that many or even most galaxies have a massive central black hole.
It would also explain why quasars are more common in the early universe: as a quasar draws matter from its accretion disc, there comes a point when there is less matter nearby, and energy production falls off or ceases, as the quasar becomes a more ordinary type of galaxy.
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, further categorised into 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 that reaches the Earth is redshifted due to the metric expansion of space.
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.
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.
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 as 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, which 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 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 have been found  , 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 by 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 10 Earths per second.
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 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.
With ever more weighty outer layers becoming more compact due to the heavier elements formed there through fusion the stellar core can no longer carry that weight and the free electrons in the core are forced into the nuclei of iron leading to neutronization.
The stellar core collapses dBS Ch. Perhaps astonishing: A black hole is born The first quasars "quasi stellar radiosources" were discovered in the late s in all-sky radio surveys see Wikipedia.
And "quasi stellar objects" were found in the optical. Maarten Schmidt obtained the first optical spectrum of a QSO in Soon it became clear that these types of object are very similar and then generally were named quasar.
Quasars emit gigantic amounts of radiation, sometimes more than all radiation from one large galaxy. This makes clear, that quasars can be seen even in the far reaches of the universe.
With infrared telescopes and the Hubble Space Telescope, the "host galaxies" surrounding the quasars have been detected in some cases.
These galaxies are normally too dim to be seen against the glare of the quasar, except with special techniques Wikipedia.
X-Ray astronomical measurements revealed also that the centres of some galaxies were bright in X-Ray radiation. In addition, such centres showed numerous spectral structures in the visual spectra signifying the emission of light from highly excited atoms and ions.
Artist's impression of a quasar. A supermassive black hole is surrounded by a disk of material being drawn in. Two polar jets spew highly energized material outward.
Image: Carnegie Institution for Science. The radiation from a quasar comes mostly as a smooth continuum over all wavelengths, signifying it emerges in a very hot plasma.
The accepted model of a quasar is an exceedingly heavy black hole surrounded by a disk of material, falling into the black hole's potential well.
This falling in means also rotation, so a disk is formed and the inner side of this disk rotates extremely fast, leading to an accretion disk image.
Due to the twisting of the magnetic fields, some of that very hot material is ejected perpendicular to the disk, in polar jets. The centre of the Milky Way had been investigated for decades but dust in the intervening gas had obscured our view.
After devices measuring at near-infrared wavelengths had been developed IR-radiation is hardly affected by dust , the centre of the Milky Way could be seen.
Soon one found stars zipping around that very centre. So our Milky Way is, also in this sense, not an exceptional galaxy.
Really measuring distances in the Universe is neigh to impossible. Astronomers have found ways around this problem.
They have devised appropriate "yardsticks" to that end. Details can be found in determining distances in German.
One starts with stars. Beginning with the parallactic method, geometric distances to nearby stars could be determined.
It led to the definition of a "parsec" pc , the distance of a star showing one second of arc in parallax. This distance equals 3.
With these nearby stars one could calibrate the intrinsic amount of light emitted by these stars. Together with spectroscopic information, this classified the stars rather precisely.
Understanding stars, one trusted the spectroscopic information to be sufficient for classification. Then, noting of a star the actual small amount of light received in comparison with what such a star would radiate, one could calculate its distance.
As soon as one knew enough stars, one recognised that some variable stars stars rhythmically varying the amount of emitted light always had an intrinsic brightness within some limits.
Seeing little light of such a star meant it must be far away, yet its distance could be calculated. For this technique the intrinsically bright Cepheid variable stars could be used to even reach neighbouring galaxies.
Edwin Hubble, extending earlier observations, showed in with the help of Cepheid stars that the farther away a galaxy is, the faster it receedes from us.
This receeding is found from the spectrum of galaxies: absorption structures in their spectra are shifted toward the red, the so-called red shift. This led to the notion of an expanding universe.
The measurements of Cepheid stars in galaxies with the Hubble Space Telescope calibrated this expansion in the nearby part of the universe, in that part, in which the HST could spatially recognise those Cepheids.
These supernovae are the explosion of a white dwarf star in a binary star system, an explosion occurring once the star accreting matter from its neighboor reaches a mass of 1.
This through physics well defined mass suggested all these supernovae are the same, thus becoming equally bright, thereby providing a yardstick reaching to much larger distances than the Cepheid stars.
Finally, if one trusts the relation for the expansion of the universe, one can use the red-shift observed in the spectrum of a galaxy to calculate its distance.
Thus, in fact, the yardstick for the far away reaches of the universe is the red-shift. Astronomers accept this all; deep down they know not all need be perfect, but there is nothing better.
The distance of a far away quasar is derived from the observed red-shift of features in its spectrum. Note that, if a quasar is very far away, its spectrum is considerably red-shifted.
This means that features normally appearing at visual wavelegths get stretched by the expansion of the universe into the infrared.
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Quasar Black Hole VideoBlack Hole Size Comparison 2019
Prior to the launch of Hubble a handful of black hole candidates had been studied but the limitations of ground based astronomy were such that irrefutable evidence for their existence could not be obtained.
Black holes themselves, by definition, cannot be observed, since no light can escape from them. However, astronomers can study the effects of black holes on their surroundings.
These include powerful jets of electrons that travel huge distances, many thousands of light years from the centres of the galaxies.
Matter falling towards a black hole can also be seen emitting bright light and if the speed of this falling matter can be measured , it is possible to determine the mass of the black hole itself.
This is not an easy task and it requires the extraordinary capabilities of Hubble to carry out these sophisticated measurements.
Hubble observations have been fundamental in the study of the jets and discs of matter around a number of black holes.
Accurate measurements of the masses have been possible for the first time. Hubble has found black holes 3 billion times as massive as our Sun at the centre of some galaxies.
While this might have been expected, Hubble has surprised everyone by providing strong evidence that black holes exist at the centres of all large galaxies and even small galaxies.
Hubble also managed not only to observe the jets created by black holes but also the glowing discs of material surrounding a supermassive black hole.
Furthermore, it appears that larger galaxies are the hosts of larger black holes. There must be some mechanism that links the formation of the galaxy to that of its black hole and vice versa.
This has profound implications for theories of galaxy formation and evolution and is an ongoing area of research in astronomy. UTC Offset:.
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Groups Why Join? Astronomy Day. Cosmos: Origin and Fate of the Universe. Astronomy's Ganymede Globe. The quasar 3C appears starlike in this optical image taken by the Hubble Space Telescope.
In reality, the light comes from the accretion disk around a supermassive black hole. The disk is so bright that the galaxy around it cannot be seen.
There is a black hole behind every quasar, but not every black hole is a quasar. So yes, in a way, a quasar is simply one face a black hole may show.
If you are looking at a quasar, you are absolutely looking at a black hole. How Did Quasars Form? Earth-space telescope system produces hot surprise.
Active Galactic Nucleus AGN galaxies all have a very powerful energy source much bigger than what ordinary stars produce including supernovas and neutron stars coming from a small area in the center of their galaxies.
These quasars are now recognized as super massive black holes at the center of emerging galaxies "back in the early universe". The quasar is believed to be powered by the accretion disc around the centralized black hole.
Note that the quasar's radiation comes from the edge of the accretion disc, rather than from the accretion disk's center, which is also the center of the black hole.
Most quasar radiation exceeds the luminous output of average size galaxies. However, they appear star-like in ordinary telescopic photographs because the light from their nucleus dominates the light from the surrounding galaxy.
Quasars are the most luminous, powerful, and energetic objects in the universe. They inhabit the centers of very young active galaxies and emit up to a thousand times the energy output of our whole Milky Way and two trillion times the energy of our sun.
Most quasars have a very high redshift the measurement of the stretching of light to the red end of the spectrum by the expansion of the universe.
The implication of the large redshift is that quasars are very distant, meaning they are objects from much earlier in the universe's history.
Most were born when the universe was less than 5 billion years old, at a redshift of 1. Quasars are about the same size as our Solar System i. This implies a humongous energy density.
The brightest known quasars devour 1, solar masses every year. Shown at the left and also the jet directly below is the first and brightest quasar visible from earth - 3c Galaxy 3c is located in the Orion Constellation, but is about 2.
Since light cannot escape the super massive black holes that are at the center of quasars, the escaping light is actually generated outside the event horizon of the black hole by extreme twisting magnetic forces and the immense friction of incoming material.
Most of the material falling into the central black hole's gravity field is unlikely to fall directly into the black hole, but rather into the accretion disk surrounding the black hole.
The falling matter will have some angular momentum of its own that will add to the angular momentum of the accretion disc so that total angular momentum is conserved.
Several dozen nearby large galaxies have been shown to contain a central black hole in their nuclei with no sign of a quasar nucleus.
It is thought that all large galaxies have a super-massive black hole at their center, but only a small fraction emit powerful radiation and are seen as quasars.
Many scientists contend that most supermassive black holes today were once quasars in the early universe.
As the quasars fuel was depleted they become the supermassive black holes that we observe today. Some become almost dormant for lack of fuel, for example: the black hole in the center of the Milky Way.
Scientists believe quasars may be re-ignited from dormant galaxies if they ingest a fresh source of gas or other matter. The spectra of quasars are quite different from those of ordinary galaxies showing broad emission lines of gas excited to high levels.
They also exhibit a blue continuous spectrum lacking the absorption lines from ordinary stars. The beams of radiation from material moving close to the speed of light indicates that the jet's light has been boosted such that it overwhelms everything else.
The quasar's luminosity is variable at nearly every wavelength from radio waves to gamma-rays on time scales of a few days to decades.
Also, the variability in light output indicates that most of the radiation is coming from tiny regions, no more than a few light hours in size.
The scale on the bottom of the chart is time, but it can also be redshift as shown at the top of the chart. Looking at very distant objects in the universe is equivalent to looking back in time because of the constant speed of light in a vacuum.
The number of quasars peaks at a redshift of about 2. At a redshift of about 4. About this time early galaxies formed, collected enough material to make a fairly massive black hole, and had enough massive stars in its immediate neighborhood to devour and produce the heavy elements seen in quasar spectra.
The first stars, forming from pure hydrogen and helium, were quite different from the ones we see today.
The first stars were very massive and hot, exploding with more violence than today's supernovae. These stars, with masses hundreds of times larger than our sun, would have scattered their make up of heavier elements very widely as each exploded.
These explosions would have destroyed the surrounding gas clouds and forced galaxy formation to start over.
The great abundance of quasars in the early universe is consistent with the notion that a quasar shuts off when its black hole engine has consumed the fuel surrounding the host galaxy.
In the early universe there most likely was more mass mostly gas accessible to black holes than today because much of it has already been consumed.
As the hungry black holes of the early quasars ran out of local fuel, they eventually shut down.
Today there are vast voids between galaxies and little food for the massive black holes. This has caused most of the quasars to be dormant for some time.
To see a lot of burning quasars, we have to look a considerable way back in time. Quasars, the brightest objects in the universe, can be used as research tools to study objects in the distant universe through gravitational lensing and other techniques.
One of the successes of Einstein's general theory of relativity was the prediction of the "bending of light" by a massive object such as the sun.