What is a quasar?

Answer 1

A quasar (contraction of QUASi-stellAR radio source) is an astronomical source of electromagnetic energy, including light. Quasars visible from Earth all show a very high redshift. The scientific consensus is that this high redshift is the result of the high going away speed that, when combined with Hubble's law, means that the quasars are very distant. To be observable at that distance, the energy output of quasars must dwarf that of almost every known astrophysical phenomenon with the exception of comparatively short-lived supernovae and gamma-ray bursts. They may readily release energy in levels equal to the output of hundreds of average galaxies combined. The output of light is equivalent to one trillion suns.

In optical telescopes, most quasars look like single points of light (i.e. point source) although some are seen to be the centers of active galaxies. Most quasars are too faint to be seen with small telescopes, but 3C 273, with an average apparent magnitude of 12.9, is an exception. At a distance of 2.44 billion light years, it is one of the most distant objects directly observable with amateur equipment.

Some quasars display rapid changes in luminosity, which implies that they are small (an object cannot change faster than the time it takes light to travel from one end to the other; but see quasar J1819+3845 for another explanation). The highest redshift currently known for a quasar is 6.4. [1]

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. No other currently known mechanism appears able to explain the vast energy output and rapid variability.

Knowledge of quasars is advancing rapidly. As recently as the 1980s, there was no clear consensus as to their origin.

More than 100,000 quasars are known. All observed spectra have shown considerable redshifts, ranging from 0.06 to the recent maximum of 6.4. Therefore, all known quasars lie at great distances from us, the closest being 240 Mpc (780 million ly) away and the farthest being 4 Gpc (13 billion ly) away. Most quasars are known to lie above 1.0 Gpc in distance; since light takes such a long time to cover these great distances, we are seeing quasars as they existed long ago — the universe as it was in the distant past.

Although faint when seen optically, their high redshift implies that these objects lie at a great distance from us, making quasars the most luminous objects in the known universe. The quasar which appears brightest in our sky is the ultraluminous 3C 273 in the constellation of Virgo. It has an average apparent magnitude of 12.8 (bright enough to be seen through a small telescope), but it has an absolute magnitude of −26.7. So from a distance of 10 parsecs (about 33 light-years), this object would shine in the sky about as bright as our sun. 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.

The hyperluminous quasar APM 08279+5255 was, when discovered in 1998, given an absolute magnitude of −32.2, although high resolution imaging with the Hubble Space Telescope and the 10 m Keck Telescope reveal that this system is gravitationally lensed. 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. HS 1946+7658 was thought to have an absolute magnitude of −30.3, but this too was magnified by the gravitational lensing effect.

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 evidence has allowed scientists to theorize 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.

Quasars exhibit many of the same properties as active galaxies: Radiation is nonthermal and some are observed to have jets and lobes like those of radio galaxies. Quasars can be observed in many parts of the electromagnetic spectrum including radio, infrared, optical, ultraviolet, X-ray and even gamma rays. Most quasars are brightest in their rest-frame near-ultraviolet (near the 1216 angstrom (121.6 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 0.9 µm), in the near infrared.

Iron Quasars show strong emission lines resulting from ionised iron, such as IRAS 18508-7815.

Answer 2

A quasar (contraction of QUASi-stellAR radio source) is an astronomical source of electromagnetic energy, including light, which shows a very high redshift. The scientific consensus is that this high redshift is the result of Hubble's law. This implies that quasars are very distant. To be observable at that distance, the energy output of quasars must dwarf that of almost every known astrophysical phenomenon with the exception of comparatively short-lived supernovae and gamma-ray bursts. They may readily release energy in levels equal to the output of hundreds of average galaxies combined. The output of light is equivalent to one trillion suns.

In optical telescopes, most quasars look like single points of light (i.e. point source) although some are seen to be the centers of active galaxies.

Some quasars display rapid changes in luminosity, which implies that they are small (an object cannot change faster than the time it takes light to travel from one end to the other; but see [[quasar J1819+3845]] for another explanation). The highest redshift currently known for a quasar is 6.4.

Answer 3

A quasar (contraction of QUASi-stellAR radio source) is an astronomical source of electromagnetic potential, jointly with ordinary, which shows an particularly severe redshift. The medical consensus is this severe redshift is the end results of Hubble's regulation. this suggests that quasars are very distant. To be observable at that distance, the potential output of quasars could dwarf that of rather a lot each familiar astrophysical phenomenon except for rather short-lived supernovae and gamma-ray bursts. they could only launch potential in degrees equivalent to the output of thousands of everyday galaxies mixed. In optical telescopes, maximum quasars look like unmarried factors of light (i.e. aspect source) regardless of the truth that some are seen to be the centers of lively galaxies. some quasars exhibit speedy adjustments in luminosity, meaning that they are small (an merchandise can't replace swifter than the time it takes ordinary to commute from one end to the different; yet see quasar Jc4ca4238a0b92382dcc509a6f75849b8c4ca4238a0b92382dcc509a6f75849b9+3845 for yet another rationalization). the optimal redshift at the moment familiar for a quasar is 6.4. [a million] Quasars are believed to be powered by technique of accretion of fabrics onto supermassive black holes contained in the nuclei of distant galaxies, making those luminous variations of the final classification of gadgets familiar as lively galaxies. No different at the moment familiar mechanism looks able to describe the massive potential output and speedy variability. understand-how of quasars is advancing without delay. As at the moment because the c4ca4238a0b92382dcc509a6f75849b990's there became no clean consensus as to their starting place. you are able to get more suitable recommendations from the link below...

Answer 4

Quasar is shorthand for "quasi-stellar object", a very bright-burning galaxy from the early years of the Universe. They burned out very fast, so they threw off a lot of light and then exploded. Since they were so bright, they are the oldest star-like objects visible, hence their name.

Answer 5

http://en.wikipedia.org/wiki/Quasar

a quasar is essentially a galactic nucleus where a supermassive black hole is is acceding a lot of matter, and in the process, the black hole spews most of the matter away with a lot of energy. active quasars are so bright that they can be seen at much larger distances than if they inactive.