In Astronomy, a Quasar (for quasi-stellar radiation source , quasi-stellar radio source in English) is an electromagnetic source of energy, including the Lumière. The visible quasars of the Ground show a whole a very high redshift. The scientific consensus said that a high redshift is the result of the Loi of Hubble, i.e. the quasars are very distant. To be observable at this distance, energy that release the quasars must be reduced to a phenomenon known Astrophysique, mainly the Supernova E and the starts gamma (which have a relatively short life). They can release as much from energy than hundreds of combined Galaxies. Released luminous energy is equivalent to that which would be released by 10 12 Sun S.
With the Telescope S optics, the majority of the quasars resemble small luminous points, although some are seen as being the centers of active galaxies (couramments known under abbreviation AGN, for Active Galaxy Nucleus). The majority of the quasars are too much distant to be seen with small telescopes, but 3C 273, with a Magnitude connect (or relative) of 12,9, is an exception. At a distance of 2,44 billion light-years, it is one of the only observable remote objects with equipment of amateur.
Certain quasars show rapids changes of luminosity, which implies that they are rather small (an object cannot change more quickly than time than it is necessary for the light to travel of an end to the other; to see the article on the quasar J1819+3845 for another explanation). Currently (February 2007), the redshift highest ever recorded for a quasar is 6,4.
It is thought that the quasars gain in power by accretion of Matière around the black holes supermassifs which are in the core of these galaxies, making “luminous versions” of these objects known as being active galaxies. No other mechanism appears able to explain immense released energy and their rapid variability.
The knowledge of the quasars advances quickly. In the years 1980, it had no consensus there on their origin.
One counts more than 100.000 quasars. All the spectrum S observed show redshifts going from 0,06 to 6,4. Consequently, all the known quasars are located at very long distances from us, nearest to us being with 240 mégaparsecs (~ 780 million light-years) and most distant being to four gigaparsecs (~ 13 billion Al), with the limits of the observable universe. As the light takes much time to cover these long distances, the majority of the quasars which are beyond 1,0 gigaparsec of distance are seen such as they existed in a very remote past of the Univers, their light reaching us only today.
Though weak when they are optically observed (their redshift high implies that these objects are very distant from us) the quasars are the most brilliant objects known in the Universe. The quasar which appears most brilliant in our sky is the hyper-luminous 3C 273, in the Constellation of the Vierge. It has an apparent magnitude of approximately 12,9 (enough shining to be seen with a small telescope) but its absolute Magnitude is of -26,7. That wants to say that at a distance from 10 PC (~ 33 al), this object would as strongly shine in the sky as our Sun. The luminosity of this quasar is thus 2 × 10 12 time stronger than that of our Sun, or approximately 100 times stronger than the total light of a giant galaxy, such as our Milky Way.
The super-luminous quasar APM 08279+5255 had, when one discovered it in 1998, an absolute magnitude of -32,2, though the images with high-resolution of the telescopes Hubble and Keck reveal that this system is gravitationally enlarged. A study of the gravitational enlargement in this system suggests that it at summer amplified by a factor from approximately 10. That is still much more luminous than the very close quasars such as 3C 273. It was thought that HS 1946+7658 had an absolute magnitude of -30,3, but he also was emphasized by the effect of gravitational enlargement.
It was discovered that the quasars varied in luminosity on various scales of time. Some vary in brightness all the X month, weeks, days, or hours. This discovery allowed to the scientists to theorize the fact that the quasars generate and emit their energy in a small area, since each part of quasar must be in contact with other parts on a scale of time to coordinate the variations of luminosity. Thus a quasar whose luminosity varies on a scale of time of a few weeks can be larger only some week-light .
The quasars show many properties comparable with those of the active galaxies: the Rayonnement is not-thermics and some have jets and lobes as those of the Radiogalaxie S. the quasars can be observed on many areas of the electromagnetic Specter: the waves radio, Infra-red S, the visible Light, Ultraviolet S, the x-rays and even the gamma rays.
The majority of the quasars are most brilliant in the field of the ultraviolet close relation (~ 1216 Angström S, which corresponds to the emission line Lyman-α of the Hydrogène) in their clean Référentiel, but because of the considerable redshifts of these sources, the peak of luminosity was also observed far 9.000 has.
The quasars of iron show very strong emission lines resulting from ionized iron, such as WILL GO 18508-7815.
Generation of emission
As the quasars show properties common to all the active galaxies, much of scientists the emissions of the quasars compared and that of the small active galaxies due to their similarity. The best explanation for the quasars is than they become powerful thanks to the black holes supermassifs. To create a luminosity of 10 40 W (typical brightness of a quasar), a supermassif black hole should consume the equivalent matter of 10 per annum star S. The most brilliant quasars are known to devour 1.000 solar matter masses per annum. The quasars are known to ignite or die out according to their environment. One of the implications is that a quasar could not, for example, to continue to nourish itself at this rate/rhythm during 10 billion years. What explains rather well why there is no quasar close to us. In this case of figure, when a quasar finished to swallow gas and dust, it becomes an ordinary galaxy.
The quasars also provide indices as for the end of the Réionisation of the Big bang. The oldest quasars (Z > 4) show that a wave Gunn-Peterson and areas of absorption in front of them, indicating that the intergalactic Espace was made neutral gas, to this moment. More recent quasars show than they do not have any area of absorption but rather spectra containing a zone with a peak known under the name of Forêt Lyman-α. That indicates that intergalactic space underwent a reionisation in the plasma, and that the neutral gas exists only in the shape of small clouds.
Another interesting characteristic of the quasars is that they show traces of elements heavier than the Hélium. That indicates that these galaxies underwent an important phase of formation of stars creating a population III of star, between the time of the big bang and the observation of the first quasars. The light of these stars could be observed thanks to the Space telescope Spitzer of NASA (though fine 2005, this interpretation still requires to be confirmed).
The first quasars were discovered with Radiotélescope S, towards the end of the the Fifties. Many was recorded like radio sources without associated visible object. By using small telescopes and the Telescope Lovell like Interferometer, one noticed that they had very an angular small size. Hundreds of these subjects were indexed as of 1960 and indexed in the Third Cambridge Catalog. In 1960, the source radio 3C 48 was finally connected to an optical object. The astronomers detected what appeared to be a pale blue star at the place of the radios sources and obtained his spectrum. Containing unknown emission lines enormously - the irregular spectrum defied any interpretation -, the claim of John Bolton speaking about large a redshift was not accepted.
In 1962, an opening was accomplished. Another radio source, 3C 273, was going to undergo five Occultation S by the the Moon. The measurements taken by Cyril Hazard and John Bolton during one of screenings, by using the radio telescope of Parkes, made it possible Maarten Schmidt to identify the object from the optical point of view. It obtained an optical spectrum by using the Télescope Hauls (5,08 m) on the Palomar Mount. This spectrum revealed the same strange emission lines. Schimdt realized that they was the redshiftées lines of hydrogen (shifted towards the red) of 15,8%! This discovery showed that 3C 273 moved away at the speed of 47.000 km/s. This discovery revolutionized the observation of the quasars and allowed others Astronome S to find redshifts emanating of the emission lines and coming from other radio sources. As Bolton had predicted earlier, 3C 48 proved to have a redshift equivalent to 37% of the Speed of light.
The word “quasar” was invented by the Astrophysicien Chinese Hong-Yee Chiu in the review Physics Today , to describe these intrigants objects which became popular shortly after their discovery, but which was not indicated solely by their complete name (quasi-stellar radio cource):
For the moment, the rather awkward word and indéterminable of “quasi-stellar radio source” is used to describe these objects. As the nature of these objects is completely unknown for us, it is difficult to give them a short and suitable nomenclature, even if their essential properties come from their name. By practical spirit, the shortened form “quasar” will be used throughout this article. |Hong-Yee Chiu|Physics Today, May 1964
Later, it was discovered that all the quasars (in fact, only ~ 10%) did not have strong radio transmissions. From here name “QSO” ( quasi-stellar object ) is used (in addition to the word “quasar”) in reference to these objects, including/understanding the class of the radio-extremely and the radio-silencer .
The great subject of debate in the the Sixties was to know if the quasars were close or remote objects as them redshift supposes it. It was suggested, for example, that the redshift quasars was not with the Doppler effect, but rather with the light escaping from a deep gravitational well. However, a star with a sufficient mass to form such a well would be unstable. The quasars also show unusual spectral lines, which were visible before on a hot Nébuleuse basic density, which would be too diffuse to generate energy observed and to reach the deep gravitational well. It also had serious concern with regard to the idea of quasar cosmological distances. One of the main arguments in their discredit were that they implied energies which exceeded the known processes of conversion, including the nuclear Fusion. At this stage, some suggested that the quasars were made of a form of Antimatière stable unknown factor up to now and who could pass to be their brightness. This objection was erased with the proposal of a mechanism of Disque of accretion, in the Années 1970. And today, the cosmological distance from the quasars is accepted by the majority from the researchers.
In the Years 1980, unified models were developed in which the quasars were seen simply like a class of active galaxies, and a general consensus emerged: in much of case, it is only the visual angle which distinguishes them from the other classes, such as the Blazar S and the radiogalaxies. The immense luminosity of the quasars would be the result of a friction caused by gas and dust falling into the accretion disc from the black holes supermassifs, which can transform of about a 10% the Masse of an object into a energy comparable with 0,7% for p of the process of nuclear fusion and which dominates the energy production in stars like the Sun.
This mechanism also explains why the quasars were more common when the Universe was younger, like the fact why this energy production finishes when the supermassif black hole consumes all gases and all dust being close to him. That implies the possibility that majority of the galaxies, whose our Milky Way, passed by an active stage (seeming being quasars or another active class of galaxy depending on the mass of the black hole and of its accretion disc) and are now peaceful because they do not have any more what to be nourished (in the center of their black hole) to generate radiations.
Astrofiles: the quasars
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