Quasar
A quasar is the core of an active galaxy, which appears nearly point- shaped ( like a star ) in the visible region of light and emits very large amounts of energy in other wavelength regions. The name derives from Quasar English quasi -stellar object (, quasistellares object ') or quasi -stellar radio source (, quasi-stellar radio source ' ) from.
Discovery and naming
Historically, the term referred to cosmic radio sources, which were in the 1950s not be identified as radio galaxies, but blue in optical observations and " star-shaped " (ie not flat ) published. In 1963 Maarten Schmidt found that the radio source 3C 273 is not a nearby star, but with a redshift of 0.158 in the range further from galaxies, that is only quasi asteroid. Later observations showed that the bright star-like quasars are still embedded in the cores of galaxies, but appear weak because of the distance. The strong red shift due to the expansion of the universe quasars have been identified as very distant objects. This conclusion was independently confirmed since the discovery of gravitational lenses. Quasars have now been detected up to a redshift of 7.1.
With the made in 2010 discovery that the 1.6 billion light-years distant quasar SDSS J0013 1523 acts behind as a gravitational lens for a 5.9 billion light years distant galaxy, there is a direct way for determining the mass of a quasar.
The term quasi- stellar object QSO includes not only the classical radio-loud quasars, but also radio- quiet objects with weak radio emission, but otherwise similar characteristics. But the term quasar is often used somewhat inaccurate for both classes.
Physical Properties
Since quasars appear relatively bright in spite of their great distance, they are among the most luminous objects in the universe. Only very briefly glowing bright phenomena ( supernova, gamma-ray burst ) may be energetic. Quasars are bright over a wide range of electromagnetic radiation and have characteristic spectra with very broad emission lines which indicate befindliches moving swiftly gas.
Quasars are like the weaker Seyfert galaxies to the class of active galaxies. The separation based on the luminosity is purely historical. After today's adoption is in the center of all galaxies with a bulge a very massive black hole, which may include several millions to billions of solar masses. Active galaxies differ from normal galaxies by the fact that this black hole increases with time to ground, as matter from the surrounding galaxy ( interstellar gas, or torn stars) is attracted by the gravity of the black hole. This process of accretion of matter is called in astronomy accretion. Due to conservation of angular momentum in the infalling matter, it can not fall directly into the black hole, so as to form an accretion disk around it. By friction, this disc heats up, while at the same parts of matter lose angular momentum and so can fall into the black hole. The emission of the heated accretion disk is what is observed as typical radiation of the quasar. They may be similar to achieve a luminosity of many billions of stars and thus emit more light than the entire surrounding host galaxy. The most luminous quasars reach over 1014 solar luminosities.
If the accretion disk has a strong magnetic field, a small proportion of the matter stream is split in two, and forced into paths along the field lines of the magnetic field. Subsequently, both currents are perpendicular to the accretion disk plane ( one on each side ) repelled with relativistic speed in the surrounding galaxy and the other space. These so-called jets can then be observed in the radio wavelength range. A distinction is made in this context quasars in "radio loud " and "radio quiet" classes, according to the strength of the radio emission. However, it has been found that there is probably no real classes, but a continuous transition within the radio properties.
Blazar
The type of the optically violent variable quasar / OVV quasar, quasars with particularly rapid and strong variations in brightness, is expected along with the BL Lac objects, very bright, star seemingly similar objects, which consist of a very massive black hole at the crash brought matter polarized radiation with high brightness variation emitted to the group of so-called blazars. With them, one starts from an angle between the observation direction and the jet axis by a few degrees at most. Relativistic effects, tapering almost the speed of light to us jets can be "seen" in the highest-energy regions of the spectrum for these objects. The extremely rapid outflow of matter jets occurs in the core area of some quasars to a negative pressure, called relativistic inversion. The irregular accrete new material increases the variability. With the experiments EGRET ( GeV range ) and COMPTEL ( MeV range ) on the Compton Gamma Ray Observatory ten were found that glow in two regions of the spectrum. A similar link between quasars and blazars as is suspected between quasars and radio galaxies, where the jet axis is nearly perpendicular to the observation axis. These relationships are examples of " unified " models, in which different types of active galactic nuclei are explained by different observation directions to similar objects.