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: http://zebu.uoregon.edu/1996/ph123/qso.html
Дата изменения: Thu May 23 23:52:19 1996 Дата индексирования: Tue Oct 2 00:43:41 2012 Кодировка: Поисковые слова: lightning |
What Feeds The Monster?
The basic problem was that the emission lines were at wavelengths which were unfamiliar to astronomers. Either these were new atomic processes at work, or something very odd was going on.
After a few of these objects were discovered it was soon realized that the emission lines were from normal atomic processes (i.e. electronic transisitions in Hydrogen and Oxygen) but that the redshift of the "Quasi-stellar" objects was enormous.
Implications of the large redshifts:
Further observations of QSOs showed the following set of characteristics as well:
We now have a fairly major problem: --> What physical process can
output so much energy in such a small volume?
Energy Requirements:
1 Lsun = 4 x 1033 ergs per second
For a 1 Msun star, E=mc2 gives the following energy:
which is then
The requirement is 4 x 1046 ergs per second and since there
are 3 x 107 seconds in a year this is then 1.2 x 1053
ergs per year.
Hence if we could convert 1 solar mass per year into energy with 10%
efficiency we could reach the observed luminosities of QSOs.
Observed luminosity is about 100 times that of the
Milky Way Galaxy. The luminosity of the Milky way is
There is only one possibility:
Gravitational Infall of matter onto a very large black hole. In this case the mass of the black hole needs to be about 108 Msun. A black hole this large has a radius of about 10 Astronomical Units (or about the distance between the Sun and Saturn).
A region this small is consistent with the short time scale variablity of emission that we measure.
So, are QSOs then naked -- that is, do we have these 108 Msun black holes roaming around the Universe looking for stars to eat? What is the mechanism that feeds these objects? If they are not fed matter, they do not produce luminosity on their own.
In the mid-80's it was determined from CCD imaging of some low redshift QSOs that the QSOs were located in the centers of galaxies and hence are just a more luminous form of Active Galactic Nuclei like Seyfert Galaxies . So if QSOs are hosted by galaxies then the only remaining challenge is to feed them.
Since QSOs are far more common when the Universe was young then the feeding mechanism must be fostered by conditions which were present then compared to now.
Many nearby QSOs show evidence of interacting with another galaxy. Galaxy-galaxy interactions are a good way of funnelling material down to the nucleus of a galaxy and if a monster is there, voila a QSO is produced. In general it is the transfer of gas onto a galactic nucleus that hosts a "monster" which activates the QSO. Interactions between gas-rich galaxies were far more common in the early Universe than now. This explains why most QSOs were borne a long time ago and have died out by now.
A lot of times the nuclear region will be very dusty and most of the emission produced comes out in the infrared. Very infrared luminuous objects known as Ultraluminous IRAS galaxies have been detected and are thought to be like QSOs. All of thse Ultraluminous IRAS galaxies are merging galaxies where gas is being forced down into the nucleus.
If this sceneraio is correct, then there should be nearby examples of dead QSOS --> that is galaxies with big massive black holes in them and the QSOs mechanism is no longer active. At the moment, only this galaxy (M87) seems to have one of these dead monsters in it.
Final note: the proliferation of QSOs in the early Universe and their associated intense UV radiation becomes a significant source of ionizing radiation which could help to delay the formation of galaxies until later times.
More about Quasars: