Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: litespeed on 03/11/2009 19:13:01
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Isn't a quasar simply a Black Hole that has lots of food? If so, this seems to imply they are defined by an arbitrary specification of ACTIVITY, not kind. To me, this seems to imply they were much more likely to form and accumulate their vast feast when the Universe was much more tightly packed.
In otherwards, they were created and prowled about the early universe through simple expedient of available food. This seems to me a self limiting motive operandi. As the Universe becomes less dense, there is less and less likelyhood one could find enough stuff to produce the phenomena we call Quasi Stellar Radio Objects
Mod edit - formatted the subject as a question - please do this to help keep the forum tidy and easy to navigate - thanks.
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Members of the forum here seem to think so. And it seems that many assume that a Quasar happens at the beginning of galactic birth. I view them more as a light source for viewing the early universe. We can glean lots of stuff from their spectra.
Stuff like 28 billion years ago second generation stars existed. That kinda puts a kink in our speculation about a 13 billion year old universe. [:)]
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It does seem fair to assume that once all of the quasar's available 'food' has been consumed it'll start going hungry and quieten down.
I'm not so sure it would come down to the universe being more tightly packed though. As quasars are a local effect, albeit on a galactic scale i.e. a quasar in one galaxy can't consume material in another, as soon as the galaxies have separated, the density of the universe i.e. how tightly packed the galaxies are, shouldn't be an issue.
A possible model of quasar formation (that I've just made up) is that they occur when spiral galaxies form around a pre-existing black hole. The dispersed pre-glalactic matter surrounding the BH falls towards it, and as the particles within this matter will have some initial velocities, they will mostly fall in on elliptical paths. Through collisions, some of the matter will end up in relatively stable orbits around the BH, and some of the matter will ejected with enough velocity to escape the proto-galaxy after a close encounter with the BH, but a large amount will end up being consumed by the BH, releasing the energy we see.
Although the direction from which the in-falling matter comes will be random, overall there will be a net direction to the in-fall. Similarly, the in-falling matter will have random charge, but which will once again result in an overall net charge. The result of these two factors is that the energy released by the in-falling matter will will tend to have an axis along which it flows and this energy flowing out of the 'poles' (defined by the axis) will tend to blow away or slow in-falling matter. Either way, it leads to a 'clearing' of the regions above and below the poles, with the slowed matter that is not blown away falling out of orbit and being consumed.
During the early stages of formation of the galaxy, when relatively little material has fallen into the BH, the axis will be correspondingly ill-defined and the energy released will be equally unfocused; the 'jets' it produces will be very broad, leaving only a thin, almost planar, region between the two lobes of the jets where material in stable orbits might be little affected.
As the galaxy and its central BH continue grow, as matter continues to fall into it, their rotation and charge becomes more clearly defined, as do the quasar's 'jets'. Eventually though, all that's left of the original pre-galactic matter is the stuff left in stable orbit around the BH, with the matter that was above and below the galaxy having been either consumed or blown away. In the end, what's left in the galaxy is in stable orbit and the quasar runs out of 'food'.
Please remember that I have only just literally made this up, but it occurred to me as a possible reason why it might not be as simple as just being a BH with a lot of food, or more correctly, why a BH might only be able to get enough food when the universe was much younger than it is now i.e. before most of the galaxies had fully formed.
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Lee - You wrote: "...a quasar in one galaxy can't consume material in another, as soon as the galaxies have separated, the density of the universe i.e. how tightly packed the galaxies are, shouldn't be an issue."
I have heard evidence Quasars can actually be created when Galaxies colide. Further, one common understanding of galaxy formation is they grew larger and larger with more and more structure as the accumulated or otherwise merged together over long periods of time.
Theoretically, all the earlier tumult would offer much higher odds for hungry Quasars in a target rich environment. This would explain why most if not all Quasars are very very old. They simply vacuumed up much of the early universe near them and so don't seem to be forming as much in later eons.
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Of course it is.
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I have heard evidence Quasars can actually be created when Galaxies colide.
But if two (or more) galaxies are colliding then they aren't separated are they? It sounds quite plausible though. If a quasar quietens down once the remaining matter in its host galaxy is in stable orbit around the central BH, creating in effect, a central void around the the BH, it seems quite possible that the quasar will reawaken if a colliding galaxy results in material falling in to the void where it can then be consumed.
Further, one common understanding of galaxy formation is they grew larger and larger with more and more structure as the accumulated or otherwise merged together over long periods of time.
I don't see any contradiction here, except that collisions tend to make the structure less organised rather than more organised. The pre-galactic material that eventually coalesces in to a galaxy must have occupied a greater volume than the resultant galaxy and as all of the material couldn't have aggregated instantly, it must have been a progressive process. Hence the galaxies would have been more tenuous and ill-defined in their earlier stages than in their later ones. The many irregular galaxies we see, which also tend to be pretty small, may be galaxies where there was just insufficient pre-galactic material to become well-formed.
Interestingly, the largest elliptical galaxies, which are believed to have grown as a result of collisions and mergers have very little, or in some cases, no structure.
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Lee
Yeah, elliptical galazies have me stumped, thats for sure. I have not read up on them but they seem to suggest a few questions to start with. First, the stars in such galaxies must be orbiting something, otherwise they would collapse into an acreation disc of some sort. Second, are they all orbiting in some sort of ramdom manner about the center mass, thus keeping them from forming an acretion disc.
Finally, perhaps they actually ARE in the process of eventually forming an accretion disc and spiral galaxy, but the accumulated orbits are sufficiently distributed to make this a slow process.
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Finally, perhaps they actually ARE in the process of eventually forming an accretion disc and spiral galaxy, but the accumulated orbits are sufficiently distributed to make this a slow process.
The only problem with that litespeed, is that ellipticals are generally much bigger than spirals, so you'd need some sort of mechanism for the elliptical to lose a lot of mass as it develops from an elliptical into a spiral.
Having said that though, the scenario is similar in some ways to the one I hypothesised earlier, at least with regard to the random orientations of the orbiting stars. The important difference is that ellipticals seem to have very little interstellar material, so any central BH, which would represent a very small target, would have to rely upon direct hits from orbiting stars, whereas the BH in a developing spiral in that hypothetical model could feed continuously upon large expanses of pre-stellar matter.
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The generally accepted model for galaxy evolution is that spiral galaxies form large ellipticals by colliding and going into orbit around each other this eventually destroys the disc structure to form an amorphous blob full of streams of stars that are the relics of the smaller galaxies that have combined. many large elliptical galaxies have a very great number of globular clusters these are probably the inner cores of the smaller galaxies which because of their stabilising black holes have resisted disruption by the gravitational gradients that they have encountered
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I doubt that globular clusters are the nuclei of smaller galaxies that have been absorbed by the parent galaxy, and I doubt that they contain super-massive, or even massive, black holes.
Our fairly well formed spiral galaxy has 158 known globular clusters, and it's thought that there are probably another 10-20 that we can't see directly. If our galaxy had experienced that many collisions then it probably would not have such a simple structure and it would be more chaotic. Having said that, I do believe that our galaxy is in the process of absorbing a small irregular/dwarf galaxy atm. However, small irregular galaxies and most dwarfs don't seem to have central black holes - these types of galaxy are generally pretty tenuous and insubstantial.
Edited to include the missing 'not' - Oops!
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Globular clusters need a high mass concentration at their centre to stabilise them this probably includes one or more stellar mass black holes
Many Globular clusters are probably the relics of the earliest "stars" (some of which may have collapsed straight to form 100 solar mass black holes). They formed small compact "galaxies" because when the big central star or group of stars exploded before the rest of the material had collapsed on to them and the expanding turbulent shock wave triggered star formation. they orbit larger galaxies in all direction s and often pass through the disc but they are stable enough to resist rapid disruption.
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I wouldn't dispute the presence of super-solar sized black holes in the globular clusters any more than I'd dispute them being scattered through the Galaxy in general; if there are stars there will be black holes, but even a 100 solar mass BH isn't massive, let alone super-massive.
However, globular clusters do not need a high mass concentration at their center, at least in terms of a very large single body; all of the individual stars only need be orbiting their common barycenter. The barycenter of each individual star will be based upon its personal location and the average position of all the other stars, which will be at the center of the cluster. The effect will be of each individual star orbiting a single virtual body located at the center, even though that single body doesn't actually exist.
Certainly, small compact galaxies exist, and being made of stars, they'll contain black holes, but compared with the Galaxy, both small compact galaxies and globular clusters are tiny, and seem to lack sufficient material to form massive black holes.