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Mantis von Presley
2010-Apr-23, 06:00 PM
Hello all,

I have been reading up on quasars and I wanted to double check that my understanding of them was correct. After researching this phenomena I am left believing that quasars are not actually a thing in and of themselves, but the "visable" effect of a black hole's accretion of matter. Am I correct in this? I would appreciate any help I could get in the matter. Thank you.

Jeff Root
2010-Apr-23, 06:54 PM
Your understanding is correct. A quasar, as best we can tell, is what is
seen when matter gets very close to a supermassive black hole and is
accelerated to extreme speeds, giving off lots of light over a very wide
range of frequencies.

-- Jeff, in Minneapolis

Spaceman Spiff
2010-Apr-28, 07:04 PM
Hello all,

I have been reading up on quasars and I wanted to double check that my understanding of them was correct. After researching this phenomena I am left believing that quasars are not actually a thing in and of themselves, but the "visable" effect of a black hole's accretion of matter. Am I correct in this? I would appreciate any help I could get in the matter. Thank you.

(snip)
the "visable" effect of a black hole's accretion of matter can also be said of a star: they are the visible effect of an enormously massive, self-gravitating ball of gas in dynamical equilibrium. The rest just pops out from there. Are stars things?

Or another way of looking at it: the gist of the above quote can be said of "every"thing, because, as far as science's study of nature is concerned, there is "no"thing. Even without opening the can of worms that all that we know from science is only a model of "what is", an electron is a not a thing and neither is a quark. If you feel the need to consider them as "things", then you'll need to re-calibrate your definition. Science addresses phenomena. Quasars are a phenomenon, or rather a collection of nested phenomena. And so are you.

Van Rijn
2010-Apr-29, 01:16 AM
What's interesting to me is that it's only fairly recently that we've had a decent idea of what quasars are. In my university days, "quasistellar objects" were still a big mystery. There were a number of ideas of what they might be, but there was no clear winning theory at that time. It took more observation and more theoretical work for it all to come together.

Spaceman Spiff
2010-Apr-29, 12:49 PM
What's interesting to me is that it's only fairly recently that we've had a decent idea of what quasars are. In my university days, "quasisteller objects" were still a big mystery. There were a number of ideas of what they might be, but there was no clear winning theory at that time. It took more observation and more theoretical work for it all to come together.

That has been my experience, as well. The introduction of photometric spectroscopy and imaging, with efficient detectors on large ground-based telescopes and the IUE ultraviolet satellite in space, got the ball rolling. Looking backward, one can see the slow, grinding progress of science.

Jeff Root
2010-Apr-29, 03:23 PM
My own hypothesis was that they were the cores of young galaxies
with supernovae of first-generation stars occuring as frequently as
several per day.

-- Jeff, in Minneapolis

fwsocial
2010-May-05, 11:45 PM
Nope Jeff, supernovas are far too low in luminosity. The common understanding is that the radiation comes from a rotating accretion disk around the black hole. What happens is that the disk has internal friction due to differential rotation, and that friction is converted into heat radiated by the disk. The same friction causes the matter to lose mechanical energy so it is transported inward whereas angular momentum is transported outward. The liberated gravitational energy is E=GmM/R and inserting the black hole radius R=2GM/c*2 gives E=mc^2/2 but in reality E = 0.1mc^2. Nuclear fusion has E=0.007mc^2 so the process is extremely efficient thus explaining the quasar luminosity.