The latest Nature Science update has a load of interesting stuff. Here's the first one, new quasars and galaxies at the edge of the observable universe.

http://www.nature.com/nsu/030106/030106-15.html

(It may require registration. I'm not sure about it though. Somebody let me know.)

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...And that, my liege, is how we know the Earth to be banana-shaped. --Sir Bedevere

No registration required. Horrible BA that they call quasars "enormous". They are smaller than our orbit around the sun as an upper limit, and more likely star sized. We know this from their variability.

They mean enormous in mass, not in radial size.

Don

No!

In the present quasar paradigm supported by observations, the supermassive black hole has a size equivalent to its Schwarzschild radius (which can be spherical, if not rotating, or flattened in shape if it is rotating, but nevermind), and this is:

R_sch = 3 km M/Msun

And if M = 1 billion solar masses (it ranges from a few hundred million to several billion in quasars), then just the Schwarzschild radius is 3 billion km. This takes you to 20 AU or nearly the orbit of Uranus. Now the continuous emission of light that spans from the infrared, optical, ultraviolet, and X-rays is emitted by gas in the vicinity of and in the process of being accreted by the black hole. The minimum stable orbit is something like ~3 R_sch, and so then we're talking about 60 AU in radius. X-rays generally show the strongest and most rapid variability and so is likely emitted by gas nearest the black hole. However, the restframe UV light that makes quasars so bright at optical wavelengths (due to their redshifts) is emitted by gas at a few 10s of R_sch, and in that case we are speaking of a few hundred AU -- corresponding to out into and beyond the Kuiper belt in size. These size scales are predicted theoretically and consistent with variability studies.

Some quasars were reported to vary on the scale a few minutes to 10s of seconds, strongly implying they are no larger than a few light minutes, or 10s of lightseconds, at the very upper bound and probably were much smaller. The black hole model is just a theory, but the observations are more consistent with being no larger than our orbit which is about 18 light minutes in diameter. It is more probable that they are much smaller. I was pushing your buttons with the age estimate, but a few 100 million yrs life doesn't seem to be consistent with the population for the non-intrinsic red shift model. A question which was: "How much equivalent mass is radiated away from the black hole by a typical quasar over its lifetime? Is this reasonable?" was answered by you on the other thread as
"Over a 100 million years the total energy radiated is something like 10^63 ergs at a luminosity near 10^47 ergs/s. That corresponds to ~1 trillion suns emitting a solar luminosity over 10 billion years. The total mass accreted corresponds to a whopping 0.1% or less of the total luminous mass of a massive galaxy. Big deal."
A trillion suns is for 10 billion years is about a 100 galaxies, assuming 10 billion suns per galaxy. I think you meant the mass radiated away, not accreted?? The accreted mass must be much greater, since the radiation is just a by product of the accretion process. Yep, a big deal. A big deal indeed. Not reasonable.


I, of course don't hold the black hole theory for quasars, but rather that they are nearby, intrinsically red shifted, and intrinsically rather dim.





<font size=-1>[ This Message was edited by: John Kierein on 2003-01-14 15:54 ]</font>

And your reference is? First, let me be clear that this is my field of professional research, and I am familiar with the literature. Second, more than likely you are confusing the observed X-ray variability time scales found in the low redshift, lower luminosity cousins of quasars called Seyfert 1 (Sy1) galaxies. We are actually measuring the masses of their (Sy1 nuclei) supermassive black holes via the observed motions and distances of the gas that emits the prominent broad emission lines – and they’re much less massive (as expected). Instead of billions of solar masses, they are 10s of millions of solar masses. Lower mass black holes are smaller, and X-ray emitting gas in their vicinities may vary on much shorter time scales. Let’s do the math again.

The last stable orbit is about

3 R_sch = 9 km * (M_bh/M_sun).

This is about 900 light seconds (or 15 light minutes) for a 30 million solar mass black hole. There are no observations (variability or other kind) that currently stand against the supermassive black hole paradigm of active galactic nuclei/quasars.

And why is that? What is your evidence? What's your argument based upon physical laws? There are currently no inconsistencies that arise from the data.

Ok JK, let’s do the math again.

L = 0.1 x mdot x c^2, where mdot is the mass accretion rate onto the black hole (in gm/s), c is the speed of light in a vacuum, and 0.1 is the mass-energy conversion efficiency for supermassive black holes (or conversion of gravitational potential energy into light energy). If L is 10^47 ergs/s, as is typical of luminous high redshift quasars, then mdot has to be about 18 solar masses per year. The mass converted to (light) energy is 10% of that, just as the expression says. In 100 million years, 1.8 billion solar masses of material will have been accreted onto the blackhole, 10% of which would have been converted into light (assuming constant mass accretion rate and luminosity). 1.8 billion solar masses is 1% the luminous mass of a moderate sized galaxy, but only 0.1% of such for very massive galaxies. As I said: big deal.

When I compared the luminosity of a quasar to that of a star like our Sun, it does not mean that the quasar has converted a trillion suns of mass completely into energy. You simply didn’t do the math right. I just told you that only 1.8 billion solar masses are required to be accreted by the black hole radiating at 10^47 ergs/s over a total of 100 million years, only 10% of which goes into the luminous energy. A luminosity of 10^47 ergs/s corresponds to 26 trillion solar luminosities. Yes, that’s right. In 100 million years this corresponds to about 3 x 10^62 ergs of light energy.

E = L * dt = 10^47 ergs/s * 10^8 yr * 3 x 10^7 s/yr = 3 x 10^62 ergs.

= m * c^2

= 0.1 * mdot * dt = 0.1 * 18 solar masses/yr * 2 x 10^33 g/solar mass * 10^8 yr * c^2

= 3 x 10^62 ergs, as above.

So I'll repeat again. A supermassive black hole (~ billion solar masses or so) will generate 10^47 erg/s of luminosity for 100 million years simply by dumping about 1.8 billion solar masses down into it. This means of course, that over the quasar's lifetime, its black hole will grow in mass - and so evolve in its luminous properties as well. Of course, too, the mass accretion rate is unlikely to be constant over the full life time.



<font size=-1>[ This Message was edited by: Spaceman Spiff on 2003-01-14 22:14 ]</font>

<font size=-1>[ This Message was edited by: Spaceman Spiff on 2003-01-14 22:15 ]</font>

Way to stand up for reason Spaceman Spiff. Indeed these quasars are huge objects (in mass) and the models do work very well for accretion onto a black hole in a dense, active galactic core. One can read about the efficiency of these processes in any number of papers on the subject (it's a very hot topic now). You can get efficiencies upwards of 10%mc^2 which is really quite remarkable and the masses needed for the luminosity are NOT a big deal at all.