Thank you Amrit

As you can see from my naive question I am an engineer and not a physicist. Nevertheless, I was curious so thank you for your answer.  

What would be the correct term? is it "quasi-static"?. 

I was also expecting some comment on my use of the term "size".  

Michael, the Schwarzschild metric for a radially moving ingoing photon simplifies to dr/dt=2m/r-1 (the speed of light has been set to one and the photon's speed is negative here). Notice that the speed vanishes as the event horizon at r=2m is approached. We need only consider the range r>2m. This simple differential equation is not hard to integrate and shows that the time interval needed for the radial location of the photon to decline from r0 to r1 is:

Delta t = r1-r0 - 2m*ln((r0-2m)/(r1-2m))

Choose r0>>2m and r1=2m(1+epsilon) where epsilon

Mike, I am so glad this question isn't work related!

It so happens that this year's Reith Lectures on BBC Rdio 4 are by Stephen Hawking, on black holes.  There are two, at about half hour each, and they can be listened to or downloaded from:

http://www.bbc.co.uk/programmes/b00729d9/episodes/player

Well worth while!

John

“….what is a black hole? It is an object that doesn't allow light to totally escape…”

Thierry,

That isn’t correct, of course. The “black hole” in the GR  isn’t “an object that doesn't allow light to totally escape”, that is just a “hole” in the Matter’s spacetime.

Though what is a " hole in the spacetime"? – to claim that is evidently necessary, of course, previously to define – what are “space”, “time” and “spacetime”; when in the relativity theories there is no concrete definitions. When in some theory some parameter isn’t defined, then in such a theory  any, including absurd, consequences are possible. Including in the GR the “spacetime curvature” is postulated, that transforms in some cases, as a “ spacetime singularity”, into a “spacetime hole”.

In the Newton gravity a “black hole”  just as  “an object that doesn't allow light to totally escape” because of its large mass and comparatively small radius indeed is possible; and here is nothing strange, material objects aren’t  “spacetime”;  – but the radius in this case is twice lesser the Schwarzschild’s radius.

Cheers

Thierry,

“…Sergey: please don't associate GR with what happens in reality…”

-?

– I don’t…

Cheers

If we are to believe the theories of the day the size of the black hole that started it all would have been Infinite.  So If you believe the theory today there is no size limit.

Dear George

What do you mean by "the black hole that started it all"?

Mike

If there were and I say this lightly a start to the universe, as is dictated by the old theory of the big bang, there would have been a singularity which would have started as a collapse of a region of space that would be called a black hole.  This is by definition what a black hole is and would have been the start to the big bang theory.

Actually there is a practical upper limit on black hole mass and this may be a cause of why QSOs become extinguished.

At mass of about 2 x 10^9 solar masses, the tidal radius of a BH is now inside the event horizon and so objects cross the event horizon as a whole and are not tidally disrupted and heated to emit X-day.

Mass density largely determines tidal forces and for a black hole the density goes as M/R^3 = M/M^3 = 1/M^2

I have not heard this idea before. How would a lack of tidal heating in the infalling matter inhibit black hole growth? Also, are there no quiescent galactic nuclei whose black holes are not considerably lighter than 2 billion solar masses?

This has been known for quite some time

a reasonable paper (old) on this is 

http://adsabs.harvard.edu/full/1993ApJ...402...76B

the lack of tidal heating does not inhibit growth - in fact it probably enhances growth because there is no longer a strong radiation field around the event horizon - things simply fall in as a whole and are tidally disrupted inside the event horizon and so that radiation doesn't reach the external obsever

quasars can also be quenched simply by running out of material in their immediate environment to consume

Michael William Spindler · 20.76 · 15.77 · Électricité de France (EDF)

Dear George

What do you mean by "the black hole that started it all"?

Mike

Is there a maximum limit to the size of a black hole? - ResearchGate. Available from: https://www.researchgate.net/post/Is_there_a_maximum_limit_to_the_size_of_a_black_hole [accessed Feb 3, 2016].

Ответ.

Уважаемый Michael William Spindler 

Этот вопрос мной исследован в работах   Бураго С.Г. "The Black holes in the universe, filled by the gaseous dark matter" - See more at: http://gsjournal.net/Science- 

Journals/Essays/View/5909#sthash.1aq7NSPu.dpuf. February 2, 2015  

and 

 Article: The Black holes in the universe, filled by the gaseous dark matter 

 Sergey Burago · Researchgate.net

 Article: Черные дыры во Вселенной, заполненной темной газообразной материей  Sergey Burago ·Researchgate.net

мной была получена формула для радиуса "черных дыр"

r2=fxmo/axC,

где f=6,7x10-11Nm2/kg2-постоянная тяготения, mo-масса звезды или галактики, a=1c-1, C=3x108m/c-cкорость света.  

С уважением, Сергей Г. Бураго

I would say the Schwarzschild radius is good approximation for that.

 Thanks Dr Bothun

G. Bothun · 73.09 · 908.54 · University of Oregon

Actually there is a practical upper limit on black hole mass and this may be a cause of why QSOs become extinguished.

At mass of about 2 x 10^9 solar masses,

What becomes of the singularity at this mass?  Does it loose mass?  

The definition of a black hole and there are many, is a region of space where the mass of that region shrinks to below the Schwarzschild radius and from that point it becomes a black hole as no matter not even light can escape the gravitational field.  The event horizon of this void in space is the Schwarzchild radius. 

The idea that the start of the universe was from a singularity or a point of supper high density means that this region of space would necessarily have to be below the Schwarzchild radius and there for be a black hole by definition.  

If there is a maximum limit to the size of a black hole then this would imply that the big bang is false.  I know that the big bang did not happen but I am not willing to give up on the idea that black holes have not size limit if they exist.  We are still exploring the size of the black hole at the center of most spiral galaxies and they seem to suggest that there are some limiting factors to the size or some limiting rotational velocities that make it getting bigger a problem.  This is however subject to the Quantum uncertainty of the formation of systems like galaxies.   So there may be regions of space that have a high density but a slow enough rotation not to form a galaxy.  This is part of the cosmic microwave background anomaly information.  The cosmic background data shows very slight variations in the back ground and this could be caused by these regions of space that are not emitting light.

There is much more to this than can be discussed in just a few words in this blog.

If we look at the data that we are very sure of its validity and the basic understanding of physics we can come up with a much better understanding of why the Galaxies and the Universe look the way we see them.  This new look has little to do with a "big bang" and more to do with solving the problems that arise from a model of the Universe that is based on breaking the basic laws of Physics to start.

George   

In my opinion a black hole can be formed but the idea of its almost inevitable rotation with respect to matter falling in to the center of it is the part that we overlook.  This in my opinion is what causes the formation of galaxies and it has everything to do with the amount of matter that falls in and the rotation that is increased as a region collapses.  The size and shape of the galaxy is part of this dynamic.  There would be a correlation between the size that causes a collapse and the rotation that creates a spiral galaxy.  From this look into the sky at what is the most dominate form of galaxy it is the spiral.

The old model is not only wrong but leading us to bad new theories. 

G. Bothun, thanks for the clarification and the link to your paper. So you're not arguing that black holes are incapable of feeding above some threshold in mass, only that their feeding might not be so apparent observationally? My understanding is that galaxy clusters are still very rich in gas and that the supermassive black holes there should not be too starved of matter. This leaves me wondering why so few active galaxies are observed within low redshift clusters. Surely, the black holes have not already evaporated. Is it your contention that this is down to gentle accretion with relatively little tidal heating?

There appears to be an upper limit to how big the universe’s most massive black holes can get, according to new research led by a Yale University astrophysicist.

Natarajan found that ultra-massive black holes, which lurk in the centers of huge galaxy clusters like the one above, seem to have an upper mass limit of 10 billion times that of the Sun

http://news.yale.edu/2008/09/04/yale-astronomer-discovers-upper-mass-limit-black-holes

well if clusters have very big black holes in them, then they will not be active.

Our (observable?) Universe is a BH according to Schwarzschild radius' equation. This shows that there is no a BH radius' upper limit and I should argue that Universe as - a whole - is a BH is not just another coincident but a strong evidence we should use for our theories of cosmology.