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Author Topic: 50 Billion Suns! -The Biggest Single Object in the Universe !  (Read 40683 times)

Offline LeeE

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« Reply #25 on: 16/03/2009 14:30:34 »
Still the question remains; how can a black hole gain mass if nothing can get past the event horizon?

I still suspect there is something not yet discovered that prevents anything from reaching the singularity. It will always be approaching it; never reaching it; like repeated instances of getting half way there.

Actually, I'm very much inclined to agree with you.  The laws of Physics, as we currently understand them, just don't work beyond the event horizon because gravitational time-dilation means that the rate of time drops to zero at the event horizon, and you can't do physics without time.

The best answer I can come up with is that both space and time get 'stacked-up' and compressed around the event horizon, at a logarithmic rate, effectively allowing room for an infinite amount of space and time at the event horizon itself.  To a distant observer though, this all appears to occupy a finite volume of space, so although nothing can ever actually cross the event horizon and fall in to the singularity, the total amount of mass in the observed finite volume of space will have increased.
 

Offline DoctorBeaver

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« Reply #26 on: 16/03/2009 14:36:25 »
There are those infinities again!

Remember, time dilation does not affect the object falling into the black hole. In its own frame of reference it will still fall in at the rate expected. It is only to an outside observer that it will appear to fall slower & slower. That means that in the frame of reference of the falling object, the blackhole does gain mass.

I can't think past that stage at the moment  ??? but I'm sure it must have some relevance on the issue at hand. What's tickling my brain about it is the way time & space swap places inside, or at, the event horizon. Let me try to think it through & I'll see if I can come up with any of my normal nonsense.
« Last Edit: 16/03/2009 14:44:39 by DoctorBeaver »
 

Offline LeeE

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« Reply #27 on: 16/03/2009 14:58:28 »
There are those infinities again!

Remember, time dilation does not affect the object falling into the black hole. In its own frame of reference it will still fall in at the rate expected. It is only to an outside observer that it will appear to fall slower & slower. That means that in the frame of reference of the falling object, the blackhole does gain mass.

Yes, darn those infinities - I don't like 'em either, but I think you've got that a bit back-to-front.  To the observer, the object falling towards the black hole won't appear to move slower and slower, but accelerate, just as things appear to do when we drop something here on Earth.  Nothing that occurs outside of the event horizon is any different to what happens with non-black hole sized gravity wells; it's just a matter of degree.

If the observer is watching something time-based happen on the falling object though, it will appear as though that thing will be happening more slowly.  However, to the object itself, in it's local frame of reference, time will seem to be passing at the normal rate and it's everything else that seems to be changed.

The most important thing to remember is that the conditions for the observer do not change throughout this, but they do for the falling object.
 

Offline DoctorBeaver

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« Reply #28 on: 16/03/2009 15:44:46 »
Quote
If the observer is watching something time-based happen on the falling object though, it will appear as though that thing will be happening more slowly.  However, to the object itself, in it's local frame of reference, time will seem to be passing at the normal rate and it's everything else that seems to be changed.

That's what I meant. Maybe I phrased it badly.
 

Online yor_on

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« Reply #29 on: 17/03/2009 20:09:31 »
" A Lenticular Galaxy Reveals Spinning Black Holes "

And "The X-ray glow of those iron atoms is so intense that gravitational heating alone cannot explain it. What that unassuming little graph may represent is the detection of a new source of cosmic energy, one predicted a quarter century ago but never before observed"
Cool heh :)

http://discovermagazine.com/2008/whole-universe/09-a-lenticular-galaxy-reveals-spinning-black-holes
 

Offline Vern

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« Reply #30 on: 17/03/2009 20:36:23 »
Very interesting link yor_on; spinning black holes; I'm guessing that we will find that all black holes are spinning. If they are born of stars that are spinning, the angular momentum must be conserved. So the black hole would be a disk.
 

Offline dlorde

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« Reply #31 on: 17/03/2009 23:22:19 »
You're referring to what's known as "The Blue Curtain", where the time dilation is so great to an outside observer that it appears to stand still and matter seems to accumulate at the event horizon. Light accumulating in this way is infinitely blue-shifted (infinities again grrrrrr).
That's puzzling - when an object falls into a black hole, it's falling into an increasingly deep gravity well, effectively accelerating away from external observers - light escaping from the edge of the event-horizon should therefore surely be increasingly red-shifted. The photons emitted have the same energy, but it's spread out - stretched in space-time, so should become fainter and redder. By the time apparent movement stops, shouldn't the light be infinitely red-shifted as it takes infinitely long to climb out of the gravity well (although still at C) ??

Please resolve my conundrum.
 

Offline Vern

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« Reply #32 on: 17/03/2009 23:52:37 »
You may have an unresolvable conundrum. But you may have spotted a good measure of a black hole. It seems true that if we observe a black hole we should see red-shifted matter radiating back to us as it plummets inward toward the black hole. That should be a signature of a black hole.
 

Offline dlorde

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« Reply #33 on: 18/03/2009 00:16:59 »
Well whether the conundrum is unresolvable or not, surely someone can explain why the light is said to be blue-shifted, as if it somehow gains energy emerging from the gravity well, or as if the object falling in is accelerating towards us ???
 

Offline DoctorBeaver

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« Reply #34 on: 18/03/2009 00:22:38 »
It's not emerging, it's heading in. I'm not sure of the mechanics behind it, I just read about it. If I recall correctly it's more to do with time dilation.
 

Offline neilep

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« Reply #35 on: 18/03/2009 02:52:25 »
Does this mean that Disney's Black Hole is not authoritative ?
 

Offline Vern

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« Reply #36 on: 18/03/2009 04:13:35 »
Disney's black hole is good theatre. I suspect it represents very little similarity with reality. We are still guessing when it comes to the true nature of black holes.
 

Offline LeeE

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« Reply #37 on: 18/03/2009 08:11:53 »
Does this mean that Disney's Black Hole is not authoritative ?

Well, old Walt was always more of a biologist than a physicist.
 

Offline DoctorBeaver

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« Reply #38 on: 18/03/2009 10:23:39 »
Does this mean that Disney's Black Hole is not authoritative ?

Well, old Walt was always more of a biologist than a physicist.

But look what he did to Bambi's mum. Killed her, he did. Killed her stone dead! Poor Bambi.
 

Offline dlorde

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« Reply #39 on: 18/03/2009 12:10:06 »
It's not emerging, it's heading in. I'm not sure of the mechanics behind it, I just read about it. If I recall correctly it's more to do with time dilation.
The object is heading in, sure - but the light it emits must be heading out, otherwise we wouldn't see it. ISTM the time dilation that makes the inward fall and the timeframe of the object appear to slow, will surely increase the wavelength of the light it emits - and the same number of photons over a longer period at longer wavelengths will make it correspondingly dimmer...? [I'm considering this independently of the radiation emitted by the frictional heating by tidal forces of infalling matter from the accretion disk]

DoctorBeaver do you remember where you read about this? My curiosity is aroused now - I'm going to have to find out :-)
 
 

Offline dlorde

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« Reply #40 on: 18/03/2009 12:18:37 »
Aha, found it - on Wikipedia (Falling Into A Black Hole):
Quote
...From the viewpoint of a distant observer, an object falling into a black hole appears to slow down, approaching but never quite reaching the event horizon: and it appears to become redder and dimmer, because of the extreme gravitational red shift caused by the gravity of the black hole. Eventually, the falling object becomes so dim that it can no longer be seen, at a point just before it reaches the event horizon. All of this is a consequence of time dilation: the object's movement is one of the processes that appear to run slower and slower, and the time dilation effect is more significant than the acceleration due to gravity; the frequency of light from the object appears to decrease, making it look redder, because the light appears to complete fewer cycles per "tick" of the observer's clock; lower-frequency light has less energy and therefore appears dimmer, as well as redder.

 

Offline DoctorBeaver

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« Reply #41 on: 18/03/2009 21:48:02 »
I read it in a book by John Gribben, the author of many science books. I borrowed it from a library about 4 years ago.

Looking through his list of books I found "Unveiling the Edge of Time: Black Holes, White Holes, Worm Holes ". It could have been that 1.
 

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« Reply #42 on: 19/03/2009 00:59:02 »
DB, here is the link to that those 'new' BH I was referring too. As I read it over a year ago and also found that it then was quite supported by a lot of physicists, it made me wonder where it had gone. http://www.physorg.com/news101560368.html "what is controversial about the new finding is that "from an external viewer's point it takes an infinite amount of time to form an event horizon and that the clock for the objects falling into the black hole appears to slow down to zero," said Krauss, director of Case's Center for Education and Research in Cosmology."
« Last Edit: 19/03/2009 01:01:05 by yor_on »
 

Offline dlorde

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« Reply #43 on: 19/03/2009 00:59:41 »
I read it in a book by John Gribben, the author of many science books. I borrowed it from a library about 4 years ago.
Oh yes, Gribben - I've got some of his - 'In Search Of Schroedinger's Cat', 'Schroedinger's Kittens', 'the Matter Myth'. He's usually pretty good.
 

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« Reply #44 on: 19/03/2009 11:08:49 »
The evidence for Black Holes seems rather overwhelming :)
But when it comes to those spinning at almost 'c' I can't help wondering over how this framedragging expresses itself. First you have the sheer mass in itself, in a non rotating black hole (Schwarzschild geometry) you will have a point of no return at the EV. And with a spinning BH (Kerr metric)it seems to me that this 'point of no return' should be seen even further out, before reaching any EV (event horizon)? Shouldn't this move the EV? And also 'collect' the matter falling in into a concentrated 'density' dragging it around that BH as all matter has an 'inertia'?
« Last Edit: 19/03/2009 11:12:56 by yor_on »
 

Offline DoctorBeaver

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« Reply #45 on: 19/03/2009 11:16:36 »
I think I've remembered what that Blue Curtain thing is all about. It's from the perspective of an observer falling into the EH. Does that sound better?
 

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« Reply #46 on: 19/03/2009 11:50:31 »
If we have light emitted from a object falling into a spinning BH, that light will have to make its way back up the 'gravity well' to the observer, will it then do that 'both' ways, as seen thinking of that spin? I mean, being reflected going against that spin will give it a extreme redshift, but when reflected as light when 'spinning' towards you shouldn't it get a blueshift and because of that have a 'easier' way out from that BH, still being redshifted due to the gravity well but not as much as the light reflected seen from that other angle? But then again it will only have one way to go and that is searching the easiest path out, which will be a spiral, ah, forget it, the light can only go one way :)
And 'red blue shift' will be 'equalized' as it moves around I suppose?
Or, will it? Depending on where its finally comes from meeting your observer??
« Last Edit: 19/03/2009 11:54:10 by yor_on »
 

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Offline Vern

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« Reply #48 on: 19/03/2009 16:20:01 »
Quote from: yor_on
And 'red blue shift' will be 'equalized' as it moves around I suppose?
Or, will it? Depending on where its finally comes from meeting your observer??
It seems that a spinning black hole should appear as both red shifted and blue shifted depending upon the circumference observed. My guess is a galactic black hole would be spinning in the plane of galaxy in the centre of a huge accretion disk. I doubt that black holes exist as a singularity for the same reasons cited in yor_on's link. You can never get completely there because of the relativistic behaviour of light and matter.
 

Offline LeeE

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« Reply #49 on: 19/03/2009 18:18:29 »
I think I've remembered what that Blue Curtain thing is all about. It's from the perspective of an observer falling into the EH. Does that sound better?

That sounds reasonable.
 

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« Reply #49 on: 19/03/2009 18:18:29 »

 

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