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Author Topic: Should an event horizon actually stop light and why?  (Read 3151 times)

Offline jeffreyH

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If the escape velocity at the event horizon is exactly c then doesn't it follow that light having this exact velocity should still be able to escape? It it was c+n then that would exceed light speed. Can someone explain this?


 

Offline jeffreyH

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Re: Should an event horizon actually stop light and why?
« Reply #1 on: 12/02/2014 01:43:35 »
As an addendum, it could be the additional angular momentum at the equator of a spinning black hole that increases the escape velocity past light speed. At the poles of a black hole this would not be the case so any light that could escape would do so there. This would be a good explanation for relativistic jets. This then raises the question could the escape velocities differ at the poles and the equator due to density differences?
« Last Edit: 12/02/2014 01:45:25 by jeffreyH »
 

Offline jeffreyH

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Re: Should an event horizon actually stop light and why?
« Reply #2 on: 12/02/2014 01:51:34 »
This new research is very interesting on spin rates.

http://www.nature.com/news/spin-rate-of-black-holes-pinned-down-1.13512
 

Offline Ethos_

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Re: Should an event horizon actually stop light and why?
« Reply #3 on: 12/02/2014 02:23:43 »
If the escape velocity at the event horizon is exactly c then doesn't it follow that light having this exact velocity should still be able to escape? It it was c+n then that would exceed light speed. Can someone explain this?
Actually Jeff, when the escape velocity exceeds c, the black hole will form. As a consequence, the event horizon becomes the barrier beyond which light can not escape. What lead you to believe that the event horizon had an escape velocity of exactly c? Black holes have varying degrees of total mass some of which are millions of times the mass of our sun. In such supermassive black holes, the escape velocity would be many, many times the speed of light.
 

Offline jeffreyH

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Re: Should an event horizon actually stop light and why?
« Reply #4 on: 12/02/2014 11:57:34 »
Well doesn't that mean that light will be unable to escape from mass above a critical size before the collapse reaches the event horizon? In theory then some masses must be so big that light speed is reached without any collapse. In other words we should be able to calculate a critical mass with Ve = c when the mass is at what we consider a normal density.
So our mass will be calculated by M = c^2*r/2G. We can then calculate all mass sizes with Ve = c by varying r. This will of course not describe mass density without further calculation of volume. To find the critical mass we need to add this.
« Last Edit: 12/02/2014 12:10:58 by jeffreyH »
 

Offline jeffreyH

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Re: Should an event horizon actually stop light and why?
« Reply #5 on: 12/02/2014 12:14:39 »
I think the main problem here is that it is not well understood that the mass itself is affected by time dilation due to gravitational feedback. c should only be reached AT the event horizon. Einstein's sum of the form 1 + 1/2 + 1/4 + 1/8 + 1/16 .... means that the feedback affects dilation and contraction WITHIN the mass itself.
 

Offline JP

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Re: Should an event horizon actually stop light and why?
« Reply #6 on: 12/02/2014 12:22:20 »
Once light can't escape, gravity overcomes all forces that hold matter apart and keep it from collapsing (since they are, at the fastest, transmitted at light speed).  So going past that critical limit automatically implies collapse, unless some new physics comes in that we don't yet know about.
 

Offline jeffreyH

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Re: Should an event horizon actually stop light and why?
« Reply #7 on: 12/02/2014 12:54:53 »
Once light can't escape, gravity overcomes all forces that hold matter apart and keep it from collapsing (since they are, at the fastest, transmitted at light speed).  So going past that critical limit automatically implies collapse, unless some new physics comes in that we don't yet know about.

I agree with all the above. BTW I was dubious about singularities until I considered the idea of massless particles beyond the event horizon. How would the Higgs field behave in a black hole?
« Last Edit: 12/02/2014 12:58:10 by jeffreyH »
 

Offline jeffreyH

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Re: Should an event horizon actually stop light and why?
« Reply #8 on: 12/02/2014 13:42:52 »
If we now look at the Schwarzschild radius calculation rs=2Gm/c^2 this can then be rearranged as m = c^2*rs/2G. From above we have M = c^2*r/2G. The question is how does r vary with respect to rs? Do they converge at some point?
 

Offline jeffreyH

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Re: Should an event horizon actually stop light and why?
« Reply #9 on: 12/02/2014 14:03:36 »
The first graph shows uncompressed v Schwarzschild mass against radius for Ve = c. The second show only the Scwarzschild values. In the first graph the Schwarzschild values are almost coincident with the y axis. According to this, yes Ve can exceed c before an event horizon is reached but no account of gravitational feedback is taken into consideration.
« Last Edit: 12/02/2014 14:05:31 by jeffreyH »
 

Offline jeffreyH

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Re: Should an event horizon actually stop light and why?
« Reply #10 on: 12/02/2014 14:11:43 »
If we consider that time is dilated at the surface of a spherical mass then to an external observer the escape velocity does not appear to equal the value that the observer would calculate for the mass size under consideration. There is a deviation. If this value is calculated by an external observer viewing a black hole where Ve at the radius is exactly c he will not observe light and conclude that it cannot escape. Is this really the situation? For him light speed is invariant. The time dilation must also affect the rate at which photons can be emitted. It may be in some cases that those photons are emitted once every year or over more extended periods of time and at wavelengths that are undetectable.
« Last Edit: 12/02/2014 14:14:02 by jeffreyH »
 

Offline jeffreyH

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Re: Should an event horizon actually stop light and why?
« Reply #11 on: 12/02/2014 14:34:01 »
Actually the range r - rs should give us a mass density function that can be related to Ve. As only the density per unit volume changes. This density function can then be related to g at the surface. In the first graph the Ve at rs WILL exceed c.
« Last Edit: 12/02/2014 14:36:55 by jeffreyH »
 

Offline jeffreyH

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Re: Should an event horizon actually stop light and why?
« Reply #12 on: 12/02/2014 15:50:48 »
I was right I forgot to take the square root of the mass in graph 1. Here it is with both plots coincident. With c as a set escape velocity then varying only r as dr in the first equation has a direct proportionality between r and rs that is determined by the square root of the mass. They are not exactly coincident because of absolute values at the Planck scale.
« Last Edit: 12/02/2014 15:59:02 by jeffreyH »
 

Offline jeffreyH

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Re: Should an event horizon actually stop light and why?
« Reply #13 on: 12/02/2014 18:22:44 »
It seems that for smaller condensed objects Ve < c. I need to find out where the Chandrasenkhar limit falls on this plot. This indicates that a mass such as the sun would be just under the limit for compression into a black hole.
« Last Edit: 12/02/2014 18:26:35 by jeffreyH »
 

Offline evan_au

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Re: Should an event horizon actually stop light and why?
« Reply #14 on: 12/02/2014 20:07:56 »
The Chandrasekhar limit is not fundamental to mass and gravity, but is related to the pressure which can be sustained by electron degeneracy. When the pressure in the core of a white dwarf star rises above this limit, the star will collapse into a neutron star or black hole.

A similar limit applies to accreting neutron stars - once the pressure in the core exceeds the pressure which can be sustained by neutron degeneracy (or perhaps by a hypothetical quark-gluon soup), it will collapse to a black hole.
 

Offline jeffreyH

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Re: Should an event horizon actually stop light and why?
« Reply #15 on: 12/02/2014 22:50:47 »
The Chandrasekhar limit is not fundamental to mass and gravity, but is related to the pressure which can be sustained by electron degeneracy. When the pressure in the core of a white dwarf star rises above this limit, the star will collapse into a neutron star or black hole.

A similar limit applies to accreting neutron stars - once the pressure in the core exceeds the pressure which can be sustained by neutron degeneracy (or perhaps by a hypothetical quark-gluon soup), it will collapse to a black hole.

Thanks for the reply. The pressure and density relationship is something I am looking at. That clears up a lot of questions.
 

Offline jeffreyH

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Re: Should an event horizon actually stop light and why?
« Reply #16 on: 13/02/2014 00:57:30 »
Interestingly the Chanrasenkhar limit falls at around the knee of the curve on the graph of escape velocities v rs above. This is before the curve starts to flatten out as it approaches Ve = c. The pressure required for neutron star collapse has to be a function of a range of mass sizes around this bend in the curve. As this will be below Ve = c it would require a further catastrophic collapse beyond rs to produce a singularity.
 

Offline jeffreyH

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Re: Should an event horizon actually stop light and why?
« Reply #17 on: 13/02/2014 02:05:32 »
I need to put together a function for degeneracy pressure. I have the equation at Wolfram http://scienceworld.wolfram.com/physics/ElectronDegeneracyPressure.html but what is the ratio of electrons to protons?? Surely these would be equal or am I missing something? Is this referring to matter in exotic states? BTW a correction to the above post. I should have said white dwarf instead of neutron stars.
« Last Edit: 13/02/2014 02:09:00 by jeffreyH »
 

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Re: Should an event horizon actually stop light and why?
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