<p>With respect to "eternally collapsing", they are probably referrring to the fact that in the reference frame of an external observer, gravitational time dilation prohibits matter from ever reaching the event horizon (the "surface") of the black hole.</p>

<p>Denoting the radius of the event horizon $r_\mathrm{S}$ (for "Schwarzschild radius"), time runs slower by a factor of $(1 - r_\mathrm{S}/r)^{-1/2}$ for an observer at a distance of $r$. As $r$ approaches $r_\mathrm{S}$, this factor goes to infinity, i.e. the observer will never reach $r_\mathrm{S}$</p>

<p>However, this is only for the external observer; the falling observer would cross the horizon and reach the center in a finite time.</p>

<p>With respect to "not being stable", you're probably right that they are referring to Hawking radiation which presumably makes the black hole slowly "evaporate". Near $r_\mathrm{S}$, pairs of virtual particles are being created and can be turned into real particles by the gravitational field. If they avoid falling into the black hole, energy is taken away from the hole, reducing its mass.</p>

CC BY-SA 3.0
2015-06-03T06:56:01.283Z
2015-06-03T06:56:01.283Z
pela
<p>&quot;The magnetospheric eternally collapsing object (MECO) is an alternative model for black holes initially proposed by Indian scientist Abhas Mitra in 1998 and later generalized by American researchers Darryl J. Leiter and Stanley L. Robertson.&quot; -- <a href="https://en.wikipedia.org/wiki/Magnetospheric_eternally_collapsing_object" rel="nofollow noreferrer">Magnetospheric eternally collapsing object</a> @ Wikipedia</p>
<p>In a nutshell, general relativity prevents a black hole from forming: it would take an infinite amount of time for it to form.</p>
<p><a href="https://academic.oup.com/mnras/article/369/1/492/1058109" rel="nofollow noreferrer">Radiation pressure supported stars in Einstein gravity: eternally collapsing objects</a></p>
<p><a href="https://arxiv.org/abs/astro-ph/9803014" rel="nofollow noreferrer">Final State of Spherical Gravitational Collapse and Likely Source of Gamma Ray Bursts</a></p>

CC BY-SA 4.0
2022-08-21T18:37:45.073Z
MECO is a fringe theory, inconsistent with general relativity, and believed by almost no one.
benrg
CC BY-SA 4.0
2022-08-21T22:18:01.157Z
@benrg So? The OP asked what it was, not how popular it was.
shawnhcorey
CC BY-SA 4.0
2022-08-21T22:31:52.873Z
The OP only said "eternally collapsing", which could refer to the so-called river model, or to time dilation as pela mentioned in a comment. In any case, your summary of MECO ("in a nutshell, GR prevents a black hole from forming") is incorrect since MECO is not GR.
benrg
CC BY-SA 4.0
2022-08-22T08:05:36.753Z
@benrg I believe this answer is fine, as long as it clearly specifies that it talks about an alternative model that is incompatible with general relativity. After all, _this_ might be the theory that the OP reported being pointed out by some scientists.
Prallax
CC BY-SA 4.0
2022-08-21T10:56:44.910Z
2022-08-21T14:38:54.303Z
2022-08-21T14:38:54.303Z
shawnhcorey
<p>As has been pointed out by some scientists, that black holes aren't stable bodies but are eternally collapsing objects. How does one come to such a conclusion? Is hawking radiation related to this in some way?</p>

CC BY-SA 3.0
2015-06-02T07:42:12.187Z
Wrt "eternally collapsing", they are probably referrring to the fact that in the reference farme of an external observer, time dilation prohibits matter from ever reaching the event horizon (the "surface") of the black hole. However, this is only for the external observer; an observer falling with the collapsing matter would cross the horizon and reach the center in a finite time. Wrt "not being stable", you're probably right that they are referring to Hawking radiation which presumably makes the black hole slowly "evaporate".
pela
CC BY-SA 3.0
2015-09-01T10:25:45.503Z
As to your first question, it's very similar to this one:  http://physics.stackexchange.com/questions/5031/can-black-holes-form-in-a-finite-amount-of-time   As for your 2nd question, that's a no.  The eternal collapse which may not be true (except from the point of view of an observer - see Pela's answer) and the Hawking radiation are entirely separate things.
userLTK
<black-hole><hawking-radiation>
Eternally collapsing objects?
Victor Juliet
# Eternally collapsing objects?

(Asked by: username_0 on 2015-06-02)

As has been pointed out by some scientists, that black holes aren't stable bodies but are eternally collapsing objects. How does one come to such a conclusion? Is hawking radiation related to this in some way?

**Tags:** black-hole, hawking-radiation

> **Comments:**
> **username_1**: Wrt "eternally collapsing", they are probably referrring to the fact that in the reference farme of an external observer, time dilation prohibits matter from ever reaching the event horizon (the "surface") of the black hole. However, this is only for the external observer; an observer falling with the collapsing matter would cross the horizon and reach the center in a finite time. Wrt "not being stable", you're probably right that they are referring to Hawking radiation which presumably makes the black hole slowly "evaporate".  
> **username_2**: As to your first question, it's very similar to this one:  http://physics.stackexchange.com/questions/5031/can-black-holes-form-in-a-finite-amount-of-time   As for your 2nd question, that's a no.  The eternal collapse which may not be true (except from the point of view of an observer - see username_1's answer) and the Hawking radiation are entirely separate things.  

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## 2 answers

### Answer by username_1 on 2015-06-03. Score: 4

With respect to "eternally collapsing", they are probably referrring to the fact that in the reference frame of an external observer, gravitational time dilation prohibits matter from ever reaching the event horizon (the "surface") of the black hole.

Denoting the radius of the event horizon $r\_\mathrm{S}$ (for "Schwarzschild radius"), time runs slower by a factor of $(1 - r\_\mathrm{S}/r)^{-1/2}$ for an observer at a distance of $r$. As $r$ approaches $r\_\mathrm{S}$, this factor goes to infinity, i.e. the observer will never reach $r\_\mathrm{S}$

However, this is only for the external observer; the falling observer would cross the horizon and reach the center in a finite time.

With respect to "not being stable", you're probably right that they are referring to Hawking radiation which presumably makes the black hole slowly "evaporate". Near $r\_\mathrm{S}$, pairs of virtual particles are being created and can be turned into real particles by the gravitational field. If they avoid falling into the black hole, energy is taken away from the hole, reducing its mass.


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### Answer by username_3 on 2022-08-21. Score: 0

"The magnetospheric eternally collapsing object (MECO) is an alternative model for black holes initially proposed by Indian scientist Abhas Mitra in 1998 and later generalized by American researchers Darryl J. Leiter and Stanley L. Robertson." -- [Magnetospheric eternally collapsing object](https://en.wikipedia.org/wiki/Magnetospheric_eternally_collapsing_object) @ Wikipedia

In a nutshell, general relativity prevents a black hole from forming: it would take an infinite amount of time for it to form.

[Radiation pressure supported stars in Einstein gravity: eternally collapsing objects](https://academic.oup.com/mnras/article/369/1/492/1058109)

[Final State of Spherical Gravitational Collapse and Likely Source of Gamma Ray Bursts](https://arxiv.org/abs/astro-ph/9803014)

> **Comments:**
> **username_4**: MECO is a fringe theory, inconsistent with general relativity, and believed by almost no one.  
> **username_3**: @username_4 So? The OP asked what it was, not how popular it was.  
> **username_4**: The OP only said "eternally collapsing", which could refer to the so-called river model, or to time dilation as username_1 mentioned in a comment. In any case, your summary of MECO ("in a nutshell, GR prevents a black hole from forming") is incorrect since MECO is not GR.  
> **username_5**: @username_4 I believe this answer is fine, as long as it clearly specifies that it talks about an alternative model that is incompatible with general relativity. After all, _this_ might be the theory that the OP reported being pointed out by some scientists.  

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