Do Black Holes *actually* exist?

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Discussion Overview

The discussion centers around the existence of black holes, exploring both theoretical and observational perspectives. Participants examine the implications of general relativity (GR) and quantum mechanics (QM) on black hole formation, characteristics, and the nature of singularities. The conversation includes references to specific astronomical observations and theoretical models.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants argue against the physical existence of black holes, citing claims that matter cannot collapse into a point and referencing the Heisenberg uncertainty principle as a limiting factor.
  • Others assert that black holes, particularly their event horizons, are supported by both theoretical predictions and observational evidence, such as the detection of gravitational lensing and the behavior of stars around Sagittarius A*.
  • A participant suggests that while GR predicts singularities, the nature of these singularities remains uncertain and may not exist as traditionally conceived.
  • There is a proposal that the singularity in a Kerr black hole could be viewed as a spacetime tube with quantum implications, including the potential for Hawking radiation resulting from quantum tunneling.
  • Some participants differentiate between the existence of black holes and the existence of singularities, suggesting that the former may be accepted while the latter remains contentious.
  • Concerns are raised about the limitations of GR in describing black holes, with suggestions that quantum mechanics may impose constraints on the minimum size of a singularity.
  • Observational evidence is cited, including studies of stars orbiting a massive object at the center of the Milky Way, which some participants argue supports the existence of black holes.

Areas of Agreement / Disagreement

Participants express a mix of agreement and disagreement. While there is some consensus on the observational evidence for black holes, significant debate exists regarding the nature of singularities and the compatibility of GR and QM in this context. The discussion remains unresolved on several key points.

Contextual Notes

Participants note that the definitions of black holes and singularities are crucial to the discussion, and there are unresolved questions about the implications of quantum mechanics on the nature of singularities and event horizons.

Who May Find This Useful

This discussion may be of interest to those studying astrophysics, theoretical physics, or anyone curious about the intersection of general relativity and quantum mechanics in the context of black holes.

  • #31
You may find sonic event horizons interesting. It's basically a phenomenological test of GR. The most interesting part of this is space, time and gravity appears to be emergent properties of the universe. I find that highly interesting.
 
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  • #32
That does sound interesting Chronos. Could you post some articles on it?
 
  • #33
morghen said:
I don't get the negativism and the will to say it isn't so on this forum. What exactly has been observed or measured about the Hawking radiation? Nothing..or not much. So we don't know much about it yet you're sure it won't give us information about what's beyound the EH. How can you narrow your mind so much to exclude the fact that even if the radiation is coming from a surface outwards its characteristics can hint us on what's behind it? Perhaps there are differences in the characteristics of the radiation between BHs or between the studied portion on the EH. Perhaps there is something to it...perhaps not. But being one of the few things we think we know abou the BHs its narrow minded to say, NO it does not matter, we will not look into it.

Good day.

Because what MIGHT happen doesn't matter. There are an infinite amount of possibilities when talking about something that hasn't been observed, so unless we narrow it down to what we think SHOULD happen, what we believe will PROBABLY happen, we can't have a meaningful discussion. According to the model and the math, hawking radiation shouldn't tell us anything about what's behind the event horizon. Will it? Can it? We have no idea. But IF our current knowledge of black holes is sufficiently accurate, it will not. At least as far as I know.
 
  • #34
morghen said:
I don't get the negativism and the will to say it isn't so on this forum. What exactly has been observed or measured about the Hawking radiation? Nothing..or not much. So we don't know much about it yet you're sure it won't give us information about what's beyound the EH. How can you narrow your mind so much to exclude the fact that even if the radiation is coming from a surface outwards its characteristics can hint us on what's behind it? Perhaps there are differences in the characteristics of the radiation between BHs or between the studied portion on the EH. Perhaps there is something to it...perhaps not. But being one of the few things we think we know abou the BHs its narrow minded to say, NO it does not matter, we will not look into it.

Good day.

Let me explain some aspects of Hawking radiation. For one its a process of virtual particle pair creation where one of the pairs falls into the BH. This particle is lost to us. The other particle becomes part of the blackbody temperature. All this occurs outside the event horizon and does not originate inside the BH.

Now the part where Hawking states that BH's will eventually radiate and decrease in size has to do with tachyons. First I should point out that this is an extremely slow process. A process slower than the entire history of the universe. The exact magnitude Id have to look up.
I should also note is the tachyon is only theorized and has never been measured in any process.
Hence its not part of our standard model. However even if
we did discover tachyons it still would not provide any information on what's inside a BH.
Hope this helps
 
  • #35
If BH's did not exist, how could one explain the orbits of stars at the center of the Milky Way? I don't know enough about them, but I haven't read that Neutron Stars, Magnetars, or Quark Stars(?) would be capable of making stars orbit at several million miles per hour.

Also, wouldn't the entire orbit of the Milky Way (or any galaxy centered around a supermassive Black Hole) be a big question as well?
 
  • #36
enceladus_ said:
If BH's did not exist, how could one explain the orbits of stars at the center of the Milky Way? I don't know enough about them, but I haven't read that Neutron Stars, Magnetars, or Quark Stars(?) would be capable of making stars orbit at several million miles per hour.

There is no doubt that something with a million or more solar masses sits at the center of our galaxy. Whether it has an event horizon and is in fact a black hole is unknown, we just have absolutely no other explanation. Everything we know about gravity says there should be an actual black hole. We just have yet to confirm it.

Also, wouldn't the entire orbit of the Milky Way (or any galaxy centered around a supermassive Black Hole) be a big question as well?

Not really. Like I said, the mass is there, the only question is if it's tied up in a black hole or not.
 
  • #37
How could we account for quasars, and the large numbers of quasars we observe then?
 
  • #38
Drakkith's reply pretty much describes the distinction. The existence of an EH is one of the main distinquishments between a BH and a neutron star.
Both have an acrettion disk with jets. Both can also have an apparent horizon.
 
  • #39
To expand further one of yhe key differences between a BH and a neutron star is how it collapses. In both cases the process is the same. However in a neutron star the mass is not enough to overpower the strong nuclear force so the collapse stops.
In the case of a BH the collapse continues. When that collapse falls below its schwartchild radius an event horizon forms.
In both cases A BH and a neutron star exhibite similar properties and are extremely hard to distinquish between one or the other.
 
  • #40
There are an estimated 100 million neutron stars in our galaxy. We have detected about 1000 of them. Needless to say they are not easy to detect ane most are pulsars. Black holes are even more difficult to detect. We have only circumstantial evidence for their existence. Save for the supermassive black hole at the center of our galaxy, Cygnus X-1 we only have a handful of strong candidates in our galaxy.
 
  • #41
Mordred said:
Drakkith's reply pretty much describes the distinction. The existence of an EH is one of the main distinquishments between a BH and a neutron star.
Both have an acrettion disk with jets. Both can also have an apparent horizon.

The apparent horizon is inside the event horizon. Thus this statement is mathematically false in GR. If you are referring to some other theory and definition of apparent horizon, please provide a reference.
 
  • #42
Your correct, not sure why I included apparent horizon.
 
  • #43
Sgr, not Cyg

Cygnus X-1 is a very strong candidate black hole, but it is not the one in the center of the Galaxy, which is Sagittarius X-1. Cyg X-1 is thought to be about 10-15 solar masses and Sgr X-1 is thought to be around four million solar masses. There really are only a dozen or two good stellar mass black hole candidates known in our galaxy, all in binaries.
 
  • #44
jimgraber said:
Cygnus X-1 is a very strong candidate black hole, but it is not the one in the center of the Galaxy, which is Sagittarius A*.

fixed
 

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