Black hole collapse - ray tracing

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Discussion Overview

The discussion revolves around the ray tracing of light in the context of black hole collapse models, specifically focusing on Oppenheimer-Snyder and Vaidya metrics. Participants explore the implications of these models on light rays from distant emitters as observed by distant observers, considering both theoretical and simulated aspects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the availability of reliable ray tracing results for collapse models like Oppenheimer-Snyder or Vaidya, contrasting them with static Schwarzschild black holes.
  • Another participant seeks clarification on what is meant by "ray tracing results," suggesting it could refer to mathematical theorems, simulated images, or characterizations of possible orbits.
  • There is a suggestion that the geodesics in the Vaidya metric might align with the trajectories of infalling matter, implying a connection between ray tracing and the dynamics of the collapse.
  • One participant posits that ray tracing could be understood as null geodesics, indicating that the Schwarzschild and Oppenheimer-Snyder metrics might yield similar results under certain conditions.
  • Another participant expresses interest in the specific images of rays passing through a dust ball and those close to the event horizon as the collapse progresses.
  • Discussion includes the potential for realistic simulations of black holes, with a focus on the feasibility of resolving the event horizon of Sagittarius A* using infrared observations.
  • A reference is made to a friend's investigation into Kerr black holes and accretion discs, suggesting ongoing research in related areas.

Areas of Agreement / Disagreement

Participants express various viewpoints regarding the nature of ray tracing in black hole collapse models, with no clear consensus on the specifics of the results or the implications of the different metrics discussed.

Contextual Notes

Participants acknowledge the complexity of the metrics involved and the conditions under which comparisons can be made, particularly regarding the behavior of light in the vicinity of collapsing black holes.

tom.stoer
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I know several raytraycing results for static Schwarzschild black holes, but I have never seen something similar for collapse models like Oppenheimer-Snyder or Vaidya.

Are there reliable raytraycing results showing the effect on light rays from far distant light emitters observed by (far distant) observers?
 
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no ideas?
 
push
 
What do you mean by raytracing results? Mathematical theorems? Simulated images? Characterizations of possible orbits? The Vaidya metric represents the collapse of a field of incoherent radiation, so I would think that the geodesics would be the same as the trajectories of the infalling matter, which would also be the same as the rays in an optical simulation.

Is this of any interest? Seahra, "An introduction to black holes," http://www.math.unb.ca/~seahra/resources/notes/black_holes.pdf Has a bunch of discussion of horizons in the Vaidya metric.
 
Assuming I'm right in thinking that ray tracing is just null geodesics, the static schwarzschild should be the same as oppenheimer-snyder if you make sure light only passes in the external part of the metric, as the metric is the same.

I'm guessing this may not be particularly helpful, though.
 
Last edited:
pervect said:
Assuming I'm right in thinking that ray tracing is just null geodesics, the static schwarzschild should be the same as oppenheimer-snyder if you make sure light only passes in the external part of the metric, as the metric is the same.
Yes.

The Schwarzschild portion is growing with t to smaller r(t), therefore the images of rays not crossing r(t) are rays like in Schwarzschild spacetime with smaller r(t) but constant mass M.

But what I am especially interested in is the image of rays
a) passing through the dust ball (assuming that the dust is transparent)
b) close to r(t) in the far future where r(t) → 2M asymptotically
 
So realistic simulations of what might be seen through a telescope? I think the studies so far have been studies of the feasibility of resolving the event horizon of Sag A* using infrared. I would be surprised if anyone had tried simulating anything else, because Sag A* is the only realistic prospect for us to resolve.
 

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