Black hole traveling near the speed of light

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Discussion Overview

The discussion centers around the implications of a black hole traveling at relativistic speeds, specifically near the speed of light. Participants explore the geometry of the black hole's event horizon from different observational perspectives, the effects of relativistic motion on its appearance, and the nature of gravitational effects in this context. The conversation touches on theoretical aspects of general relativity and the challenges of visualizing black holes under such conditions.

Discussion Character

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

Main Points Raised

  • Some participants propose that the event horizon of a black hole traveling at relativistic speeds may appear length contracted, potentially resembling a black disk from certain viewpoints.
  • Others argue that the geometry of the event horizon is fundamentally different due to it being generated by null curves, complicating the application of length contraction concepts typically reserved for timelike objects.
  • A participant notes that while the event horizon cannot be directly observed, the effects of objects falling into the black hole may create observable phenomena, such as lensing.
  • One participant questions the implications of relativistic mass increase on the black hole's gravity and the experience of time for objects falling into it, suggesting a need for clarity on these concepts.
  • Another participant emphasizes that relativistic mass does not influence gravitational effects in general relativity, as the mass of the black hole is invariant.
  • There is a discussion about the Schwarzschild geometry and how it might appear in a frame where the black hole is moving rapidly, with some participants expressing confusion over the implications of null curves in this context.
  • One participant raises a scenario involving signal redshift and blueshift as a black hole accelerates, questioning how these effects might interact from different frames of reference.

Areas of Agreement / Disagreement

Participants express a range of views on the nature of the event horizon and its geometry under relativistic motion, with no consensus reached on how to interpret these effects. The discussion remains unresolved regarding the application of length contraction and the implications of relativistic speeds on gravitational properties.

Contextual Notes

Limitations include the complexity of visualizing black holes at relativistic speeds, the dependence on definitions of motion and geometry, and the unresolved nature of how different frames perceive the event horizon.

  • #31
rootone said:
The black hole is approaching a speed of c in relation to what?
To the observer
 
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  • #32
To the observer.
... technically you can't just say "the observer" in GR like you can with SR. In SR the observer is usually inertial. Where a black hole is involved, the observer is unlikely to be inertial so you'll see discussion involving distant and close observers, observers free-falling, and so on. Do you mean to ask about a relativistic black hole from the POV of a very distant observer? Perhaps headed directly away or directly towards the observer? Or are you thinking of a black hole passing by so it starts out distant, comes close, but not s close the observer gets gravitationally bound to it, and then retreats?

Did you have a look at the 10-things article about black holes? (See link post 29 above.) - the object that gets observed is probably not going to be a black ball for instance. What are you referring to when you talk about a black hole - the event horizon or the collapsed object that causes the event horizon ... or maybe you mean the light from the accretion disk or the optical effect on the background stars?

As you refine your question - you'll be able to get a better idea of the answers.
 

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