Could an object survive passing through two intersecting black holes?

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Discussion Overview

The discussion explores the theoretical possibility of an object, specifically a proton, passing through two intersecting black holes and the implications of being at a point of equal forces between them. It delves into concepts of event horizons, gravitational forces, and the behavior of particles under extreme conditions, touching on both theoretical and conceptual aspects of black hole physics.

Discussion Character

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

Main Points Raised

  • Some participants question whether an object can pass through two event horizons of intersecting black holes and what would happen to a proton in such a scenario.
  • One participant clarifies that an event horizon is a property of spacetime and argues that two event horizons cannot intersect, suggesting a single event horizon forms instead.
  • Another participant discusses the implications of being at a point where forces are equal, noting that in a specific frame of reference, the gravitational force on the proton could be zero, leading to no effect.
  • There is mention of tidal forces and Ricci curvature, with one participant stating that the tidal forces near a solar-mass black hole's event horizon are insufficient to affect the proton until it is very close to a singularity.
  • One participant acknowledges the mathematical nature of event horizons and introduces the idea of a sphere of photons potentially surrounding an event horizon under certain conditions.
  • Another participant describes the process by which event horizons deform and merge, ultimately leading to a unified shape, which challenges the notion of passing through two separate horizons.

Areas of Agreement / Disagreement

Participants express differing views on the nature of event horizons and the feasibility of passing through them. While some agree on the mathematical properties of event horizons, there is no consensus on the implications for an object like a proton in the vicinity of two black holes.

Contextual Notes

Limitations include the dependence on specific frames of reference and the unresolved nature of how forces act on particles in extreme gravitational fields. The discussion does not resolve the complexities surrounding the behavior of particles near black holes.

BkBkBk
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Would it be possible for something to pass through 2 event horizons,falling into both black holes?
also,if it can,what would happen if the objecct in question (lets say a proton) was at a point where the forces acting on it were equal in every direction?

say being at the centre of these two circles?(even though the forces wouldn't be equal at this point.

http://www.csnmail.net/~stjoan5/venn2.1.gif

would the proton quickly expand into a quark-gluon plasma?or would the gravitational/strong forces keep it confined?
 
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An event horizon isn't a physical piece of a physical object. An event horizon is a property of a spacetime as a whole. When you have a spacetime that becomes flat at infinity, and there's a set of events that can't be causally connected to future events at infinity, then the event horizon is the boundary of that set. So by definition, it's not possible to have two event horizons that intersect, as in your drawing. Your pair of black holes will have a single event horizon, roughly corresponding the outer, dog-bone-shaped outline of your drawing.

BkBkBk said:
also,if it can,what would happen if the objecct in question (lets say a proton) was at a point where the forces acting on it were equal in every direction? would the proton quickly expand into a quark-gluon plasma? or would the gravitational/strong forces keep it confined?
In a frame of reference tied to the center of mass of the black hole system, the gravitational force on your proton is zero by symmetry, so it will produce no effect at all. If you pick a different frame of reference, accelerating relative to the first, then you can make the force on the proton be anything you like. This is always true in GR; the gravitational field can be whatever you like, depending on your frame of reference. This shows that the gravitational field, or gravitational forces, are not particularly useful concept in GR.

What could have a dramatic effect on the proton would be a very high tidal force (high Ricci curvature). For, say, solar-mass black holes, the tidal forces near the event horizon are far too small to have such an effect on the proton. The proton would not be ripped apart until it was very, very close to one of the singularities.
 
bcrowell said:
An event horizon isn't a physical piece of a physical object. An event horizon is a property of a spacetime as a whole.

i get that its not an object in a physics sense,and that its a mathematical limit(although i have read somewhere that there's a possibility that there could be a sphere of photons surrounding the event horizon as long as the black hole didnt get more massive,just because their incoming angle and speed was just right that they took orbit)

ok it makes sense now i think about it as limit,thank you.
 
A probably unrelated note: The above configuration of event horizons never arises. What happens is the event horizons slowly deform until they finally connect through a small "bridge" which then expands into one uniform peanut-like shape, and finally settles down to a sphere.

I suppose it is slightly relevant because the concept of "passing through two event horizons" no longer works, as there is just one unified horizon.
 

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