5
votes
Accepted
Why does rotation make black holes smaller?
First, let us note that “horizon radius” (at least when talking about black holes without spherical symmetry) is a coordinate dependent term, so it is better to use coordinate independent measure of ...
- 15k
4
votes
Why does rotation make black holes smaller?
isaacg asked: "Why does faster rotation shrink the outer event horizon?"
It doesn't. In terms of the irreducible mass $\rm \mathcal{M}$ and the cartesian radius $\rm R=\sqrt{x^2+y^2+z^2}$
$$...
- 10.4k
4
votes
How can the distance to the event horizon, as measured by a tape attached to a falling mass, be reconciled with the mass passing through it?
The answer you linked is about dangling a measuring tape above a black hole, not letting it fall freely. The end of the tape never crosses the event horizon, and its speed, relative to static ...
- 24.2k
3
votes
Accepted
Schwarzschild line element in Eddington-Finkelstein coordinates
What your are encountering here is a core feature of general relativity: time is inherently, and fundamentally a local quantity. While each observer will have an unambiguously defined local proper ...
- 10k
3
votes
Accepted
No hair theorem and Klein-Gordon equation
… what am I missing?
You are missing the meaning of (various) no-hair theorems. Those theorems are talking about equilibrium configurations corresponding to end points of gravitational collapse and ...
- 15k
3
votes
Accepted
Does the current size of the cosmological sound horizon play a relevant role in the universe?
The sound horizon is the same today as at recombination.
Before the time of recombination, the universe was full of free protons and electrons. Due to the electric charges of these particles, ...
- 2,648
2
votes
Can two relativistic black holes' event horizons overlap and separate again?
The Question: Arpad's initial query revolved around a cosmic conundrum. Given the significant momentum of two speeding black holes and their distant centers of gravity, how could a mere touch bring ...
1
vote
If, relative to us, objects never cross the event horizon, does this imply that we cannot observe a black hole grow?
The issue here is that you are combining ideas from two different spacetimes and arriving at a contradiction because the different spacetimes are different.
The first spacetime is the Schwarzschild ...
- 91.9k
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