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by MrEldritch
2822 days ago
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I would argue that "position" and "linear momentum" are more properties of one's particular choice of inertial reference frame than properties of the black hole itself specifically. And yes, angular momentum has three scalar components, but it's also one single vector. "Mass, charge, and angular momentum" makes three properties. >at timescales less than light-crossing there can be substantial additional hair. Ahh, thank you - that clears up some misconceptions of mine that have always confused me, like "Wait, so if black holes have no hair, how can they wobble and ring-down and produce gravitational waves after a black hole merger?" |
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Ditch that when thinking about black holes.
A BH's position in a general curved spacetime can be described by many arbitrary coordinate systems, but a black hole spacetime is not flat spacetime (by definition!) so special relativistic ideas involving frames of reference tend to fail pretty spectacularly.
As to linear and angular momentum and balding, I rather like these four sentences from Hawking & Penrose, "What the no-hair theorems show is that a large amount of information is lost when a body collapses to form a black hole. The collapsing body is described by a very large number of parameters. These are the types of matter and the multipole moments of the mass distribution. Yet the black hole that forms is completely independent of the type of matter and rapidly loses all the multipole moments except the first two: the monopole moment, which is the mass, and the dipole moment, which is the angular momentum." [1]
Merging black holes, from sufficient distance that resolving them individually is difficult, look very much like a collapsing body.
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[1] https://books.google.co.uk/books?id=6a-agBFWuyQC&lpg=PA39&pg... at the bottom of the page.