How big is a black hole? · HackerPapers discussions

How big is a black hole? — mentioned by raattgift

Wed, 28 May 2025 17:42:04 GMT

The mean density of the interior is much much much lower than you think, because the Schwarzschild interior volume is enormously larger than that of a closed Euclidean 3-ball of the Schwarzschild radius. Some details: Christodoulou & Rovelli 2014 showed that the maximal interior volume of a Schwarzschild black hole increases with time <https://arxiv.org/abs/1411.2854>. There is plenty of follow-on work in the literature for other varieties of black hole, and it is pretty generic that a black hole gets REALLY BIG inside as it gets older. I have previously aimed HNers at DiNunno & Matzner 2008…

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How big is a black hole? — mentioned by raattgift

Thu, 24 Oct 2024 11:48:02 GMT

The area of the Sun and the Earth and every other self-gravitating body in hydrostatic equilibrium is also proportional to the body's mass. Volumes are weird though: unlike area, relativistic volume can depend on the body's (and the spacetime's) history and composition rather than just the body's mass. In general the spatial volumes inside massive bodies in curved spacetime are larger than in Euclidean-Newtonian space. The volume deviation is carried in the Ricci tensor https://en.wikipedia.org/wiki/Ricci_curvature#Direct_geometr... http://arxiv.org/pdf/gr-qc/0401099v1 (section 5.2)…

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How big is a black hole? — mentioned by raattgift

Mon, 08 Apr 2024 17:30:29 GMT

>> any object can become a black hole if it is made dense enough [big 'if'!] > any material (of any density) can be made a black hole if there is enough of it There is an awful lot of intergalactic medium out there. It's of "any density" (albeit very low). How come it's not a black hole? Isn't there "enough of it"? (cf. the "missing baryons problem"). There is an awful lot of atomic and molecular hydrogen gas in the Milky Way and practically every other galaxy. In our galaxy it totally dwarfs all the matter in our central black hole, the stellar black holes, and in all the luminous stars…

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How big is a black hole? — mentioned by raattgift

Sat, 07 Sep 2019 14:34:42 GMT

Unfortunately, Rovelli & Christodolou show [ https://arxiv.org/abs/1411.2854 ] that: independent of coordinate choice, the spatial 3-volume of a static Schwarzschild BH departs spectacularly from Euclidean geometry (not surprising); and in a collapsar asymptoting to Schwarzschild, volume increases over time up to some maximum (depending on Hawking radiation). More generally, one cannot rely on intuitions from Euclidean relations in substantially non-Euclidean geometries -- and where there is Ricci curvature, we depart from Euclid. Y C Ong has a perhaps slightly more accessible overview and…

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How big is a black hole? — mentioned by raattgift

Sat, 08 Dec 2018 16:29:14 GMT

Neglecting evaporation, it's a lot closer to Yen Chin Ong's results (and those he cites, especially Christodoulou and Rovelli [2]) than most of the comments throughout this discussion, in that with a careful choice of time coordinate a spacelike spherical sector of a Schwarzschild black hole could evolve roughly similarly. Of course, one has enormous freedom to choose spacelike hypersurfaces through a Schwarzschild black hole, so such a result is not especially interesting without some sort of uniqueness proof for the idea, and I don't think that's achievable. (cf [2]). I'm also not sure this…

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