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Astronomy

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  • $\begingroup$ Thank you. I always had the interpretation that singularities were a mathematical construct with no physical reality (not unlike a baseball diamond of size 400 square units, that has a side of 20 units, the other root of 400 being -20 but there is no physical distance of -20 other than the vector), and black holes were simply objects with an escape velocity above 300k km/s, neutron stars already reaching half of that. $\endgroup$
    – Mark Besser
    Commented Mar 27, 2021 at 16:32
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    $\begingroup$ A key fact about the interior of black holes is that spacial dimensions become "time-like" You have to go forward in time, you can't go back. Inside a black hole, you have to go forwards in space. There is no "backwards" or "away from the singularity" If something string-like happens to prevent ultimate collapse, then the final object would be very very small, probably much smaller than a single proton. We know enough about matter at larger scales and how gravity works to rule out any form of matter that we currently understand well. $\endgroup$
    – James K
    Commented Mar 27, 2021 at 16:38
  • $\begingroup$ The “from the outside it seems as if all the mass of the star is concentrated at one point” thing is misleading, Appearance of a black hole is highly symmetric (namely, a hole without angular momentum is spherically symmetric), but no reliable implications on where does “all the mass is concentrated” can be made of that. The gravity of any spherically symmetric (movement included) body is Schwarzschildean, right? m $\endgroup$
    – Incnis Mrsi
    Commented Jul 26, 2022 at 16:09
  • $\begingroup$ The “it seems as if all the mass of the star is concentrated at one point” thing is misleading, Outside appearance of a black hole is highly symmetric (namely, a hole without angular momentum is spherically symmetric), but no reliable implication on where does “all the mass is concentrated” ensues. The gravity of any spherically symmetric (movement included) body is Schwarzschildean, right? Moreover, spacetime of a hole resulting from collapse is different from ideal models (Schwarzschild, Kerr etc., having two event horizons, both future and past), and the former isn’t “vacuum” everywhere. $\endgroup$
    – Incnis Mrsi
    Commented Jul 26, 2022 at 16:51