Think of a spinning black hole. (Kerr black hole)

Every black hole has a point of infinite density, called a singularity.

When a singularity is spinning, does it have a different name? But when a point is spinning, it is still a point... So does it have a new name???


1 Answer 1


The particles in a black hole don't really converge to a point. The point isn't even there. There is litterally a hole in space towards which the particles are heading forever (from our point of view). Two particles falling in, one after another, will always be separated in the spacetime of the black hole. They are squeezed together though by the converging funnel. But in the length of the funnel they stay separated and they are experiencing less and less time. That is why it takes a finite time to infinity.

For a rotating black hole the infalling particles are dragged in the direction of rotation (frame dragging) and they end up not heading for the hole at infinity but a "ring-singularity" at infinity. That is, due to the rotation the width of the funnel will always be finite, not going to zero. So all particled end up around the central point (which itself isn't part of space). All particles end up on a ring around the center (the ring being part of a spherical 2D shape surrounding the center point). It's called a ring singularity. Though the space the ring is on is 2D.

  • 1
    $\begingroup$ So it's called a ring hole! Thank you for answering. $\endgroup$
    – hotgot100
    Jul 3, 2021 at 7:29
  • $\begingroup$ @hotgot100 Indeed! We just found a new name for it! $\endgroup$ Jul 3, 2021 at 7:32
  • $\begingroup$ Prishon, what is the name? Please tell me. $\endgroup$
    – hotgot100
    Jul 3, 2021 at 7:48
  • $\begingroup$ @hotgot100 It's a ring singularity. $\endgroup$ Jul 3, 2021 at 7:52

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