What would the Penrose Diagram look like that represented a black hole (call it Black Hole-B), inside of a massive black hole (Black Hole-A), in our universe?

and, as inside of the Penrose diagram for BH-A (PD-1), would be attached to the upper diagonal edge of our universe's Penrose Diagram (PD-0), a) Would the Penrose diagram for BH-B (PD-2), lie along the upper diagonal edge of PD-1, (the Penrose Diagram for BH-A)?

and, since radial "Space-Like" direction lines? in PD-0 become "Time-like" in PD-1, and vice versa, would they then switch back in PD-2 and revert back to the way they were in our own universe?

  • $\begingroup$ Actually, I was only asking how the penrose diagram would look... My assumptions are only that you can have a black hole inside our visible universe, and, if it is true (as posited by the descriptions I have read, that from the perspective of someone who has fallen into a black hole, that he/she is in ordinary 4-D space time, similar to our own, that a black hole can form in that space time, then how would the Penrose diagram (and the geodesics within it), for that tripley-nested scenario look? $\endgroup$ Commented Oct 23, 2023 at 15:09
  • $\begingroup$ First, thanks for your time!. But I know that for two black holes in our space time, that one cannot fall into the other. But if the laws of Physics in the interior of a black hole are in fact (from the perspective of an observer in the interior), identical to the laws of Physics in our space-time), then if sufficient matter within the black hole's interior collapsed to within its Schwartzchild radius, it would indeed form a black hole inside of that black hole, no? $\endgroup$ Commented Oct 23, 2023 at 15:13
  • $\begingroup$ I think this is a good question. I've even seen a paper saying that inside a very large and rotating BH, stable orbits can exist. Is it possible for a star to inhabit such an orbit, and then undergo collapse into a 2nd BH? $\endgroup$
    – RC_23
    Commented Oct 23, 2023 at 20:21
  • $\begingroup$ @safesphere, I edited to clarify.. I am asking this to clarify what I see as possible inconsistency. Some ideas I have seen presented by fairly well-respected individuals imply that an observer who falls through event horizon of a very very large Black Hole would not percieve anything unusual.... but the way they describe the switching of space-like and time-like direction lines belies that. $\endgroup$ Commented Oct 24, 2023 at 23:43
  • $\begingroup$ @Charles the statement is true about an observer perceiving nothing unusual in his local vicinity, provided that vicinity is small enough that the local gravity field is uniform. The $r$ coordinate becoming timelike is a coordinate-dependent effect. As a general principle, in an observer's local vicinity the spacetime is always Minkowskian (or can be written as such) $\endgroup$
    – RC_23
    Commented Oct 24, 2023 at 23:55


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