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I have seen articles about the Milky Way's "gentle giant" black hole. For example:

Both of these articles say the black hole is not eating very much matter, which is the only clue I have from the articles.

A similar phrase, "gentle singularity," is used in the movie Interstellar. There has been some discussion about that, in which the consensus seems to be that the size of a supermassive black hole reduces the tidal forces at the event horizon, such that a falling entity would not be spaghettified. (I acknowledge that a movie quote is far from authoritative.)

So I have two hints at a definition of "gentle giant" black hole:

  1. A black hole that consumes little matter.
  2. A supermassive black hole whose tidal forces will not cause spaghettification.

Is either of these correct? If not, is there an authoritative definition of a "gentle giant" black hole?

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    $\begingroup$ It sounds very much like newspaper science popularization language, and probably means 1 in these cases, but all supermassive black holes do fall in category 2 too. $\endgroup$
    – Anders Sandberg
    Commented Sep 11, 2023 at 20:12
  • $\begingroup$ Black hole expert Kip Thorne was a consultant for Interstellar, but they had to "bend" the physics a little for storytelling purposes. See physics.stackexchange.com/q/148567/123208 $\endgroup$
    – PM 2Ring
    Commented Sep 12, 2023 at 7:38

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There's no "authoritative" definition, this is just the common meaning of the word "gentle" used in a popular science and science fiction context.

A black hole might be gentle because the tidal forces at its horizon are gentle (supermassive black holes have gentle tides at their event horizon, but rapidly more extreme tides beyond the event horizon (and once you cross, you can't come back). Black holes without a hot accretion disc won't be emitting large amounts of harsh radiation, again relatively "gentle".

I can find one mention of "gentle black hole" in the literature: The quantum gravitational black hole is neither black nor white, which contrasts the stable (and hence "gentle") Schwarzschild state with a dynamic model of quantum gravitational collapse.

So in conclusion, no, there is no authoritative definition of "gentle" when applied to a black hole.

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