A question of mine was closed on the grounds of being non-mainstream. Mainstream is defined below:

Mainstream physics is physics which has been accepted by a significant portion of the physics community. In the case of modern physics, if a theory has not been published in a reputable journal, it is not considered mainstream.

This definition having been written in a community answer (87 % Manishearth) to this meta question.

My question asks at what point a black hole would leave Earth uninhabitable in its approach. More specifically, I asked for an upper and lower limit, as the point it would leave Earth uninhabitable would depend on the characteristics of the black hole.

The only criticisms I got in the comments were about how a black hole wouldn't affect the solar system any differently than another object of the same mass. Now this may be true, and I posted a comment displaying willingness to edit my question to be more general if someone posted an answer showing how this is the case (though this was done after the question was closed). I get that an unnecessarily specific question is sub-par, but it is surely not grounds for closing, as it creates opportunity for more learning (they could dismantle any notion that black holes are any scarier than a passing, rogue star or something). Also, I was basing my assumptions that a black hole would decimate us differently than other massive objects on a comment made on an answer (by Fraxinus) to a question of mine on the Astronomy.SE site.

However, I may have misunderstood something, but I don't see how the criticism I received in the comments is of the type you question isn't mainstream. If this is the case, if my question was closed on different grounds than the criticisms in the comments, then I'd like to receive an explanation for this. Basically, more core question is this: How is my question not mainstream? Is it not a fact approved by the mainstream in physics, that a black hole passing through the solar system could leave earth uninhabitable? Or is this idea a crackpot hypothesis? Or is it a component of my question that is non-mainstream, like the part about x-ray radiation?

EDIT: As user rob mentioned in the comments, some users chose "Needs details or clarity" as their close-vote reason. Again though, I don't see how my question is unclear. Given how this wasn't the main reason for their close, it shouldn't be the main question here either, but if anyone wants to answer how my question was unclear as well, that'd be great.


2 Answers 2


I for one think the question is unclear or too broad.

“Inhabitable” is not really defined, and actually hard to define. One can imagine the surface of the Earth is cold but that doesn’t make it uninhabitable: some animals may thrive.

The physics side is also vague. You do not specify anything about the black hole or its orbital parameter, so there is probably a continuous range of solutions.

Finally, it seems to me this question is a poor fit to the site: a reasonable answer would probably take pages of computation and a non-trivial simulation on which you give no guidance whatsoever.

Asking for an estimate of the distance at which tidal forces due to a black hole of given mass would break up the Earth is a better defined problem, although I would not know how to answer this myself. At least this removes the issue of estimating timescales over which ecological factors would change enough to make the Earth inhabitable.

  • 2
    $\begingroup$ " You do not specify anything about the black hole or its orbital parameter, so there is probably a continuous range of solutions." Of course, I mentioned this in my question, asking for the upper and lower limit of this continuous range. "(...) a non-trivial simulation on which you give no guidance whatsoever." Not sure what you mean with non-trivial, but I think you mean "lots of work"? If so, yeah, but an answer requiring much effort doesn't make it off-topic. It may limit interest, but that's okay. That could prompt me to put a bounty on it, which would reward any effort put into it. $\endgroup$
    – A. Kvåle
    Jul 25, 2021 at 0:44
  • $\begingroup$ As for "(...) you give no guidence whatsoever", I think you're referring to the lack of specification in regards to the BH's parameters. That point of criticism was covered in the first comment. If this is not what you meant, then could you please elaborate? "At least this removes the issue of estimating timescales over which ecological factors would change enough to make the Earth inhabitable." With this point you do bring up a weakness in my query, but I did touch on this by saying one was to ignore more complex ecological factors. $\endgroup$
    – A. Kvåle
    Jul 25, 2021 at 0:48
  • $\begingroup$ This of course creates the question of what is too complex, which is really the essence of the weakness. I think that the answerers may decide for themselves how much they want to take ecology into account, so long as they don't ignore an ecological change like the earth becoming -200 degrees or something. That's extreme. Less obvious climate changes and complex, chaotic ecological effects and consequences however, can be ignored, as they don't pertain to physics. I'm not sure if this boundary in my question was clear enough, but if not, this can be edited. $\endgroup$
    – A. Kvåle
    Jul 25, 2021 at 0:52
  • 2
    $\begingroup$ this is where it hurts: the answerers should not have to decide for themselves, else the question needs focus. Not sure why people voted for “non-mainstream”: it’s rather hypothetical in its current format and though not strictly “non-mainstream” hypotheticals sometimes collect vote-to-close as “non-mainstream”. I would have voted to close as unclear. $\endgroup$ Jul 25, 2021 at 1:29
  • $\begingroup$ it’s not enough to ask for an upper and lower bound. The size of BH is so variable that a super-massive one would yield a solution qualitatively different from a small one. $\endgroup$ Jul 25, 2021 at 1:32
  • $\begingroup$ but how can you ask a question on the ecological effects and expect answerers to decide what they want to take into account? $\endgroup$ Jul 25, 2021 at 13:02
  • $\begingroup$ @A.Kvåle I agree that your question is far too broad in its current state, and asking about stuff like X-rays from the accretion disk makes it even broader. If it's a typical stellar BH (rather than some tiny primordial BH), it would make a mess of the solar system. You'd need to run sims to determine exactly what it would do depending on its mass & trajectory. That's a topic for a paper, not a SE question, although I guess an answer could give a summary of the results of such sims. $\endgroup$
    – PM 2Ring
    Jul 26, 2021 at 7:15

I agree in full with @ZeroTheHero. Some additional points here. There are only a few canned options to choose when voting to close, so a person closing sometimes has to choose the best fit of several that could apply. I don't remember which of the choices I selected, but there are a couple of problems with this question:

  • There's no compelling evidence that I know for the idea that there are rogue black holes flying through the universe that are likely to pass through a solar system. (Not mainstream - there are some realistic arguments for BHs moving around, but the dynamics of that depends on the size and what formed them while none that I know suggest any sort of serious probability of hitting a distant solar system.)
  • If one did, then the comments that you referenced apply where, gravitationally, this wouldn't be different than any other massive object passing nearby unless you got especially close. (Just a fallacy of the original question.)
  • The other effects (X-rays, Hawking radiation, etc.) that you mentioned may or may not occur for a given black hole but the amount, directionality, etc. would depend a lot on the history and size of the specific black hole that happened to come through your solar system. (Not enough detail to answer, but probably also a case where if you give it enough detail you run further afoul of the first bullet.)
  • Even if we make assumptions for you on all of those, then you still want someone answering to get into how those factors would or would not combine to make Earth uninhabitable. (Not physics)

For what it's worth, I also think you misunderstood the answer on Astronomy.SE that you say prompted your question here, but taking that on too is too big of a scope for me now and in this forum. Even assuming that you did understand it, note that the answer that you've identified did exactly what we've mentioned here in order to formulate an answer at all: It locked in on a specific type of black hole, made assumptions about its accretion disk, ...

  • $\begingroup$ There are (probably) plenty of black holes travelling at high speed through the galaxy, although you're right that the odds of one visiting the solar system are very low. Supernova remnants often get a substantial natal kick. We don't have much data on single black holes, but we expect their velocities to be similar to those of pulsars. See en.wikipedia.org/wiki/Pulsar_kick & apod.nasa.gov/diamond_jubilee/papers/lamb/node3.html $\endgroup$
    – PM 2Ring
    Jul 26, 2021 at 14:36
  • $\begingroup$ I'm just saying that we expect that many stellar mass BHs have a high velocity relative to the galaxy, they don't just sit where they were formed. OTOH, simply due to geometry, many of these high velocity BHs & pulsars are heading out of the galactic plane, and so they aren't likely to disrupt any stellar systems. $\endgroup$
    – PM 2Ring
    Jul 26, 2021 at 14:58
  • $\begingroup$ @PM2Ring OK, I see your point and adjust the language in the answer. Was supposed to be an example not a definitive argument - I changed the language to be more general in that regard. $\endgroup$
    – Brick
    Jul 26, 2021 at 16:52

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