If planet 9 is not a planet but a black hole how can we find it? Can we see gravitational lense or infrared/gamma light?

  • $\begingroup$ I'd presume that microlensing events, if you looked in the right place at the right time, would be possible. $\endgroup$
    – WarpPrime
    Commented Jan 13, 2022 at 14:52
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    $\begingroup$ And for a sense of scale, we'd be talking about a BH roughly the size of a softball or large orange. $\endgroup$
    – eps
    Commented Jan 13, 2022 at 15:02
  • $\begingroup$ Its impossible to any blackhole if it is "silent". Although its still a tough job to detect supermassive blackholes, In your case difficulty of detecting a black hole of radius just 4.4 cm with an optical ground telescope depends on how far it is away from the sun. Gravitational lensing will help $\endgroup$ Commented Jan 13, 2022 at 15:04
  • $\begingroup$ Does this answer your question? How would a small nearby black hole be detected and confirmed as such? See also: astronomy.stackexchange.com/questions/27983/… and astronomy.stackexchange.com/a/36882/2531 $\endgroup$
    – ProfRob
    Commented Jan 13, 2022 at 15:25


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