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It's perfectly safe to orbit a black hole - as long as you don't cross the event horizon, you're fine.

My questions is this: is there anything we could learn by doing so? Since nothing can escape a black hole's event horizon, it seems pointless to me. How am I wrong?

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  • $\begingroup$ It'd be pointless to go beyond the event horizon, certainly. Outside the event horizon, you might still be faced with overwhelming tidal forces, perhaps depending on the mass of the hole. $\endgroup$
    – Don Branson
    Sep 12, 2013 at 3:29
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    $\begingroup$ Sending a probe to a black hole, with out current technology would requires a long time though. Even nearby black hole (or suspected black holes) ares several thousand light-years distant. Examples: Cysgus X1 at 8000 ly, GRO J0422+32 =V518Per at over 4500 ly). Combine that with the speed we can give our probes and you will have to wait a LONG time before the probes arrive. That is assuming that we do not discover any faster technology in the next few centuries and that our future probes would not overtake our old/current-tech craft. $\endgroup$
    – Hennes
    Sep 12, 2013 at 11:52
  • $\begingroup$ @Hennes FWIW from our point of view a probe sent into the black hole will never cross the horizon. $\endgroup$
    – Manishearth
    Sep 12, 2013 at 12:14
  • $\begingroup$ I looked up how long it would take, did some math, and then discovered that this post had already answered how long it would take to get to a nearby black hole. $\endgroup$
    – Hennes
    Sep 12, 2013 at 12:41
  • $\begingroup$ +10 black holes were found iopscience.iop.org/0004-637X/773/2/125 $\endgroup$
    – innocent-world
    Sep 13, 2013 at 12:20

3 Answers 3

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Various things:

  • Hawking Radiation: It is theorized that black holes emit a kind of radiation known as Hawking Radiation. We could measure it with the probe, validating the theory.
  • Testing Relativity: General Relativity makes many predictions about space close to a black hole. Accurately testing these predictions will tell us how accurate the theory is (and may also give insight to new physics). Some of the measurable things include:
    • Tidal forces: When near a gravitating object, there are forces which stretch an object in one direction and squeeze it in another. These forces are much stronger near a black hole.
    • Gravitomagnetism/Frame Dragging/Lense-Thirring effect: Rotating gravitational bodies have a tendency to "swirl" space around them, giving rise to gravitomagnetism
    • Electromagnetic properties of a black hole: Reissner–Nordström and Kerr-Newman black holes are charged, and the surface charges have some remarkable and complex properties that mirror the behavior of normal charges on a conductor.
    • Gravitational time dilation: Time behaves strangely near gravitating objects, and extremely strangely near black holes, with large relative differences in the "rate" at which time passes.
  • Figuring out how quasars work: We yet are not very clear on the functioning of quasars. One popular candidate theory is the Blandford-Znajek process, which gives an explanation to how gas jets can arise from rotating black holes with accretion disks, giving rise to quasars. Analyzing the behavior of smaller black holes with accretion disks may help clarify the behavior of quasars for us.
  • Exploratory mission: What if we wanted to build a black hole power plant and attached colony around it?
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    $\begingroup$ There are several wrong statements here. Hawking radiation is much too weak to measure for a solar-mass black hole, and in any case such a black hole would be absorbing radiation faster than it would emitting it. Also, astrophysical black holes are electrically neutral. $\endgroup$
    – user687
    Jul 5, 2017 at 21:43
  • $\begingroup$ Great answer. I wonder if this might be updated after 7 years? There has been a lot of progress in astronomy and physics since then. $\endgroup$
    – Everyday Astronaut
    Aug 25, 2020 at 8:19
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There would be great benefit and could be the objective proof of whether the dominating theories about the nature of a black hole are correct or incorrect.

You can 'prove' any number of things with logic but it doesn't make them necessarily true because you could easily be missing a crucial element of evidence in your deduction/induction. We see this happen all of the time, even though mathematical proofs are logically flawless.

As such, sending a probe in would be able to demonstrate the validity of proofs or lack thereof. If we never hear from it again then we have objective and tangible evidence to weigh in support of the singularity theory, as well as the theory of infinite compression of dimensional matter and space.

For example, you can posit with equations that jumping off your bed will pull you to the floor but you won't know for an absolute certainty until you do it. Theoretically your bed is the only place in the universe where gravity exists.

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  • $\begingroup$ Welcome to space.SE! Maybe a little formatting of your answer will increase its readability. $\endgroup$
    – le_daim
    Jul 5, 2017 at 8:51
  • $\begingroup$ Hi Fezzywig and welcome to the Space StackExchange! I've added some formatting to your response, but you might want to expand your answer with a bit more details on possible competing theories about black holes and how specifically sending a probe to one would be able to prove or disprove aspects of those theories. $\endgroup$
    – Ezra Bailey
    Jul 5, 2017 at 17:12
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It is theorized that Hawking radiation is emitted from black holes. In fact they are believed to eventually evaporate. So hypothetically you could send a signal using Hawking radiation, that could be received outside.

Your more pressing problem (word play:) would be creating a probe that could survive the gravitational and tidal forces of the black hole.

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    $\begingroup$ Hawking radiation is a quantum mechanical process, and cannot be "controlled" from the inside of a black hole. The process occurs outside the black hole using energy "borrowed" from the inside. While it leads to energy loss from the BH, it cannot be used for communication. $\endgroup$
    – Manishearth
    Sep 12, 2013 at 10:57
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    $\begingroup$ A lot of things have been thought impossible over the years; Other then putting the toothpaste back in the tube, most of the impossible things have been accomplished. I find it difficult to believe that the any process capable of removing the vast quantities of material from the interior of a black hole cannot communicate with exterior where the material is transformed into energy. $\endgroup$
    – James Jenkins
    Sep 12, 2013 at 20:47
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    $\begingroup$ There's a difference between a limit imposed by physics and a limit imposed by technological capability or ingenuity. Unless the physics of this changes (it might as well, but if we consider such things then there's not much point in discussing what is possible as everything becomes possible), this stays something that can't be done. $\endgroup$
    – Manishearth
    Sep 12, 2013 at 20:53
  • $\begingroup$ If you want to know why, I suggest you ask on Physics. $\endgroup$
    – Manishearth
    Sep 12, 2013 at 20:56
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    $\begingroup$ @Manishearth, your comment presumes a resolution to the black hole information paradox, which I believe is not a settled issue. If in fact Hawking radiation is unitary, then it may indeed be possible to send information via that channel. $\endgroup$
    – ziggurism
    Feb 17, 2017 at 3:46

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