Experiments on a Black Hole Recently it's been theorized that "planet nine" may be a black hole.
If this is the case and we were to fly something out there, what unsolved problems in physics could be answered?
Additionally, if experiments were performed, what would they look like? Do we shine lasers at it? Drop entangled atoms into it?
I asked a similar question on Worldbuilding a few minutes ago which was more sort of 'mission holistic'. Here I'm just interested in the physics that could be done if we got our hands on a black hole, and less about the engineering issues with getting our experiments out to edge of the solar system.
 A: There have been serious suggestions about how to detect a 5-10 earth mass black hole in the outer solar system (as was mentioned in the comments, the horizon would be very small, and thus conventional searches would fail). This recent paper (by Witten!) suggests using hundreds of small spacecraft to probe the gravitational field via timing signals sent to Earth.
But it sounds like you’re less interested in experiments to detect such a black hole (BH), and more in experiments we could do with such a BH to test, for instance, quantum gravity or quantum effects of the horizon. Most people believe that semiclassical gravity (quantum fields in a curved background) works well to describe physics as you cross the horizon, and you really need to approach Planck scale regimes in the deep interior before you start probing quantum gravity.
As for horizon physics, since the lifetime of a $10 M_\oplus$ BH is longer than the age of the universe (over $10^{50}$ years) and the temperature of the horizon will be less than that of the cosmic microwave background ($10^{-3}$ K vs $2.7$ K for the CMB)*, it will be very hard to observe Hawking radiation or watch the BH evaporate (let alone try and perform something like the Hayden-Preskill experiment where we test black hole information loss by collecting Hawking radiation for the duration of the BH’s lifetime, or try and observe the effect of backreaction on the horizon a la a Dray-’t Hooft shockwave).
Realistically, the types of experiments you could do would be tests of GR in high curvature regimes, but it’s certainly possible there are more creative experiments to test quantum properties of the horizon.
*Technically, as the ambient temperature is higher than the horizon temperature, the BH would not be evaporating but instead would be absorbing energy.
