# Would a black hole interact with light the wavelength of which is greater that the black hole's Schwarzschild radius?

Would it be able to absorb it?

### 4 Answers

- nebLv 75 months ago
Yes, it would interact. A full accurate mathematical description would require a trajectory for the photon. This would be difficult at best since general relativity is only locally ‘simple’ and a wavelength the size of the black hole would require a solution extended over a large region of spacetime.

You really don’t need a quantum gravity for this since you are not at scales that require a quantum gravity.

@ReductioAdAstronomicus is on the right track by assuming a wavelength dependency. All things being equal (and again depending on trajectory) a particle with such a long wavelength would have less probability of interacting with the black hole, but certainly can enter the black hole.

Note an interesting fact that the wavelength of the peak Hawking radiation is about the size of the black hole. This corresponds to incredibly cold temperatures.

- 5 months ago
Very good question. I think you would need a coherent theory of quantum gravity to answer that one.

I'm only guessing (like everyone else, but hey), but I would suggest that the probability of the light being affected would be wavelength dependent. You are basically asking about how the wave function would collapse, and whether that would give a measureable probability of interaction.

I suggest you take your question to a serious physics forum, and see what interesting answers you get.

- MorningfoxLv 75 months ago
It would be a radio wave, not visible light. The smallest BHs are about 10 km radius. I don't see how the BH could absorb the radio wave ... but the accretion disk is much bigger than 10 km, so the radio wave could be absorbed there.

- billrussell42Lv 75 months ago
black holes can absorb light of any wavelength, it's that it can't emit any light.