I wanted two characters unaffected by the heat and gravity to be close to a super massive black hole within the accretion disk, at times moving in orbit and at times completely still.

Stars and planets will be engulfed by the black hole.

Would it just be blindlingly white light or will the two viewers see something different? (I could change the frequency of light they are able to see if it creates a more impressive image.)

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    $\begingroup$ This question needs substantial further detail before it can be meaningfully answered. What an accretion disc looks like is dependent on what is in it. If it's just cosmic dust and gases being drawn in, there isn't going to be much to see. If planets are being engulfed, that's a different story. If stars are being torn apart, that's yet another. $\endgroup$ – jdunlop Feb 5 at 18:30
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    $\begingroup$ @ragharan You'll want to specify the mass of the black hole, too. If it's Sagittarius A*-sized, it's about 8.6 x 10^36 kg. A complete answer should probably involve Gravitational Lensing somehow; that's what caused the effect in the image I linked to on the other question. $\endgroup$ – Ray Feb 5 at 18:45
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    $\begingroup$ It also matters if the accretion disc forms a quasar. In that case, the accretion disc itself becomes dense enough to form a layer around the black hole that performs fusion which basically means it's like being in a supermassive star with a diameter in excess of 1 light-year $\endgroup$ – Nosajimiki Feb 5 at 18:51
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    $\begingroup$ @ragharan I refer you to my answer to your previous question: worldbuilding.stackexchange.com/questions/138503/… $\endgroup$ – Agrajag Feb 5 at 20:02
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    $\begingroup$ "Stars and planets will be engulfed" isn't really sufficient either - bear in mind that even with black holes, we're dealing with astronomical time scales. Stars can't cross enormous voids to be swallowed by a black hole in years or even centuries. What is currently being eaten by the hole? If a star has wandered in, is it dying or are its remains entirely in the disc? All of these things change the appearance of the hole. It could very easily just have a whispy-thin gaseous disc, hundreds of lightyears from any other masses - in which case, it wouldn't look like anything at all. $\endgroup$ – jdunlop Feb 5 at 21:32

Firstly, your characters also need to be immune to the exotic array of radiation that an active Accretion disc outputs.

Secondly, no they do not see a uniform disc. An accretion disc that is hot enough to be interesting also has a significant redshift on the part of the disc moving away from you (material is moving at a fair fraction of the speed of light)

Thirdly, there are a range of echo images created by a rotating black hole on the 'approaching' side of the disc due to gravitational lensing. These show distorted blue-shifted images of the opposite side of the disc, highly-stretched parallel to the rotation axis of the disc.

EDIT as per Thucydides suggestion: Here is a visualisation of a black hole from the film Interstellar using Kip Thorne's Kerr metric formalisation. The first is that actually used in the film. It is somewhat inaccurate for the sake of looking visually pleasing/simple. The next two images are increasingly realistic for moderate rotation speeds; they show redshift and a more realistic messy accretion disc.

Lots of debate to be had about the exact details of these images for storytelling guidance (your view of a black hole changes a LOT as you move relative to it), but they are a good starting point enter image description here

  • $\begingroup$ The image Kip Thorn came up with for the movie "Interstellar" is a good starting point. $\endgroup$ – Thucydides Feb 14 at 16:55
  • $\begingroup$ Good point. It's an accurate representation of a non-spinning black hole. (I get a wee bit grumpy about interstellar as a sci fi piece though...) $\endgroup$ – Mark_Anderson Feb 14 at 18:34
  • $\begingroup$ Interstellar as a movie seems to have bits of about three different not fully developed stories crammed into the script. The visuals are quite stunning, however. $\endgroup$ – Thucydides Feb 15 at 15:21

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