Comment by aplavin
16 hours ago
One side of the accretion disk is indeed brighter than the other – in the default view in the app, the bottom part is brighter. The effect appears quite clearly visible to me, although the exact contrast depends on the colorscale mapping. Here, I tried to find a colorscale that works well for both the disk and the jet, which naturally means the leading/trailing edge contrast can be less than in the linear mapping. Hope it explains the visual effect!
Kerr vs Schwarzschild (static vs rotating black holes) is a much smaller effect visually – that's why it is so hard for us to measure black hole spins (= how fast they are rotating) observationally, even with the Event Horizon Telescope.
I think the contrast between the two sides is typically greater with an optically thick disk, and it looks like you are rendering an optically thin disk. I think that's the main difference from what I was expecting when I saw it.
Very cool demo! Thanks for sharing!
(For reference, my experience rendering black holes is recreating Luminet's rendering from the late 70s: https://www.ioccc.org/2025/cesmoak/index.html )
True, the disk is rendered optically (and geometrically) thin. This is done so that real-time performance is attained on devices like phones – volumetric GR rendering would be significantly more expensive. The jet (zoom out to see it) is rendered with full volumetric effects, because it's just special relativity there.
Fortran punchcard style to render black holes?! That's really going full circle to the origins, I really enjoyed reading about Luminet's work some time ago.
Oh nice, I had not zoomed out enough. I don't think I've seen the relativistic jets rendered before. The AR mode looks great on my phone.
Yep, I had fun learning a lot about punchcards, Fortran, and the math behind black holes. I suspect I'm doing something similar to you in my Fortran implementation, raymarching along the null geodesic to come up with my final image: https://imgur.com/a/czysDls
Also, I have to point out the "going full circle" pun, intended or not.
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