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What's the physics behind the accretion disk and its look? I would have expected black holes to look more like the last few images where it's just a black hole distorting light around it. Is it just pure eye candy, or do black holes actually output a significant amount of light outside their event horizons?

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My take on the accretion disk isn't very physically-based. It's really mostly meant as eye candy. However, the distortion (the form it takes) is physical and due to the Schwarzschild geometry.

The physical explanation of an accretion disk would be some matter that is orbiting the black hole and emitting radiation, so it makes some sense at least. https://en.wikipedia.org/wiki/Accretion_disk

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