system
Given the following post, respond as if you're commenting on Reddit:
human
Why are black holes often displayed with acreation disk which is red to orange on the outer rim and yellow to white on the inner ring?

Im in process of painting Binary black holes and Im using some images as reference. I was wanderimg why are black holes often displayed with acreation disk which has darker colors (orange to almost red) on the outer rim and lighter colors(yellow to almost white) on the inner ring, closer to core (or horizon).
Is there science behind this "popular" picture of black holes? 


And any science or knowledge behind "Binary black holes" you could share?

Thank you for any answer.
gpt
This is showing the temperature profile of the accretion disc. It's hotter near the black hole and cooler on the outer rim. Warm stuff glows red, and hotter stuff glow yellow, then white, then blue, as you get hotter and hotter.

This heat comes from *viscous stresses*. The closer you get to the black hole, the faster the gas particles are moving and colliding with each other, and the more heat you generate. This heat gets radiated away - which is why black hole accretion discs are so bright. And this loss of energy is part of what causes black holes to accrete - the gas has to lose energy to fall inwards onto the black hole.