Research · Research notes
Disc temperature and colour
BlackHoles.fyi draws real black holes from the physics of light and gas near them. These are our working notes on one part of that picture: what we found while drawing it, and where the research is still unclear.
The gas round a black hole glows because it is hot, and how hot each ring of it is sets its colour. The site works the temperature out from a published model of a thin disc (Novikov and Thorne), for each hole's own mass and feeding rate, and turns it into a colour as a hot object of that temperature would look. The disc's colour changes again as its gas moves towards or away from the camera, which is doppler beaming on a black hole's disc.
The temperature of each ring of gas comes from the Novikov and Thorne model, worked out for each hole's own mass and how fast it feeds. To turn a temperature into a colour, the site adds up how strongly an object at that temperature glows at 14 wavelengths across the colours the eye can see, then turns that into the red, green and blue a screen shows.
The disc's look changed a good deal in early November 2026. An earlier version drew the disc a warm gold, as gas at about 4 800 K would look.
Updated 8 November 2026
The papers behind it
- Shakura and Sunyaev 1973, Black holes in binary systems: observational appearance, A&A 24, 337
- Novikov and Thorne 1973, Astrophysics of black holes, in Black Holes (Les Houches lectures)
- Page and Thorne 1974, Disk-accretion onto a black hole, ApJ 191, 499