Singularity is a KSP mod aimed at adding black hole shaders, including gravitational lensing and accretion disk.
Other possible uses include wormholes, stars with gravitational lensing, “white holes” ( a sort of black hole with negative gravity, pushing away light).
This is not a physically correct simulation. The idea is relatively sound, and the force exerted by gravity fades by the square of the distance, but no real physical equations or constants are used.
The shader is based on Pim Schreurs’ Interstellar simulation: https://github.com/sirxemic/Interstellar
Forum thread: https://forum.kerbalspaceprogram.com/index.php?/topic/193709-wip18x-19x-singularity-black-hole-shaders/
Documentation: https://github.com/LGhassen/Singularity/wiki