This is the art of maths, using mathematics to create a wonderful visual graphic. The most common for of this is fractals. The most famous was the Mandlebrot fractal using a formula of Z=Z2+c. If after so many calculations the number has stayed within a specified 2D space it is assumed that this will be here for infinity so is a black hole. If however it escapes then the number of times the calculation has been processed before it escaped is mapped to a colour and displayed like so.