Real-Time Black Hole

This is a physically accurate visualization of a black hole, made in Unity. The greatest part is, it is real-time! No ray-tracing, all implemented in a shader graph. Even on low-end hardware, this will run on much more than 60 frames per second. Modern hardware spits this out at hundreds of frames per second without breaking a sweat! A lot of physics goes into the look of a black hole, and despite the low computational cost, most of it is captured by this visualization:

• Bending of background light: background light passing by the black hole will be bent. This distorts the background behind the black hole in a very specific way.
• Bending of light from the accretion disk: light emitted by the accretion disk will also be bent, but since that light is emitted close to the black hole, it is bent slightly less, depending on where it is emitted.
• Temperature of the accretion disk: the light emitted by the accretion disk is determined by the temperature of the gas at each location in the disk. This type of radiation is called blackbody radiation, and has a specific color and brightness depending on the temperature. By describing the temperature at every position in the accretion disk in a realistic way, we get a realistic color!
• Relativistic Doppler shift: gas in the accretion disk rotates around the black hole. Gas close to the black hole orbits faster than gas further away. In accretion disks around black holes, gas rotates very fast. Due to this speed, gas moving towards the camera looks brighter and bluer (this is referred to as "blueshift"), while gas moving away from the camera looks dimmer and redder (referred to as "redshift"). This is called the relativistic Doppler shift; it's exactly like how sound sounds higher pitched when the source is moving towards you, but then for light waves instead of sound waves!
• Clumps in the disk: an accretion disk is never entirely smooth, there are clumps of higher density and cavities of lower density. As a bonus, including this "clumpiness" also shows the rotation of the disk more clearly!
• Gravitational Doppler shift: just like a high speed blueshifts or redshifts light, so too does the presence of a strong gravitational field. Light emitted close to the black hole is redshifted, appearing redder and dimmer.

Unfortunately, some physical effects were not possible to be implemented in this visualization:

• Rotation of the black hole: this visualization is for a non-rotating black hole. A rotating black hole bends light in a different way. Because of the way this visualization is implemented – making use of symmetries in the way the (non-rotating) black hole bends light – it was not possible to include this.
• Gravitational blueshift of background light: for the same reason light emitted close to the black hole is redshifted, background light seen by a camera close to the black hole is blueshifted. In this visualization, the background light is described by an image. An image contains 3 colors: red green and blue. These colors obviously describe the visible light. However, when the camera is close to the black hole, the background light is blueshifted so much that visible light becomes invisible, and infrared light becomes visible. The problem, of course, is that the image does not contain any information on infrared light. For this reason I decided to not include the gravitational blueshift of background light at all.
• Relativistic jets: an accretion disk around a black hole produces two jets perpendicular to the disk. These jets carry away incredibly hot gas, at extreme speeds: up to 99% of the speed of light. These jets are a key feature of black holes with accretion disks, but once again, because of the way this visualization is implemented, it was not possible to include them.

I have a 7-part series of videos on my YouTube channel on how I made this: watch it here!