> I thought "oooh this is interesting I wonder how they are going to do physically accurate on an end device" Recalling how the original particle sim was something like 100TB, took 2 weeks to generate and seemed to write in a way that killed disks. but that was >10 years ago, so what clever stuff has been done to model it locally.

Yes, totally reasonable question! Those terabytes surely were things like fluid/matter motion around the black hole, stuff like this.

Here, I definitely don't simulate matter motion around the black hole as a particle/fluid sim does – instead, I focus on simulating the effects of the black hole itself. Matter distribution and motion (where it is used at all, ie not in camera mode) is described by simple functions phenomenologically.

The single most notable effect of a black hole is strong light bending (+ time delays), and it is properly simulated in all modes in this app. Next, relativistic beaming (Doppler boosting) and gravitational redshift are simulated for the accretion disk emission as well. If you zoom out, the jet is visible as well – it's relatively far away, so it is rendered with special relativity only; ie, no GR, but full volumetric rendering taking all SR effects into account. Admittedly, the GR-SR seam implementation can be improved somewhat.