A new video simulation, created with the supercomputer Discover of NASA, shows us in an extremely detailed and scientifically accurate way what we would see during a hypothetical journey towards a supermassive black hole, penetrating through its accretion disk and its event horizon, i.e. the “no return” boundary beyond which it is impossible to get out of the black hole, all the way inside the event horizon. The incredible detail of the simulation was achieved thanks to Discover's 129,000 processors and the skilled hands of Jeremy Schnittman And Brian Powell of the Goddard Space Flight Center. In this case, two different scenarios of a “flight” around a supermassive black hole with a mass approximately 4.3 million times that of the Sun were reproduced, similar to Sagittarius A*, the black hole at the center of the Milky Way of which we recently obtained a first image. In the first scenario, the “camera” falls beyond the event horizon, while in the second it simply touches it and then moves away.
In both cases, what appears to us first is the accretion disk around the black hole, i.e. the material orbiting around the black hole at such speeds as to heat up and emit light, which thus loses energy and is “swallowed” by the event horizon. This disk is what we see shining in the famous images of black holes recently released by the Event Horizon Telescope project (specifically M87* and Sagittarius A*), and it appears deformed, even “bent” by the enormous gravity of the black hole. The material orbiting in the disk is moving towards or away from us in various areas of the disk depending on its direction of rotation. Due to an effect of Albert Einstein's relativity, the light emitted by the disk will appear more or less intense in the regions that rotate towards us or in the opposite direction. The so-called photon rings, composed of photons (i.e. particles of light) that are orbiting around the black hole due to the extreme curvature of spacetime in those regions. Proceeding towards the event horizon, these rings become increasingly thinner, as the number of orbits traveled by the photons to arrive so close to its surface increases.
And here we are finally at the event horizon. The choice of a supermassive black hole is not random: a smaller and lower mass black hole, like black holes of stellar origin, would determine much more intense tidal forces, which would disintegrate any camera well before reaching the event horizon . Again due to the effect of relativity, in this phase the time perceived by the camera increasingly deviates from the time of the observer: the camera takes about three hours to fall on the event horizon, but the time dilation given by gravity implies that in reality a hypothetical observer on Earth would see it slow down so much that it would never reach the event horizon. Once this surface has been overcome, gravity is so intense that it permanently traps everything that has been attracted inside, including electromagnetic waves, and therefore light, creating a region from which it is impossible to communicate with the outside. The camera can therefore no longer send the images it is shooting to Earth, but continues to be reached by light coming from outside for a few seconds, before finally being destroyed by the force of gravity.
