Assuming we could get there, and above all survive long enough, what would we see while crossing the event horizon of a supermassive black hole like the one found at the center of the Milky Way? Giving an answer, in the form of a film, is Jeremy Schnittman, astrophysicist at NASA’s Goddard Space Flight Center, who with his team created two simulations exploiting the computing power of the Discover supercomputer supplied to the NASA Center for Climate Simulation. The project required 5 days of computation using 0.3% of the supercomputer’s resources, producing 10 Terabytes of data.
Using Albert Einstein’s General Theory of Relativity as a basis, the best theory available today capable of describing the effects of gravity, Schnittman created two simulations, one relating to an object that crosses the event horizon and hurtles towards the singularity at the center of the black hole, and one instead in the case in which our imaginary video camera manages to escape the gravitational well after having carried out a couple of orbits around the event horizon, which we remember traces the line beyond which the curvature of space-time becomes such that not even a ray of light would escape outside. For the simulation, a non-rotating black hole with a mass equal to 4.3 million times that of the Sun was examined, comparable to Sagittarius A*, the black hole at the center of the Milky Way.
For each of the two scenarios, two films were created, a navigable version that allows the viewer to look at 360 degrees and a “flat” version with explanations in overlays that illustrate what is happening. In both films it is possible to see structures such as the ring of photons, created by the rays of light that are curved by space-time and orbit around the event horizon, and the distortion and multiplication of the image of the celestial vault, always due to the extreme curvature of space-time near a black hole. In the simulation, the event horizon has a diameter of 25 million km and the virtual camera starts at a distance of 640 million km from the event horizon. In real time, it would take about 3 hours before reaching the “edge”, making two orbits around it in 30 minutes each.
If for a passenger on board an astronaut the passage of the event horizon would be instantaneous, for a distant observer the hypothetical spaceship, according to the predictions of General Relativity, would appear to slow down more and more as it approached the event horizon, until it appears completely still as in a snapshot, and then slowly becomes less and less luminous until it disappears completely, as the last photons emitted before crossing the event horizon reach us, sliding further and further into the infrared . From the astronaut’s point of view, once beyond the event horizon, in just over 12 seconds it would be completely “spaghettized” by tidal forces.
