Black holes are areas in space with extremely strong gravity that can trap everything, including light.
One supermassive black hole is found in the center of the Milky Way galaxy.
Observing a black hole requires a spaceship and a spacesuit. The disk of matter around the black hole emits intense radiation and light that is dangerous without proper protection.
Inside a black hole, time and space behave differently, and objects are disconnected from the outside.
Black holes are areas in space with intense gravity that capture everything, including light.
A supermassive black hole named Sagittarius A* is in the center of the Milky Way galaxy.
Observing a black hole requires a spaceship and a spacesuit to protect from intense radiation and light.
Approaching the black hole, the disk of matter around it emits intense blue light and appears warped due to strong gravity.
Inside a black hole, space-time is curved, and objects are disconnected from the outside.
Crossing the horizon of a black hole means that signals can no longer reach outside.
Falling into a black hole would cause spaghettification, where our body is stretched until it tears apart.
The difference in pull between our feet and head would cause our body to quickly tear apart.
A circle of light would intensify around us as we reach the center of the black hole.
Modern physics cannot accurately explain what happens close to the center of a black hole.
It is being questioned whether one could survive crossing the horizon.
Our current theories can give us an idea of what we might see, but there are still many mysteries left to solve.
The disk appears extremely bright at first, and we can't distinguish anything.
We imagine that our helmet has a visor that helps reduce the brightness of the disk so that we can observe it in detail and see the stars in the background.
The disk emits more blue within the electromagnetic spectrum produced, and the visor filters everything but visible light that our eyes can see.
The disc is blue because this color is more energetic.
One side of the disk looks brighter than the other because of the doppler effect.
The back of the disc appears warped as if it were folded around the horizon, forming a ring of light, due to the strong gravity of the black hole, which deflects light rays, acting like a gravitational lens.
Looking in one direction, we observe objects that are actually located elsewhere.
Finally, the stars in the background seem ever so slightly blue.
The doppler effect occurs when matter orbits very quickly, such that on one side, it approaches us at high speed, while on the other side, it moves away.
On one side, the light waves get stacked together, and we receive them with greater frequency, while on the other side, light gets stretched, and we receive it with less energy.
When falling towards the black hole, we catch up with the light in front of us, while the light behind us has more difficulty reaching us.
As we approach the black hole, the passengers in the spaceship see our image fade gradually and slow down until freezing on the horizon.
The light that we emit takes more and more time to escape the black hole, is received increasingly slowly and gradually fades away.
The passengers will never see us cross the horizon.
Just 24 seconds after crossing the photon sphere, it is time to reach the horizon.
After this moment, it will be impossible for us to go back.
It would be difficult to determine when exactly we crossed the horizon.
We still receive the light of distant stars which falls with us.
We can still see the spaceship in orbit in which the clock, even if it seems slowed down, is still ticking.
We can still perfectly see our body and, in particular, our feet because even if all light is carried inwards, it can still move upwards relative to us and thus reach our eyes.
On a global scale, space-time is curved by the black hole, and generates this horizon inside which objects are disconnected from the outside.
At the local scale, space-time is almost flat, and the curvature is not noticeable, which means that everything behaves normally.
Modern physics cannot describe what happens this close to the center of a black hole.
Our current theories describe singularities - points where the curvature of space-time becomes infinite.
Scientists suspect that these singularities do not really exist.
We would have to unify gravity with quantum physics if we wish to understand these extreme regions of the cosmos.
For now, some hypotheses even question the fact that one could survive crossing the horizon.
Moreover, in reality, black holes can have an angular momentum that generates strange effects with multiple horizons and mathematical instabilities whose consequences we do not yet understand.
That said, our current theory still gives us a good idea of what we would see.
There are, however, many mysteries left to solve, and we will have to wait until our theories are perfected to understand what truly happens at the heart of a real black hole.