How does it feel to fall into a spinning black hole? It is impossible to observe this, but you can calculate … The question is extremely interesting, and science is able to answer it, because the properties of black holes are known, writes Forbes. The doctor of astrophysics spoke with many people who made such calculations, and is in a hurry to talk about the extremely interesting findings, supported by a number of visualizations.
There are many terrible ways in which the universe can destroy something. In space, if you try to hold your breath, your lungs will explode. And if you exhale all the air down to the last molecule, then after a couple of seconds, switch off. In some places in the universe, you will turn into ice when the heat leaves your body; in other places it is so hot that your atoms will turn into plasma. But when I consider how the universe can get rid of me (or you), I cannot imagine a more mesmerizing sight than going into a black hole. Scientist Heino Falcke, who is working on the Event Horizon Telescope project, is of the same opinion. He's asking:
How does it feel to fall into a spinning black hole? It is impossible to observe this, but it is possible to calculate … I have talked with many people who have made such calculations, but I am getting old and beginning to forget a lot.
This question is extremely interesting, and science is able to answer it. Let's ask her.
According to our theory of gravitation, Einstein's general theory of relativity, there are only three characteristics that determine the properties of a black hole. Here they are:
1. Mass, or the total amount of matter and the corresponding amount of energy (calculated by the formula E = mc2), which was spent on the formation and growth of the black hole in its current state.
2. The charge, or the total electric charge arising in a black hole from all positively and negatively charged objects that fall there during its existence.
3. The angular momentum, or rotational moment, which measures the total amount of rotational motion of a black hole.
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Realistically, all black holes in the Universe must have a large mass, significant torque and negligible charge. This complicates things very much.
Thinking about a black hole, we represent it in a simplified form, characterizing only by mass. It has an event horizon around a single point (singularity), as well as an area surrounding this point, from which light cannot escape. This area has the shape of a perfect sphere and a boundary separating areas that can emit light and those that do not. This border is the event horizon. The event horizon is located at a very specific and equal distance (Schwarzschild radius) from the singularity in all directions.
This is a simplified description of a real black hole. But it is better to start with physical phenomena occurring in two specific locations: outside the event horizon and inside the event horizon.
Beyond the event horizon, gravity behaves as usual. Space is curved by the presence of this mass, giving all objects in the universe an acceleration in the direction of the central singularity. If we start at a great distance from the resting black hole and let the object fall into it, what do we see?
Suppose we are able to remain still. In this case, we will see how the object is slowly but with acceleration moving away from us, moving towards this black hole. It accelerates towards the event horizon while retaining its color. But then something strange happens. The object seems to slow down, fade out and blur, and then becomes more and more red. But it does not completely disappear. Instead, it seems to be approaching this state of disappearance: it becomes less distinct, more red, and it is more and more difficult to detect it. The event horizon is like the asymptote of the light of an object: we can always see it if we look closely.
Now imagine the same scenario, but this time we will not observe an object falling into a black hole from afar. We will imagine ourselves in the place of a falling object. And in this case, our sensations will be completely different.
The event horizon grows much faster as space warps than we expected. Space is so curved around the event horizon that we begin to see numerous images of the outward universe, as if it were being reflected and turned inside out.
And when we cross the event horizon and get inside, we see not only the outer universe, but part of it inside the event horizon. The light we receive shifts to the violet part of the spectrum, then back to the red, and we inevitably fall into the singularity. In the last moments, outer space seems strangely flat.
The physical picture of this phenomenon is complex, but the calculations are quite simple and straightforward, and they were brilliantly performed in a series of scientific papers written in 2000-2010 by Andrew Hamilton of the University of Colorado. Hamilton also created a series of vivid visualizations of what we see when we fall into a black hole based on his calculations.
There are many lessons to be learned from these results, and many of them are counter-intuitive. Trying to figure them out will help us change our visual perceptions of space. Usually we imagine space as some kind of motionless structure and think that the observer has fallen somewhere inside it. However, within the event horizon, we are constantly on the move. All space is essentially in motion like a conveyor belt. It moves constantly, moving everything within itself in the direction of the singularity.
It moves everything so fast that even if we start to accelerate away from the singularity, having an infinite amount of force, we will still fall towards the center. Light from objects outside the event horizon will still reach us from all directions, but we, being inside the event horizon, will be able to see only a part of these objects.
The line that defines the boundary between what the observer sees is called cardiodide in mathematics. The component of the largest radius of the cardioid touches the event horizon, and the component of the smallest radius ends at the singularity. This means that although the singularity is a point, it does not inevitably connect what goes in with everything else. If you and I go simultaneously to opposite sides of the event horizon, then after crossing it, we will no longer be able to see each other.
The reason for this is in the structure of the Universe itself, which is constantly in motion. Inside the event horizon, space travels faster than light, and therefore nothing can go beyond the black hole. For the same reason, while inside a black hole, we begin to see strange things, for example, many images of the same object.
You can understand this by asking the following question: "Where is the singularity?"
Being inside the event horizon of a black hole, we, having started moving in any direction, will eventually bury ourselves in a singularity. It's amazing, but the singularity appears in all directions! If you move your feet forward and accelerate, you will see your feet below you and above you at the same time. All this is quite easy to calculate, although such a picture seems to be a striking paradox. Meanwhile, we are considering only a simplified case: a black hole that does not rotate.
The first photograph of a black hole and its fiery halo.
Now let's get down to the funniest thing in terms of physics and look at a black hole that is spinning. Black holes owe their origin to systems of matter, such as stars, which constantly rotate at one speed or another. In our Universe (and in general relativity), the torque is a conserved property of any closed system, and there is no way to get rid of it. When the aggregate of matter shrinks to a radius that is less than the radius of the event horizon, the rotational moment, like mass, is trapped and trapped inside.
The solution is much more complicated here. Einstein put forward his theory of relativity in 1915, and Karl Schwarzschild got the solution for a non-rotating black hole in early 1916, that is, a couple of months later. But the next step in realistic modeling of this problem - given that a black hole has not only mass but also torque - was taken only in 1963 by Roy Kerr, who found a solution.
There are some fundamental and important differences between Schwarzschild's somewhat naive and simple solution, and Kerr's more realistic and complex solution. Here are some surprising differences:
1. Instead of a single solution to the question of where the event horizon is, a rotating black hole has two mathematical solutions: an inner and outer event horizon.
2. Beyond the outer event horizon, there is a place known as the ergosphere, where space itself moves at an angular velocity equal to the speed of light, and particles that enter it receive colossal acceleration.
3. There is a maximum allowable torque / mass ratio. If the value of the torque is too large, the black hole emits this energy (through gravitational radiation) until the ratio returns to normal.
4. And the most striking thing is that the singularity at the center of the black hole is no longer a point, but rather a one-dimensional ring, where the radius of the ring is determined by the mass and rotational moment of the black hole.
Knowing all this, can we understand what happens when we get inside a rotating black hole? Yes, the same as entering a non-rotating black hole, except that space does not behave as if it is falling into a central singularity. The space behaves as if it is being pulled around the circumference in the direction of rotation. It looks like a whirlpool. The greater the ratio of rotational motion to mass, the faster the rotation occurs.
This means that if we see something falling inward, we will notice how this something turns red and gradually disappears, but not only. It is compressed and turns into a ring or disc in the direction of rotation. If we get inside, we will be circled like on a mad carousel, sucked into the center. And when we reach the singularity, it will be in the form of a ring. Different parts of our body will fall into a singularity on the inner ergosurface of the Kerr black hole in different spatial coordinates. As we approach the singularity from within the event horizon, we will gradually lose the ability to see other parts of our body.
The most important information to be drawn from all this is that the structure of space itself is in motion; and the event horizon is defined as the place where you, even with the ability to travel at the limit of the highest cosmic speed, which is the speed of light, and in any direction, will always stumble upon a singularity.
Andrew Hamilton's renderings are the best and most scientifically accurate simulations of what happens when you hit a black hole. They are so counterintuitive and so paradoxical that I can only recommend you one thing: watch them over and over again until you fool yourself into thinking you understand them. This is a wonderful and fantastic sight. And if the spirit of adventurism in you is so strong that you decide to go into a black hole and get inside the event horizon, this will be the last thing you see!
Ethan Siegel