Once an object enters a black hole, it can no longer leave it. No matter how much energy you have, you can never move faster than the speed of light and cross the event horizon from within. But what if you try to fool this little rule and plunge a tiny object into the event horizon, tying it to a more massive one that can leave the horizon? Is it possible to get something out of a black hole somehow? The laws of physics are strict, but they must answer the question, is it possible or not. Ethan Siegel of Medium.com suggests we find out.
A black hole is not just a superdense and supermassive singularity in which space is curved so much that everything that gets inside can no longer get out. Though what we usually think of is a black hole - to be exact - a region of space around these objects from which no form of matter or energy - and not even light itself - can escape. This is not as exotic as one might think. If you take the Sun as it is, and squeeze it to a radius of several kilometers, you get almost a black hole. And although our Sun is not threatened with such a transition, there are stars in the Universe that leave behind these mysterious objects.
The most massive stars in the universe - stars of twenty, forty, one hundred, or even 260 solar masses - are the bluest, hottest, and brightest objects. They also burn out nuclear fuel in their depths faster than other stars: in one or two million years instead of many billions, like the Sun. When these inner cores run out of nuclear fuel, they become hostages of the most powerful gravitational forces: so powerful that in the absence without the incredible pressure of nuclear fusion that they are opposed to, they simply collapse. At best, nuclei and electrons gain so much energy that they merge into a mass of neurons connected together. If this core is more massive than a few suns, these neutrons will be dense and massive enough to collapse into a black hole.
So, remember, the minimum mass for a black hole is several solar masses. Black holes can grow from much larger masses, merging together, devouring matter and energy and seeping into the centers of galaxies. An object was found in the center of the Milky Way that is four million times the mass of the Sun. Individual stars can be identified in its orbit, but no light of any wavelength is emitted.
Other galaxies have even more massive black holes, whose masses are thousands of times larger than our own, and there is no theoretical upper limit on their height. But there are two interesting properties of black holes that can lead us to the answer to the question asked at the very beginning: is it possible to pull something "on a leash"? The first property relates to what happens to space as the black hole grows. The principle of a black hole is such that no object can escape from its gravitational attraction in the region of space, no matter how accelerated, even moving at the speed of light. The boundary between where an object can leave the black hole and where it cannot is called the event horizon. Every black hole has it.
Surprisingly, the curvature of space is much less on the event horizon near the most massive black holes and increases in less massive ones. Think about this: If you were to "stand" on the event horizon with your right foot on the edge and your head back 1.6 meters from the singularity, force would stretch your body - a process called spaghettification. If this black hole were the same as at the center of our galaxy, the tensile force would be only 0.1% of the gravitational force on Earth, whereas if the Earth itself turned into a black hole, and you were standing on it, the tensile force would be 1020 times the earth's gravity.
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If these tensile forces are small at the edge of the event horizon, they will not be much larger inside the event horizon, which means - given the electromagnetic forces that hold solid objects together - perhaps we could do our thing: plunge the object into the event horizon and almost immediately take out. Can you do this? To understand, let's look at what happens at the very border between a neutron star and a black hole.
Imagine you have an extremely dense ball of neutrons, but a photon on its surface can still escape into space and not necessarily return to a neutron star. Now let's place another neuron on the surface. Suddenly the core can no longer resist gravitational collapse. But instead of thinking about what is happening on the surface, let's think about what is happening inside, where the black hole is forming. Imagine a single neutron made up of quarks and gluons, and imagine how gluons need to move from one quark to another in the neutron for the exchange of forces to take place.
Now one of these quarks is closer to the singularity at the center of the black hole, and the other is farther away. For the exchange of forces to take place - and for the neutron to be stable - the gluon at a certain moment must pass from the near quark to the far one. But this is impossible even at the speed of light (and gluons have no mass). All null geodesics, or the path of an object moving at the speed of light, will result in a singularity at the center of the black hole. Moreover, they will never go further from the black hole singularity than at the moment of ejection. This is why the neutron inside the black hole's event horizon must collapse and become part of the singularity at the center.
So let's go back to the harness example: you took a small mass, tied it to a larger vessel; the ship is out of the event horizon and the mass is submerged. When any particle crosses the event horizon, it cannot leave it again - not a particle, not even light. But photons and gluons remain the very particles that we need to exchange forces between particles that are outside the event horizon, and they also cannot go anywhere.
This does not necessarily mean that the cable will break; rather, the singularity will drag on the entire ship. Of course, tidal forces under certain conditions will not tear you apart, but the achievement of the singularity will be inevitable. The incredible gravity and the fact that all particles of all masses, energies and velocities will have no choice but to travel to the singularity is what will take place.
Therefore, unfortunately, they have not yet found a way out of the black hole after crossing the event horizon. You can reduce losses and cut off what has already got inside, or stay in touch and drown. The choice is up to you.
Ilya Khel