Black holes should have accretion disks from which matter falls into them, and after crossing the event horizon, matter should no longer have a way to get out. Could something affect this order of things?
Once you hit the event horizon of a black hole, you can't get out. There is no such speed that would help get out of there, even the speed of light is not enough for this. But, according to general relativity, space bends in the presence of mass and energy, and the merging of black holes is one of the most extreme scenarios in nature. Is it possible to fall into a black hole, cross the event horizon, and then escape from there while this horizon is distorted as a result of a massive merger? This question arose from our reader:
The idea, of course, is crazy. But is she crazy enough to work? Let's find out.
When the lifetime of a massive star comes to an end, or when sufficiently massive remnants of stars merge, the result may be a BH. The event horizon will be proportional to its mass, and around it there will be an accretion disk of matter falling into it.
Usually, a BH is formed when the core of a massive star collapses, which occurs either after a supernova explosion, or when neutron stars merge, or during direct collapse. As far as we know, each BH is made up of matter that was previously part of a star, so a BH in many ways is the final form of stellar remnants. Some BHs appear in isolation, while others are part of a binary system or even a system of several stars. Over time, BHs can not only approach in a spiral and merge, but also absorb other matter falling into the event horizon.
In the case of a Schwarzschild BH, falling into it leads to singularity and darkness. It doesn't matter in which direction you move, how much you accelerate, and so on - crossing the horizon will inevitably lead to a meeting with a singularity.
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When something crosses the BH event horizon from the outside, that matter is doomed. In just a few seconds, it will inevitably encounter a singularity at the center of the BH: in the case of a non-rotating BH, it will be a point, and in the case of a rotating BH, it will be a ring. The BH itself has no memory of which particles fell into it, and what their quantum state was. From the point of view of information, only the total mass, charge and angular momentum of the BH remain.
In the last moments before the merger, space-time around a pair of BHs will be distorted, and matter will continue to fall into both BHs from the space surrounding them. There is not a single moment in which there could be an opportunity to escape from the inside of the event horizon to the outside.
Then one can imagine a situation when matter falls into a BH at the last stages of merging, when a BH is ready to merge with another. Since BHs, in theory, should always have accretion disks, and in interstellar space there is always matter flying somewhere, the particles must constantly cross the event horizon. Everything is clear here, and we can consider a particle that has just entered the event horizon, in the last moments before the merger.
Can she run away? Can she "jump" from one BH to another? Let's examine the situation in terms of space-time.
Computer simulation of the merger of two black holes and the space-time distorted by them. Gravitational waves are emitted in abundance, but matter must not escape.
When two BHs merge, the merger itself occurs after a long period of approach in a spiral, during which energy is radiated outward in the form of gravitational waves. It is emitted until the very last moment before the merger. But because of this, the event horizons of both BHs are not compressed; this energy appears due to the ever increasing deformation of space-time in the area of the center of mass. One can imagine a similar process in which the energy of the planet Mercury would be lost - as a result, the planet would approach the Sun, but this would not change the properties of the Sun and Mercury.
However, at the very last moments before the merger of the BH, the event horizons begin to distort due to their gravitational influence on each other. Fortunately, the numerical scientists of the theory of relativity have already calculated exactly how this merger affects the event horizons, and this is an amazingly informative calculation.
Despite the fact that up to 5% of the total mass of a BH before merging can escape outward in the form of gravitational waves, it can be noted that event horizons never contract; a connection appears between them, they are slightly distorted, and then increase in volume. The last point is important: if we take two BHs of the same mass, their event horizons will occupy a certain volume. If we merge them and create one BH of double mass, then the volume occupied by the event horizon will be four times larger than the total volume that the event horizons of two BHs occupied. The mass of the BH is directly proportional to its radius, and the volume is proportional to the cube of the radius.
We have found many BHs, and for all of them, the radius of the event horizon is directly proportional to the mass. Double the mass, the radius doubles, the horizon's surface area quadruples, and the volume quadruples!
It turns out that even if you keep a particle stationary inside the BH, and make it fall as slowly as possible to the singularity in the center, it will still not be able to get out of the event horizon. The total volume of the total event horizon is increasing, not decreasing, and regardless of the trajectory of a particle crossing the event horizon, it is destined to be forever swallowed by the combined singularity of both BHs.
In many collision scenarios in astrophysics, there is a "blowout" when matter from inside an object is ejected outward during a cataclysm. But in the case of BH merging, everything that was inside remains inside; most of what was outside goes inside; only a small part of what was outside can, in principle, escape. If something has fallen inside, it is doomed, and nothing will change it, no matter what you throw into the BH - even another BH!