Regardless of the amount of evidence for the existence of black holes, they remain within the limits of theoretical physics. Because of their properties - structure, lack of emitted light, location and how they work - black holes remain in the shadows. But not all scientists, including Stephen Hawking, believe that traditional black holes must necessarily remain within the framework of modern physics (however, they can have ideal mathematical solutions) - some go further and claim that we should replace them with one of many alternatives.
Some alternatives include gravastars, hybrid wormholes, and quark stars. Last year, two astrophysicists - Carlo Rovelli (University of Toulon, France) and Francesca Vidotto (University of Redbound in the Netherlands) - presented another: a theoretical object called a Planck star (Planck star). It does not replace the standardized black hole model as such, it reimagines it.
A black hole usually has two main components: the event horizon and the singularity itself. The event horizon is quite simple: it is a point, crossing which, nothing can leave the black hole. The Singularity (the heart of a black hole), on the other hand, is much more difficult to understand.
The curvature of space-time at this infinitely dense point becomes infinite. As a result, we cannot logically comprehend what is happening inside the singularity. Even worse: what we arrive at violates several universal rules or laws at once.
The biggest problem has to do with the way the black hole processes information - information that describes the quantum properties of everything that the black hole has swallowed. Physicists say that information cannot - should not - be destroyed, but that seems to be what happens when it is sucked in by the inevitable singularity. This mystery, called the black hole information paradox, is extremely important, but we will return to it later.
What is a Planck star?
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The Planck star relies on what is known as the "big bounce" hypothesis; according to this theory, the universe has adapted to an endless cycle of death and rebirth. In other words, the Big Bang was not necessarily the beginning of everything - just this version of the universe. Before ours, there was another universe: after excessive expansion, it shrank, collapsed and began again (something like reincarnation, only on a cosmic scale).
It is believed that this rebound is preceded by contraction, the opposite of the Big Bang, when the expansion of the universe stops at a certain point - in particular, when the average density of space-time becomes critical. After the collapse begins, all existing matter should collapse into a superdense state (perhaps something similar to a black hole singularity).
The rebound will begin as soon as the matter is compressed to the Planck scale; at least that's what the theory says. Scientists believe that if we reconsider the consequences of a possible large compression, we, in theory, can reconsider the behavior of black holes.
What if, instead of a supernova core collapsing to an infinitely dense point (singularity) - according to our assumption that this is how black holes of stellar mass are formed - this collapse is stopped by "quantum pressure", which looks like "preventing an electron from falling onto the nucleus atom ".
This idea in itself is not so absurd. After all, special pressure - neutron degeneracy - can stop the collapse of a star at a certain mass threshold (leaving neutron stars or pulsars behind), while electron degeneracy performs the same task for stars weighing as much as our Sun.
In addition, the quantum effect that prevents matter from collapsing to infinite density, scientists believe, on a large scale would mean that the rebound “does not occur when the universe reaches Planck size, as previously expected; it occurs when the energy density of matter reaches the Planck density. The universe "bounces" when the energy density of matter reaches the Planck scale, the smallest possible size in physics."
“In other words, quantum gravity may become relevant when the volume of the Universe is 75 orders of magnitude greater than that of Planck,” write the authors of the paper published in the arXiv block.
In search of Planck's star
Of course, if one of these "objects" exists, it will be unimaginably small (even in comparison with an atom), with a diameter of 10 ^ -10 centimeters. And yet it will be 30 orders of magnitude greater than the Planck length (which is 1.61619926 x 10 ^ -35 meters).
As for how the Planck star will look to the observer, and this is really interesting, the factor of time dilation will be especially evident. Time, as it moves, does not go the same for each and every one. It flows differently on the surface of the Earth and in low Earth orbit, although the effect is negligible. The speed at which time ticks should vary dramatically around massive stars and planets, and around black holes.
Before the light crosses the event horizon, it begins to sense the time dilation. We can't be sure about this - we don't even know what's going on inside black holes - but some of the best minds in the world suggest that time almost completely stops there. But you can't see it from the outside.
If this is difficult to understand, and if you've seen the movie Interstellar, remember the episode with the water world. (Spoiler alert). Due to its proximity to Gargantua - a black hole, a wormhole through which the team passed - an hour for people on the planet's surface was equal to tens of years elsewhere. Because of this, and despite the fact that the first human landed on this planet ten years earlier, it is entirely possible that the female astronaut only stayed there for a couple of hours until the second group arrived. Her beacon was active, but no transmissions were received.
Even so: any Planck star can live only a moment before the "rebound": an approximate "length of time that the light needs to overcome it." But for an outside observer, it will live for millions or even billions of years … continuing to exist alongside the black hole itself.
Less problem
At this point, you begin to understand exactly what physicists see in this purely theoretical model. Ultimately it reverts back to the black hole and information paradox. According to scientists, if we replace the singularity with a Planck star, this paradox ceases to be a problem.
They argue that after a time X, black holes, which slowly lose mass over their lifetime due to the gradual emission of Hawking radiation, will eventually collide with the expansion of Planck stars in their cores: at some point, all the information it stores will be released …
What else? Scientists say that Planck stars can "produce a detectable signal, of quantum gravitational origin, with a wavelength of the order of 10-14 cm." In other words, there might be a way to find one, or at least narrow down the search range by looking at certain gamma ray signatures. Perhaps we have already found such a signature, we just do not know about it.
Ilya Khel