Tuesday, 2 February 2021

Dark matter and energy fell into a black hole. It is possible that in fact, no dark matter and energy in their usual representation exists.

Dark matter and energy fell into a black hole.

Dark matter and energy fell into a black hole. 

A recently published study by Russian physicists forces a completely new look at the origin and nature of dark matter and dark energy. The model of dark matter from unknown particles, as well as dark energy of an obscure nature, is too deeply rooted in the minds of many researchers. But if the high-frequency gravitational waves predicted by Gorkavy's hypothesis are found, the usual model will have to say goodbye.

It is unrealistic to explain the features of the observed part of the cosmos on the basis of only the visible part of it. Something invisible makes the "edges" of galaxies rotate at a higher speed than "supposed"; the other "invisible hand" seems to be stretching space-time in all directions faster and faster (the accelerating expansion of the universe). For the discovery of these facts, they have already managed to write out Nobel Prizes many times, and billions of dollars have been spent on the search for the corresponding "dark forces". But there is a nuance: it is likely that no dark matter particles actually exist, and the accelerating expansion of the Universe may turn out to be an illusion at all. The invisible mass spinning galaxies is a multitude of medium-sized black holes, and the apparent acceleration of the expansion is provided by a giant black mega-superhole. But first things first.

Very dark affairs

Back in 1884, Lord Kelvin drew attention to a strange fact: the stars in the outer regions of the disk of our Galaxy revolve around its center much faster than they should, judging by the calculations. This is possible if they are "spun" by the gravity of some mass lying even further, where the stars end and intergalactic space begins. But what lies where the stars end, it was not possible to understand. The famous French mathematician Henri PoincarĂ©, discussing this conclusion of Kelvin, in 1906 for the first time used the phrase "dark matter". The next hundred years have confirmed that the picture is the same in almost all observed galaxies.

There have been many hypotheses about what exactly makes up the dark mass, but most of them are poorly compatible with the observable universe. Over time, one was chosen - about "cold dark matter", theoretically consisting of massive particles (WIMPs) that do not interact with photons of light. Moreover, in such a hypothesis, the mass of WIMPs should be several times greater than that of all ordinary, baryonic, matter. This well explained both the invisibility of dark matter and its powerful effect on galactic disks.

With all the positive properties of WIMPs, they also have a significant drawback: they turned out to be absolutely impossible to find in experiments. Large and expensive accelerators have shown long ago that if there are such particles, then their size is so small that it is unrealistic to detect them by their effect on other particles. The WIMP cross-section, according to such experiments, cannot be much larger-45meters, which is ten orders of magnitude less than the Planck length. And the Planck length is generally the limit of distance, less than which the very concepts of space and length cease to have any meaning. Any attempt to investigate a smaller object (less than 1.6⋅ten-35meters) will require a collision of high-energy particles, which will inevitably end with the birth of a black hole: instead of crushing the particles into smaller pieces, this will lead to the "sticking" of particles into a negligible BH. It's a pity - the Wimps looked like an excellent, logical hypothesis .

A similar story happened with dark energy. There are two good ways to measure the distance to galaxies: according to Hubble's law (the distance is proportional to the redshift, the elongation of light waves that have come down to us from a distant galaxy) and by "standard candles", type Ia supernovae. Such supernovae, in theory, explode upon reaching the same threshold mass, that is, their brightness is practically the same. Looking at their apparent brightness and correlating it with such a supernova explosion energy (directly related to mass), it is easy to calculate what is the distance to a distant galaxy. But these two methods, as it turned out, give conflicting results. In distant galaxies, the distance to which was determined according to Hubble's law, type Ia supernovae have a brightness lower than "expected"! That is, somehow the distance which the photons passed from the outbreaks of these supernovae turned out to be more than it should be - as if the space between us had stretched out, and along with it the light waves from these flares stretched out (becoming "redder", that is, longer). These observations were interpreted as the accelerating expansion of the universe, and for this discovery was successfully awarded the Nobel Prize.

It remains to find out the sheer little thing: what exactly stretches space-time and makes the Universe move with acceleration. At the moment, it is believed that this is some kind of repulsive dark energy with a density of the order often-29g / cm³. But with such a density, one cannot even dream of discovering it in an experiment. How, then, to study what cannot be studied in the laboratory? That's right, purely in theory. All attempts to limit the properties of dark energy by observing large structures of the Universe have not yet yielded serious results. Therefore, it is considered either the energy of the vacuum, or the particle-like excitation of a certain dynamic scalar field ("quintessence"), or whatever else. However, when they move from hypotheses to calculations, one confusion turns out. If dark energy is vacuum energy (the least complicated hypothesis), then it should be predicted by quantum field theory. But the value of the vacuum energy, which it predicts, is 120 orders of magnitude greater than that which follows from observations of the accelerating expansion of the Universe. This is such a big gap that there is nothing even to discuss here.

Dark energy "in black"

Around 2003, physicist Nikolai Gorkavy, who had previously dealt with purely "gravitational" problems - such as the rings of Uranus and its satellites, the existence of a number of which he predicted from the shape of the rings and before their discovery by astronomers - tried to approach "dark matter" from the other side. Based on the "gravitational" vision of the world, the researcher decided to find out what the effect of black holes of various sizes on the universe around us might be. He was especially interested in the processes of BH mergers, in which a significant part of the mass of both of them turns into gravitational waves (oscillations of space-time). If BHs themselves completely attract matter, then gravitational waves do not. Thus, it turns out that in mergers of black holes the mass seems to "disappear", but in fact, turns into the energy of gravitational waves.

Based on this model, the scientist turned to the hypothesis put forward by the creator of the term “Big Bang”, Georgy Gamov, that the Universe expands and contracts cyclically. According to the calculations of Gorkavy and his co-author Vasilkov, it turns out that during compression at the end of each cycle of existence of the Universe, black holes stick together into ever-larger objects, simultaneously absorbing "little things" such as stars and planets. In each such merger, only a few percent of their mass is converted into the energy of gravitational waves, but since there are a lot of such mergers, in the end, a significant portion of the mass of the Universe is converted into energy of gravitational waves. At this moment, there is a kind of jump: in a short astronomical time, the disappearance of a significant mass of the contracting Universe does not generate a funnel of gravitational potential, but a peak of this potential, which causes the rest of the Universe to expand in all directions.

From the outside, it will look exactly like an explosion, in which the debris fly in different directions. This is exactly how, in the framework of the hypothesis of Gorkavy and Vasilkov, the compression cycle of the former Universe was replaced by the expansion cycle of the present Universe.

It would seem, what does dark matter and dark energy have to do with it? In fact, the connection is the most direct. First, at the end of a series of BH mergers from the past Universe, the largest of all black holes should have appeared. Naturally, such a hole has a huge impact on the space-time surrounding it. By absorbing the energy of gravitational waves, it will continue to rapidly increase its mass, further strengthening its gravitational field.

As a result, the gravity from it will be so powerful and rapidly increasing that the first early galaxies of the Universe, scattering to the sides, at a certain moment will feel an increasing deceleration: those of them that are closer to the ancient hyper massive black hole will slow down, and those that are further away, will continue to fly with less deceleration. Due to this, photons from more distant galaxies will appear "redder" than they are, which means that the redshift from distant objects will differ from what is expected. 

As you know, the distance to distant galaxies is determined precisely by the redshift. So, its "correction" by a hyper massive black hole will create an illusion of an accelerating expansion of the Universe for the terrestrial observer, despite the fact that in practice such an accelerating expansion will not occur. In Gorkovy's model, the Universe, of course, also expands, but without real increasing acceleration. So, we have found a good candidate for the role of dark energy - a hyper massive black hole. Importantly, the correctness of such a scenario - and the very existence of such a huge ancient BH - can be fully verified through observations, which cannot be said about dark energy in the framework of the hypothesis that it is the energy of a vacuum.

Dark matter "in black"

Within the framework of such a "bounce cosmology", not only distant distances but also the neighborhood of our own Galaxy, begin to look differently. If immediately after the Big Bang almost all the mass of the former Universe turned into gravitational waves, then their energy should dominate in the space around us until now. According to calculations from Gorkavy's last article, the Universe is about 99% composed of ancient, relict gravitational waves and ~ 1% - from black holes, baryons, and other particles. Meanwhile, black holes absorb gravitational waves, and in this case, the energy of such waves is again converted back into the mass of its BH traps. Although the most energetic increase in mass will be the ancient hypermassive hole, in addition to it, a set of less massive BHs should have remained in the Universe from the last cycle. Some of them will become "seeds" for those black holes

But there will be many other black holes - intermediate masses, once formed during the collapse of stars, and then rapidly gaining mass due to the surrounding matter and gravitational waves. Many of them will find themselves outside the visible disk of galaxies, where gas has accumulated, from which visible stars are formed. Their gravity will spin the peripheral regions of the visible galactic disks and thereby play the role of dark matter.

Before Gorkavy's model, the assumption that dark matter is black holes on the outskirts of galaxies had already been put forward. But she was not very popular. The fact is that black holes should be formed from stars, and there simply could not be many such stars outside the galactic disks - which means that there cannot be many BHs there. In "bounce cosmology" everything is different: black holes from past cycles of compression and expansion of the Universe may well concentrate on the outskirts of galaxies, where there have never been stars. After all, such holes were formed from stars not in this cycle of the existence of the Universe, but much earlier.

Pros and cons

Of course, such a hypothesis is much broader in scope than earlier hypotheses about wimps or dark energy, so it can explain many more things, which is undoubtedly a plus.

Take the baryon asymmetry of the universe. As you know, we see a lot of ordinary matter around us and almost do not see antimatter. If there were equal numbers of them, atoms would annihilate with antiatoms and the entire Universe would be filled with photons without any atoms at all. Obviously, for some reason, there was much more common matter from the very beginning than antimatter. Now physics considers this to be one of the still-unsolved problems.

Within the framework of Gorky's model, the situation is completely different. The cyclic Universe assumes a large (or even very large) number of cosmological cycles, which greatly simplifies the solution of the problem of the "superiority" of ordinary, baryonic matter over antimatter. There is a lot of time in a cyclic Universe: baryons can slowly accumulate in each cycle, while antimatter disappearing due to annihilation with ordinary matter, on the contrary, will be less and less.

Another big plus of the hypothesis is the absence of the need for wimps, which, frankly, no one has seen in any experiment, as well as dark energy, which, due to its low hypothetical density, no one hoped to see from the very beginning. Gorkavy's model needs only the general theory of relativity, which has been quite well proven to date, and even a gravitational wave detector in order to register those high-frequency gravitational waves that, within the framework of cyclic cosmology, should constitute the bulk of the energy of the Universe. Alas, the existing LIGO detector system is optimized for capturing low-frequency gravitational waves and is not suitable for such a search. But the shorter the wavelength and the higher the frequency of the wave, the more its energy, that is, it will be possible to find traces of the past cycle with the help of more compact detectors than the same LIGO.

The hypothesis also has disadvantages, but in many respects, they are not physical, but psychological. The model of wimps, dark matter from unknown particles, as well as dark energy of an obscure nature, is too deeply rooted in the minds of many researchers, much like the concept of aether in the 19th century. In addition, just as with ether, which was considered "imperceptible for matter", due to the "imperceptibility" (inaccessibility for experimental research) of TM and DE, insisting on their existence can be quite long: it is difficult to refute the existence of something intangible. And too much effort was spent on searching for TM / TE - psychologically it will be quite difficult to admit all this as a delusion of the same type of ether. Fortunately, in the end, everything is quite simple in physics: if the high-frequency gravitational waves predicted by Gorkavy's model are found.

It is possible that in fact, no dark matter and energy in their usual representation exists.

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