Invisible "dark matter" in space is forcing galaxies to evolve

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

The longer the mystery of dark matter remains unsolved, the more exotic hypotheses about its nature appear, including the newest idea of the inheritance of giant black holes from the previous Universe.

In order to know that something exists, it is not necessary to see it. So once, according to the gravitational influence on the movement of Uranus, Neptune and Pluto were discovered, and today a search is underway for a hypothetical Planet X on the far outskirts of the solar system. But what if we find such an influence everywhere in the Universe? Take galaxies, for example. It would seem that if the galactic disk rotates, then the speed of the stars should decrease with increasing orbit. This, for example, is the case with the planets of the solar system: the Earth rushes around the Sun at 29.8 km / s, and Pluto at 4.7 km / s. However, already in the 1930s, observations of the Andromeda nebula showed that the speed of rotation of its stars remains almost constant, no matter how far in the periphery they are. This situation is typical for galaxies, and among other reasons, it led to the emergence of the concept of dark matter.

Carnival of problems

It is believed that we do not see it directly: this mysterious substance practically does not interact with ordinary particles, including it does not emit or absorb photons, but we can notice it by the gravitational effect on other bodies. Observations of the motions of stars and clouds of gas make it possible to compile detailed maps of the dark matter halo surrounding the disk of the Milky Way, talking about the important role it plays in the evolution of galaxies, clusters and the entire large-scale structure of the Universe. However, further difficulties begin. What is this mysterious dark matter? What does it consist of and what properties do its particles have?

For many years, WIMPs have been the main candidates for this role - hypothetical particles that are unable to participate in any interactions other than gravitational. They are trying to detect them both indirectly, by the products of rare interactions with ordinary matter, and directly, using powerful instruments, including the Large Hadron Collider. Alas, in both cases, there are no results.

“The scenario in which the LHC finds only the Higgs boson and nothing else has been called a 'nightmare scenario' for a reason,” says Sabine Hossenfelder, a professor at the University of Frankfurt. "The fact that no signs of new physics were found serves me as an unambiguous signal: something is wrong here." Other scientists also picked up this signal. After the publication of negative results of searches for traces of dark matter using the LHC and other instruments, interest in alternative hypotheses about its nature is clearly growing. And some of these solutions look even more exotic than the Brazilian carnival.

Myriad holes

What if WIMPs don't exist? If dark matter is matter that we cannot see, but we see the effects of its gravity, then maybe they are just black holes? Theoretically, at the earliest stages of the evolution of the Universe, they could have formed in huge numbers - not from dead giant stars, but as a result of the collapse of superdense and hot matter that filled the incandescent space. One problem: so far not a single primordial black hole has been found, and it is not known for certain whether they ever existed at all. However, there are enough other black holes in the Universe that are suitable for this role.

Observations of the distant space probe Voyager 1 did not reveal any traces of Hawking radiation, which could indicate the appearance of primordial black holes of microscopic size. However, this does not exclude the existence of larger similar objects. Since 2015, the LIGO interferometer has already registered 11 gravitational waves, and 10 of them were caused by mergers of pairs of black holes with masses of tens of solar masses. This in itself is extremely unexpected, because such objects are formed as a result of supernova explosions, and the deceased star loses most of its mass in the process. It turns out that the precursors of the merged holes were stars of really cyclopean sizes, which should not have been born in the Universe for a long time. Another problem is created by the formation of binary systems by them. A supernova explosion is an event so powerful that any close object will be thrown far away. In other words, LIGO has detected gravitational waves from objects, the appearance of which remains a mystery.

At the end of 2018, such objects were approached by the astrophysicist of the Greenwich Institute of Science and Technology Nikolai Gorkavy and the Nobel laureate John Mather. Their calculations showed that black holes with masses of tens of solar masses could easily add up a galactic halo, which would remain practically invisible for observation and at the same time create all the characteristic anomalies in the structure and movement of galaxies. It would seem, where on the distant periphery of the galaxy come from the required number of such large black holes? After all, the vast majority of massive stars are born and die closer to the center. The answer Gorkavy and Mather give is almost unbelievable: these black holes did not "come", in a certain sense they have always existed, from the very beginning of the Universe. These are the remnants of the previous cycle in an endless sequence of expansions and contractions of the world.

The solid line shows the real orbital velocity of stars and gas orbiting the center of the galaxy; dotted - expected in the absence of the influence of dark matter.

Relics of rebirth

In general, the Big Bounce is not a new model in cosmology, albeit unproven, existing on a par with many other hypotheses of the evolution of the cosmos. It is possible that in the life of the universe, the periods of expansion are indeed replaced by contraction, the "Big Collapse" - and a new bounce-explosion, the birth of the world of the next generation. However, in the new model, these cycles are conducted by black holes, acting as both dark matter and dark energy - a mysterious substance or force causing the accelerated expansion of our Universe.

It is assumed that by absorbing matter and merging with each other, black holes can accumulate more and more of the total mass of the Universe. This should lead to a slowdown in its expansion and then to contraction. On the other hand, when black holes merge, a significant part of their mass is lost with the energy of gravitational waves. Therefore, the resulting hole will be lighter than the sum of its former terms (for example, the first gravitational wave recorded by LIGO was born when black holes of 36 and 29 solar masses merge with the formation of a hole with a mass of "only" 62 solar masses). So the Universe can also lose mass, contracting and filling with ever larger black holes, including one of the largest - the central one.

Finally, after a long series of mergers of black holes, when a significant part of the mass of the Universe "leaks" in the form of gravitational waves, it will begin to scatter in all directions. From the outside it will look like an explosion - the Big Bang. Unlike the classical Big Rebound picture, the complete destruction of the previous world does not occur in such a model, and the new Universe directly inherits some objects from the parent. First of all, these are all the same black holes, ready to again play both main roles in it - both dark matter and dark energy.

Great foremother

So, in this unusual picture, dark matter turns out to be large black holes, which are inherited from the Universe to the Universe. But we must not forget about the "central" black hole, which should form in each such world on the eve of its death and persist in the next. Calculations by astrophysicists have shown that its mass in our today's space can reach an incredible 6 x 1051 kg, 1/20 of the mass of all baryonic matter, and continuously increase. Its growth can lead to an ever more rapid expansion of space-time and manifest itself as an accelerating expansion of the Universe.

Of course, the presence of such a cyclopean mass should lead to the appearance of noticeable inhomogeneities in the large-scale structure of the Universe. There is already a candidate for such heterogeneity - the astronomical Axis of Evil. These are relatively weak, but very alarming signs of the anisotropy of the Universe - the structure that manifests itself in it on the largest scales and does not in any way agree with the classical views on the Big Bang and everything that happened after it.

Along the way, the exotic hypothesis also solves another astronomical riddle - the problem of the unexpectedly early appearance of supermassive black holes. Such objects are located in the centers of large galaxies and managed to gain mass in millions and even billions of solar masses in an unknown way already in the first 1-2 billion years of the existence of the Universe. It is unclear where they could, in principle, find so much substance, and even more so when they could have time to absorb it. But within the framework of the idea with "inherited" black holes, these questions are removed, because their embryos could have gotten to us from the past Universe.

It is a pity that Gorkavy's extravagant hypothesis is still just a hypothesis. For it to become a full-fledged theory, it is necessary that its predictions coincide with observational data - and with such that cannot be explained by traditional models. Of course, future research will make it possible to compare the fantastic calculations with reality, but this will obviously not happen in the near future. Therefore, while the questions about where dark matter is hidden and what dark energy is, remain unanswered.