Dark matter what is actually the most mysterious substance in the universe

(ORDO NEWS) — The longer the mystery of dark matter remains unsolved, the more exotic hypotheses about its nature appear, including the latest idea about the inheritance of giant black holes from the previous Universe.

To know that something exists, it is not necessary to see it. So once Neptune and Pluto were discovered by the gravitational influence on the movement of Uranus, and today a hypothetical Planet X is being searched for on the far outskirts of the solar system.

But what if we find such an influence everywhere in the Universe? Take at least galaxies. It would seem that if the galactic disk rotates, then the speed of the stars should decrease with the growth of the orbit. This is exactly the case, for example, 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, as early as the 1930s, observations of the Andromeda Nebula showed that the speed of rotation of its stars remained almost constant, no matter how far on the periphery they were. This situation is typical for galaxies, and, among other reasons, it led to the concept of dark matter.

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Carnival of problems

It is believed that we do not see it directly: this mysterious substance practically does not interact with ordinary particles, including does not emit or absorb photons, but we can notice it by the gravitational influence on other bodies.

Observations of the movements of stars and gas clouds make it possible to draw up detailed maps of the dark matter halo surrounding the disk of the Milky Way, to talk 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, the main candidates for this role have been WIMPs – hypothetical particles that are unable to participate in any interactions other than gravitational.

They are trying to detect them both indirectly, using the products of rare interactions with ordinary matter, and directly, using the most powerful tools, including the Large Hadron Collider. Alas, in both cases there are no results.

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“The option in which the LHC finds only the Higgs boson and nothing else has been called the “nightmare scenario” for a reason,” says Professor Sabine Hossenfelder at the University of Frankfurt. “The fact that no signs of new physics have been found is a clear signal to me: something is wrong here.”

Other scientists have caught this signal. After the publication of negative results of searches for traces of dark matter using the LHC and other tools, 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 stuff that we can’t see, but we can see the effects of its gravity, then maybe it’s 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 hot 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 suitable for this role.

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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.

In itself, this is extremely unexpected, because such objects are formed as a result of supernova explosions, and the dead star loses most of its mass in the process. It turns out that the predecessors 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 the formation of binary systems by them. A supernova explosion is an event so powerful that any nearby object will be thrown far away. In other words, LIGO has registered gravitational waves from objects whose appearance remains a mystery.

In late 2018, Greenwich Institute of Technology astrophysicist Nikolai Gorkavy and Nobel laureate John Mather turned to such objects.

Their calculations showed that black holes with masses of tens of solar masses could well form a galactic halo, which would remain practically invisible to observations and at the same time create all the characteristic anomalies in the structure and motion of galaxies.

It would seem, where on the far periphery of the galaxy to take 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 given by Gorkavy and Mather is almost unbelievable: these black holes did not “take on”, they always existed in a certain sense, from the very beginning of the Universe. These are the remnants of the previous cycle in an endless series of expansions and contractions of the world.

Relics of Rebirth

In general, the Big Rebound is not a new model in cosmology, although it is 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, periods of expansion really give way to contraction, the “Big Collapse” – and a new rebound-explosion, the birth of the world of the next generation.

However, in the new model, these cycles are orchestrated by black holes, acting as both dark matter and dark energy, a mysterious substance or force that causes the accelerated expansion of our Universe.

It is assumed that, by absorbing matter and merging with each other, black holes can accumulate an increasing part 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 produced by the merger of black holes with masses of 36 and 29 solar masses to form a hole with a mass of “only” 62 solar masses).

This is how the Universe can also lose mass, shrinking and filling up 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 – a Big Bang.

Unlike the classical picture of the Big Rebound, the complete destruction of the previous world does not occur in such a model, and the new Universe directly inherits some objects from the mother. First of all, these are the same black holes, ready to play both main roles in it again – both dark matter and dark energy.

Great Mother

So, in this unusual picture, dark matter turns out to be large black holes that are inherited from Universe to Universe. But we must not forget about the “central” black hole, which should be formed 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 current space can reach an incredible 6 x 10 51 kg, 1/20 of the mass of all baryonic matter – and continuously increase. Its growth can lead to more and 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 disturbing signs of the anisotropy of the Universe – structuredness, which manifests itself in it on the largest scales and is in no way consistent with the classical views of the Big Bang and everything that happened after it.

Dark matter what is actually the most mysterious substance in the universe

Along the way, the exotic hypothesis also solves another astronomical mystery – the problem of the unexpectedly early appearance of supermassive black holes.

Such objects are located in the centers of large galaxies and, by an as yet unknown method, managed to gain a mass of millions and even billions of solar masses already in the first 1–2 billion years of the existence of the Universe.

It is not clear 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 been inherited by us from the past Universe.

It’s a pity that Gorky’s extravagant hypothesis is still just a hypothesis. For it to become a full-fledged theory, its predictions must coincide with observational data – and with those that cannot be explained by traditional models.

Of course, future research will make it possible to compare fantastic calculations with reality, but this will obviously not happen in the near future. Therefore, for now, questions about where dark matter is hiding and what dark energy is remain unanswered.

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