Physicists urged to close dark matter

(ORDO NEWS) — A group of scientists believe that the presence of barred galaxies indicates that the traditional cosmological model and the standard theory of gravity are wrong. Despite the correctness of some of this criticism, the proposed modification of physical theories also raises questions.

New work in Symmetry focuses on the fact that observed typical galactic structures seem to be inconsistent with the presence of dark matter in galaxies.

As the authors of the study believe in this regard, it is not there, and the observed oddities in the rotation of galactic disks indicate that we misunderstand the nature of gravity.

The article takes a new approach to showing the incorrectness of the standard cosmological model, suggesting instead a version of MOND – a hypothesis of modified Newtonian dynamics, according to which the law of universal gravitation simply does not work for small accelerations.

About half a century ago, astronomers received reliable observational evidence that the disks of the galaxy – and ours too – are behaving abnormally. In the solar system, the farther the planet is from the star, the slower it follows the trajectory around it.

Judging by the known data on exoplanets, the same is the case in other planetary systems. But in galaxies, instead, the speed of rotation of stars at the edges of galactic disks (relative to galactic centers) is approximately the same as at the core itself.

From this, it was concluded that there are some invisible – in all ranges – objects surrounding the galaxies, which, with their gravity, spin the edges of these disks.

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A number of galaxies behave as if there is no or almost no dark matter in them. MOND cannot explain this, in contrast to the standard cosmological theory, which attributes the difference in behavior to the different evolution of such galaxies (their stripping off by more massive ones). The authors of the new work suggest that there are some observational inaccuracies for all such galaxies

The presence of such “dark matter” also simplified the understanding of the results of observations of the inhomogeneity of the Universe. Gravitational lensing data also indicated that many galaxies have a mass greater than that, and this follows from observations of them in the optical or any other range.

Such a hypothesis of “dark matter” was logical, but required an explanation of what it is. For decades, physicists have assumed that these are some exotic WIMP particles that have mass, but do not interact with photons of all types of radiation. The problem turned out to be that such particles were not detected in any experiments.

In 1983, they proposed a different approach to solving the problem – MOND, modified Newtonian dynamics.

According to it, at the edges of galactic disks, where the action of gravity of matter from the galactic core weakens (due to huge distances from it), the law of universal gravitation changes – and in such a way that objects in such zones can move around the center of galaxies much faster than the standard representation allows about gravity.

The problem with MOND, however, was that it did not explain well the dynamics in clusters and superclusters of galaxies. There it was more like that there is still some invisible mass – otherwise it was difficult to explain the movements of large clusters of galaxies.

The authors of the new paper proposed something like a hybrid approach with a strong bias towards MOND. In their opinion, it is logical to assume that a light sterile neutrino has a mass.

Such a hypothetical variety of neutrino is called sterile, which not only interacts very weakly with matter, like an ordinary neutrino, but does not interact with it at all, except gravitationally.

To date, it has been shown that if such particles exist, then their mass is below hundreds of electron volts. Consequently, they cannot give the Universe enough mass to “close” all the need for dark matter.

The researchers tried to explain the “non-Mondian” dynamics in galaxy clusters due to the fact that sterile neutrinos still exist, it’s just that their mass is small – below hundreds of electron volts – and affects the state of affairs only on large scales, for example, in clusters. But on the scale of galaxies, MOND also predicts everything well.

Scientists conclude that their version has more predictive power than the standard cosmological model. The latter indicates that the dynamics of disk edges in different galaxies can be different, since the evolution of one or another galaxy can differ. As a result, the amount of dark matter in one may be less than in the other (NS wrote about such cases here).

From the point of view of the authors of the new work, the fact that MOND does not need to take into account the evolution of each galaxy speaks of its “greater predictive power.”

At the same time, for cases where MOND does not explain the speed of movement of the edges of galaxies (“galaxies without dark matter”, within the framework of standard cosmological theory), the researchers suggest some “insufficiency of data”.

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NGC 1300, a barred spiral galaxy (bright longitudinal detail in the center)

The work is interesting because it raises really acute problems. For example, its authors are right when they note that barred spiral galaxies indicate that there is practically no dark matter in the galactic disks themselves.

A “bar” in a spiral galaxy is a region of bright stars that emerges from the galactic center and crosses the galaxy in the middle. It is present in two-thirds of spiral galaxies, including our own Milky Way.

The bars rotate, and if the galaxies were the owners of a large amount of dark matter, it would slow them down over time. However, most barred spiral galaxies do not slow down. This is a fairly serious argument in favor of the fact that there is no dark matter in the galaxy itself.

It should be noted that a number of researchers offer other ways to solve the problem of dark matter without modifying the law of universal gravitation. For example, Nikolai Gorkavy, relying on LIGO data, indicates the presence in the Universe of a large number of medium-mass black holes.

He notes that globular clusters of such objects can play the role of dark matter, requiring neither a modification of the gravitational laws, nor the introduction of some exotic and by no means detectable elementary particles such as WIMPs or sterile neutrinos.

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