A group of scientists believe that the presence of jumpers in galaxies indicates that the traditional cosmological model and standard theory of gravity are wrong. Although part of this criticism is correct, a proposed modification of the physical theories also raises questions.
A new paper in Symmetry focuses on the fact that the observed typical galactic structures seem to be incompatible with the presence of dark matter in galaxies. As the authors of the study suggest, it is not there, and the observed oddities in the rotation of galactic disks indicate that we misunderstand the nature of gravity. The paper takes a new approach to showing the incorrectness of the standard cosmological model, proposing instead a kind 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 obtained reliable observational evidence that the disks of galaxies - and ours too - were behaving abnormally. In the solar system, the further away a planet is from a luminary, the slower it follows a trajectory around it. From the known data on exoplanets, this is also the case in other planetary systems. In galaxies, instead, the rotation speed of stars at the edges of galactic disks (relative to galactic centres) is about the same as that of the nucleus itself. From this it was concluded that there are some invisible - in all ranges - objects surrounding galaxies, which by their gravitation untwist the edges of these disks.
The presence of such "dark matter" also simplified the understanding of observations of the inhomogeneity of the Universe. Gravitational lensing data also indicated that many galaxies had a mass above that, and this followed from observations of them in optical or any other range.
Such a 'dark matter' hypothesis was logical, but required an explanation of what it was. For decades, physicists had assumed that it was some exotic particle vimps, having mass but not interacting with photons of all kinds of radiation. The problem turned out to be that such particles have not been detected in any experiments.
In 1983, a different approach to the problem was proposed - MOND, a modified Newtonian dynamics. According to it, at the edges of galactic disks, where the gravitational effects of matter from galactic nucleus weakens (due to huge distances from it), the law of universal gravitation changes - and so that objects in such areas can move around the galactic centre much faster than the standard concept of gravity allows. The problem with MOND, however, was that it did a poor job of explaining the dynamics in galaxy clusters and superclusters. There it was more likely that there was still some kind of invisible mass - otherwise it was difficult to explain the motions of large galaxy clusters.
The authors of the new work proposed something like a hybrid approach, with a strong preponderance in favour of MOND. In their view, it is logical to assume that light sterile neutrinos have mass. A sterile neutrino is the hypothetical form of neutrino that not only interacts with matter very weakly, like a normal neutrino, but does not interact with it at all, except gravitationally. To date, it is shown that such particles, if any, have a mass below hundreds of electronvolts. Consequently, they cannot give the Universe enough mass to "cover" the entire need for dark matter.
The researchers have tried to explain the "non-Mondian" dynamics in galaxy clusters by saying that sterile neutrinos do exist, but their masses are small - below hundreds of electron volts - and affect the situation only on large scales, for example in clusters. But on galaxy scales everything is well predicted by MOND as well.