Ten galaxies in the vicinity of our own do not behave at all as predicted by the dominant physical model, and this makes some scientists talk about the need to modify it.
Researchers from the University of St Andrews (Scotland, UK) have come to the conclusion that the parameters of a dozen nearby galaxies seem to contradict modern concepts of gravity and dark matter. In their opinion, the problem can be solved by invoking modified Newtonian dynamics, an alternative theory of gravity, proposing a change in Newton's law of gravitation. Due to this, it explains the rotation of galaxies without attracting dark matter. A related article was published in the Monthly Notices of the Royal Astronomical Society.
The behavior of nearby galaxies is inexplicable from the point of view of dark matter, so a group of astronomers proposes to modify the theory of gravity
Scientists have collected data on the speed and direction of movement of 30 nearby galaxies. Most of them are small satellite galaxies of two large ones - ours (the Milky Way) and the Andromeda Nebula (even larger, 2.5 million light-years from us). It turned out that the trajectories of about a dozen dwarf galaxies are lined up in a very strange way. All of them seemed to have been untwisted by a sling: in the past, their trajectories fell from orbits close to two large host galaxies.
In principle, such a scenario is not difficult to calculate: if the Milky Way and the Andromeda Nebula passed close to each other about 6-7 billion years ago, then they mutually slowed down their rotation. In this case, part of the dwarf satellite galaxies was torn from their orbits, as the central part of the sling rips off a stone from the bed of a sling when it is thrown and slowed down.
The problem with this explanation is that, according to the dominant physical model, galaxies are immersed in a cloud of invisible cold dark matter that makes up the bulk of their masses. If the Milky Way and Andromeda were so close and slowed down the rotation of each other, then they should have started merging 6-7 billion years ago. In practice, this is not visible: according to calculations, they will merge only after a few billion years.
The authors suggest a way out of this problem. In their opinion, for this it is necessary to use modified Newtonian dynamics (MOND). Under the MOND hypothesis, dark matter does not exist, and the observed oddities in the rotation of stars around the centers of their galaxies are explained by a simple modification of Newtonian gravity. Then the mass of both mentioned large galaxies is less than what it is considered now. Consequently, their convergence with a moderate deceleration of rotation should not have led to a merger.
It should be noted that in addition to MOND, there are other hypotheses explaining the behavior of galaxies without dark matter. At present, an article by Nikolai Gorkavy is being prepared for publication in a peer-reviewed journal, in which relic gravitational waves are used for these purposes.
Promotional video:
