Galaxies can exist without dark matter. We tell you how this is possible

What is dark matter?

Dark matter in astronomy and cosmology, as well as in theoretical physics - form

matter not participating in the electromagneticinteraction and therefore inaccessible to direct observation. It is about a quarter of the mass-energy of the Universe and manifests itself only in gravitational interaction.

The concept of dark matter is introduced for the theoreticalexplanations of the hidden mass problem in the effects of anomalously high rotation speed of the outer regions of galaxies and gravitational lensing (they involve matter whose mass is much greater than the mass of ordinary visible matter); among others, it is the most satisfactory.

The composition and nature of dark matter on the realmoment unknown. In the framework of the generally accepted cosmological model, the model of cold dark matter is considered the most probable. The most likely candidates for the role of particles are wimps. Despite active searches, they have not yet been found experimentally.

The term “dark matter” itself may be the firstwas used to estimate the mass of the stars in the galaxy based on the distribution of their velocities. Ultimately, the term began to be used precisely in the sense of unobservable matter, the existence of which can be judged only by its gravitational effect. 

Three-dimensional map of the distribution of dark matter, built using the method of weak gravitational lensing in the framework of the COSMOS project.

Alternative theories of the existence of dark matter

  • Alternative theories of gravity

When trying to explain the observed phenomena,On the basis of which, in the aggregate, a conclusion was made about the necessity of the existence of dark matter, without involving this concept, considerations were first expressed regarding the validity of the generally accepted laws of gravitational interaction at large distances.

The most famous is the modifiedNewtonian dynamics (MOND) is a theory proposed in the early 1980s by Israeli astrophysicist Mordechai Milgrom that is a modification of the law of gravity that produces stronger interactions in some regions of space in a way that explains the observed shape of the rotation curves of galaxies.

In 2004, theoretical physicist YaakovBekenstein, also from Israel, developed a relativistic generalization of this hypothesis - the tensor-vector-scalar theory of gravity, which also explains the observed effects of gravitational lensing.

In addition, in 2007, Canadian physicist John Moffat proposed his theory of modified gravity, also called scalar-tensor-vector theory of gravity. 

Proponents of modified gravity theoriesconsider the current lack of positive results from experiments on the direct detection of dark matter particles as an argument in their favor. 

Meanwhile, currently most scientistsdoes not recognize MOND, since calculations based on it indicate its inconsistency. The problem with alternative theories of gravity is that even if they provide justification for individual effects that are consequences of the existence of dark matter, they still do not take them into account as a whole.

They do not explain the observed behaviorcolliding galaxy clusters and are inconsistent with the cosmological arguments for the presence of large amounts of non-baryonic invisible matter in the early universe.

Abell 2218 Cluster of Galaxies

  • Plasma cosmology

This theory was developed in the 1960sby a Swedish physicist named Hannes Alfven (1970 Nobel laureate for discoveries in magnetodynamics) - in doing so he used the experience of his studies of near-Earth plasma (aurora borealis) and the early work of Christian Birkeland.

The basis of the theory is the assumption thatElectrical forces are more significant at large distances (scale of galaxy and galaxy clusters) than gravity. If we assume that plasma fills the entire universe and has good conductivity, then it could conduct enormous electric currents (about 1017–1019 amperes) on scales of tens of megaparsecs.

Such currents create a powerful galactic magnetic field, which in turn forms the structure of both galaxies and their clusters (galactic threads or filaments).

The presence of such a powerful field easily explainsthe formation of galactic arms (there is no consensus yet on the reason for the formation of galactic arms), the distribution of the rotation speed of galactic disks from the radius, eliminates the need to introduce a halo of dark matter.

But at the moment, modern astrophysics does not observe such powerful currents on a scale of tens of megaparsecs, nor high intergalactic and intragalactic magnetic fields.

Plasma cosmology assumptions aboutThe filamentous cell structure and homogeneity of the Universe on large scales (the so-called Large-Scale Structure of the Universe), made by Alfvén and Anthony Perrat, were unexpectedly confirmed by observations in the late 1980s and 1990s, but these observations are also explained within the framework of generally accepted cosmological models.

To explain the filamentary structure of the Universe inCurrently, the theory of the formation of filaments due to gravitational instability is used (initially, an almost uniform distribution of mass is concentrated on caustics and leads to the formation of filaments), on growing structures of dark matter, along which the structure of visible matter is formed (the origin of such a structure of dark matter is explained by quantum fluctuations in process of inflation).

Currently, plasma cosmology asthe theory is unpopular, since it denies the development of the Universe along the path of the Big Bang. On the other hand, if we abandon the Big Bang theory and consider the age of the Universe to be much greater than 13.5 billion years, then the latent mass can be largely explained by such MACHO objects as black dwarfs, which evolve from white dwarfs that have cooled down over tens of billions of years ...

  • Matter from other dimensions (parallel universes)

Some extra-dimensional theories accept gravity as a unique type of force that can act on our extra-dimensional space.

This assumption helps explainthe relative weakness of the gravitational interaction in comparison with the other three basic interactions (electromagnetic, strong and weak): gravity is weaker, since it can interact with massive matter in extra dimensions, penetrate a barrier inaccessible to other interactions.

It follows that the dark matter effect canbe logically explained by the interaction of visible matter from our ordinary dimensions with massive matter from other (extra, invisible) dimensions through gravity. At the same time, these dimensions and this matter in them cannot feel other types of interactions in any way, cannot interact with it.

Matter in other dimensions (actually inparallel Universe) can form into structures (galaxies, clusters of galaxies, filaments) in a way similar to our measurements or form their own, exotic structures, which in our measurements are felt as a gravitational halo around visible galaxies. 

Results of numerical modeling of the evolution of the structure of the Universe

  • Topological space defects

Dark matter may just be primordial(arising at the time of the Big Bang) defects in space and / or the topology of quantum fields that can contain energy, thereby causing gravitational forces.

This assumption can be explored andverified using an orbital network of space probes (around the Earth or within the Solar System) equipped with an accurate, continuously synchronized (using GPS) atomic clock that will record the passage of such a topological defect through this network.

The effect will appear as unexplained (commonrelativistic reasons) mismatch of the course of these clocks, which has a clear beginning and, with time, the end (depending on the direction of movement and the size of such a topological defect).

Galaxy without dark matter

Scientists are finding galaxies without dark matter, but it’s impossible to explain how they formed.

  • NGC1052-DF2

In the NGC1052-DF2 galaxy, there is at least 400 times less dark matter than there should be.

Results of measurements carried out usingThe 10-meter telescope of the Keck Observatory and the Hubble Space Telescope (these are the best astronomical instruments available today) also admit that there is no dark matter at all in NGC1052-DF2.

This galaxy, visible only through large telescopes,has a total luminosity at the level of 100 million stars like the Sun, and its mass is approximately 200 million times higher than the mass of the Sun - according to these parameters, NGC1052-DF2 does not stand out too much from the general series.

But what is found inside her tenrelatively bright objects, and due to this, in a number of images, the galaxy turns out to be a set of bright points instead of a blurry cloud, is already a much more interesting fact; it was he who forced astronomers to deploy telescopes with a tightly packed work schedule towards NGC1052-DF2.

According to the researchers, these bright spotsare globular star clusters, but their number and distribution of luminosities are so unusual that astronomers even refused to talk in detail about these objects in this publication and promised to return to this in more detail in another publication, still in the process of preparation.

 If we compare NGC1052-DF2 with othersgalaxies of the same mass, then the invisible halo of dark matter should be four hundred times heavier than what astronomers find, an extremely unusual result.

  • NGC 1052-DF4

Scientists describe results of additionalobservations that allowed more reliable estimates of velocity dispersion to be made based on stellar motions. As a result, astronomers received a value of 8.5 kilometers per second with noticeably smaller errors (about 30%).

From these data it follows that the total massthe galaxy is approximately equal to the mass of the luminous substance, which eliminates the need for the introduction of dark matter in this case. Scientists also discovered nearby a similar galaxy NGC 1052-DF4, which also had an extremely low dispersion of stellar velocities - about 4.2 kilometers per second, but the errors in this case are about 80%.

According to the authors, the data obtained are highqualities provide compelling evidence for the existence of not just one exceptional galaxy without dark matter, but also a new class of similar objects.

They also remind you that these results are notin no way refute the hypothesis of dark matter, but, on the contrary, confirm its necessity: if the effects described by it were actually generated by ordinary matter, then such a situation could not arise, and since an object without dark matter is found, then this speaks precisely of the existence of two separate types of substances that are not directly related.

How can galaxies exist without dark matter?

Galaxies that, judging by observations,contain virtually no dark matter - a substance that weakly interacts with surrounding matter, which is believed to be responsible for 26.8% of the mass of the Universe - complicate astronomers' understanding of the nature of this matter.

Such objects discovered as a result of recentThese observations challenge the Lambda-CDM cosmological model adopted by astrophysicists, according to which all galaxies should be surrounded by a massive halo of dark matter.

Dark matter-free objects are not verywell studied by astronomers. One way to study the possible mechanisms of their formation is to observe several of them at different stages of development. Processing information about galaxies using a computer model makes it possible to trace their evolution.

In order to understand the structure of theseobjects, scientists modeled their evolution using the Illustris model, which takes into account the life cycles of stars, the influence of supernovae and black holes, and mergers of galaxies. The researchers found in the system created by the model, several "dwarf galaxies" with the same number of stars, the number of globular clusters and the mass of dark matter.

As the name suggests, a dwarf galaxyis small and consists of several billion stars. In contrast, the Milky Way, which is orbited by more than 20 known dwarf galaxies, has between 200 and 400 billion stars.

Globular clusters are often used to assesscontent of dark matter in galaxies, especially in small ones. Astrophysicists have found that dwarf galaxies have lost 90% of their dark matter as a result of "pushing out" of their constituent material by their own gravitational forces.

What's the bottom line?

The discovery of black holes without dark matter is not possiblemeans it doesn't exist. On the contrary, a galaxy without a typical distribution of stars by speed undermines the positions of theories that try to attribute the observational results to some universal effect not related to dark matter.

It is in modified Newtonian dynamicsstars should always rotate around the center of galaxies at approximately the same speed, and NGC1052-DF2 plays against this model, which has already lost the support of many experts.

To admit the existence of a galaxy without a darkof matter, modern astrophysics may well, while the idea that the law of universal gravitation works selectively in different parts of the Universe is at least doubtful.

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