Dark matter exists: observations refute alternative explanations

As fascinating as it is mysterious, dark matter is one of the greatest enigmas of astrophysics and cosmology. It is thought that it accounts for 90% of the matter in the universe, but its existence has only been demonstrated indirectly and has recently been questioned. New research by SISSA dispels recent doubts about the presence of dark matter in galaxies and refutes empirical relationships in support of alternative theories. The study, published in the Astrophysical Journal, also offers new perspectives for understanding the nature of dark matter and its relationship to ordinary matter.

From the expansion of the universe to the motion of stars in galaxies, many phenomena can not be explained by the mere presence of baryonic matter. The force of attraction generated by matter is insufficient to explain the observable gravitational effects. This led to the theory of the existence of undetectable dark matter and the idea that galaxies are embedded in its spherical halo.

"Three years ago, a few colleagues at Case Western Reserve University raised questions about our understanding of the universe and the extensive work of many researchers, casting doubt on the existence of dark matter in galaxies, "explains Chiara Di Paolo, PhD student studying astrophysics at SISSA. "By analyzing the rotation curves of 153 galaxies, mainly of the" classical "spiral type, they obtained an empirical relation between the total gravitational acceleration of stars (observed) and the component that we would observe in the presence of ordinary matter in the classical Newton This empirical relation, which seemed valid in all the galaxies analyzed and whatever their radius, motivated the explanation of the gravitational acceleration without necessarily calling into question the dark matter, but implying, for example , modified-gravity theories such as Modified Newtonian Dynamics (MOND). "

Di Paolo and his collaborators wanted to verify this relationship by analyzing the rotation curves of galaxies other than the classical spiral type: 72 low surface gloss galaxies (LSB) and 34 dwarf disk galaxies. They produced more extensive results, finding a relation which, in addition to the total gravitational acceleration and its ordinary component, also implies the galactic radius and morphology of the galaxies.

"We have studied the relationship between total acceleration and its ordinary component in 106 galaxies, obtaining results different from those previously observed," says Paolo Salucci, professor of astrophysics at SISSA and one authors of the research. "This not only demonstrates the inaccuracy of the empirical relationship described above, but also eliminates doubts about the existence of dark matter in galaxies, and the new relationship found could provide crucial insights into understanding." of the nature of this indefinite component. "