If there is something that physicists thought they knew about dark matter, it is that, since it does not emit any type of electromagnetic radiation, its particles could not interact with those of ordinary matter, which form planets, stars and galaxies, except through the gravity.
But a new study carried out by scientists at the Higher International School for Advanced Studies (SISSA), in Italy, has found, for the first time, evidence of a direct interaction between the two types of matter.
In a recent article published in 'Astronomy & Astrophysics', in fact, the researchers suggest that at the center of spiral galaxies there is a vast scientific region made up mainly of dark matter particles in
which these particles interact with those of ordinary matter. Something that came into direct conflict with the dominant theories.
In the study, led by Gauri Sharma and Paolo Salucci of SISSA and Glen Van der Vev of the University of Vienna, the researchers examined a large number of galaxies, from those closest to our own located more than 7.000 billion of years. distance light.
According to the authors, this new research represents a major step forward in our understanding of dark matter, the elusive substance that physicists have been unsuccessfully pursuing for decades. Because it does not emit any radiation, dark matter cannot be detected directly with telescopes. But scientists know it's there because of the gravitational effects it has on ordinary matter, which we can see. Four times more abundant than the material that formed stars and galaxies, the dark material is considered to be the 'skeleton' of the Universe. Without it, the galaxies and large structures that we observe could not exist.
"Its dominant presence in all galaxies - explains Gauri Sharma - arises from the fact that the stars and hydrogen gas move as if they were governed by an invisible element". And until now, attempts to observe that 'element' have focused on nearby galaxies.
Compare ancient galaxies
“However, continues the researcher, in this study we try, for the first time, to observe and determine the mass distribution of spiral galaxies with the same morphology as the closest ones, but much further away, up to a distance of 7.000 million. of light years
Paolo Salucci, for his part, adds that "by studying the movement of stars in approximately 300 distant galaxies, we discovered that these objects also have a halo of matter and that, starting from the center of a galaxy, this halo indeed has a dark region in which its density is constant. A feature, by the way, that he had already observed in sober studies of nearby galaxies, some of which were also the work of SISSA.
Getting bigger and bigger
The new research has revealed that this central region had something totally unexpected and unforeseen in the so-called 'standard model of cosmology'. For Sharma, "as a result of the contrast between the properties of nearby and distant spiral galaxies, that is, between current galaxies and their
ancestors of seven millennia of years ago, we could see that our only unexplained region with a constant density of dark matter exists, but also that its dimensions increase over time, as if these regions were subject to a process of expansion continues and dilution.” Something very difficult to explain if, as predicted by the current theory, there is no interaction between the particles of dark matter with those of ordinary matter.
"In our research - adds Sharma - we offer evidence of interaction between dark matter and ordinary matter that, over time, slowly builds a region of constant density from the center of the galaxy outwards." But there is more.
"Surprisingly," explains Salucci, "this region with constant density expands with time. It is a very slow process, but inexorable. The simplest explanation is that early on, when the galaxy forms, the distribution of dark matter in the spherical halo matches the theory's prediction, with a density peak in the center. Subsequently, a galactic disk that characterizes spiral galaxies was formed, surrounded by a halo of particles of extremely dense darkening material. Over time, the interaction effect we propose means that these particles were captured by the stars, or else ejected towards the outer reaches of the galaxy, proportionally with time and finally reached those of the galactic stellar disk, as we describe in Article".
"The results of the study -concludes Sharma- raise important questions for alternative scenarios that describe dark matter particles (apart from Lambda-CDM, the dominant theory), such as hot Dark Matter, Interactive Dark Matter and Ultralight Dark Matter".
According to the researchers, the properties of very distant galaxies in space and time "offer cosmologists a veritable gateway to finally hearing the mysteries of dark matter."
