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, the ones that form planets, stars and galaxies, except through the gravity.
But a new study 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 an article recently published in ‘Astronomy & Astrophysics’, in fact, the researchers suggest that at the center of spiral galaxies there is a vast spherical region made up mostly of dark matter particles in
which these particles interact with those of ordinary matter. Something that directly conflicts 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 the closest to others located more than 7 billion miles away. light years away.
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 matter that forms stars and galaxies, dark matter 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 ruled by an invisible element”. And until now, attempts to observe that ‘element’ have focused on nearby galaxies.
Compare with ancient galaxies
“However – continues the researcher – in this study we try, for the first time, to observe and determine the distribution of the mass of spiral galaxies with the same morphology as the closest ones, but much further away, up to a distance of 7,000 million light-years. The idea is essentially that these progenitors of spiral galaxies like our own could offer fundamental clues about the nature of the particle that is supposed to exist at the heart of the mysterious dark matter.”
Paolo Salucci, for his part, adds that “by studying the movement of stars in approximately 300 distant galaxies, we discovered that these objects also had a halo of dark matter and that, starting from the center of a galaxy, this halo indeed has a region in which its density is constant. A feature, by the way, that had already been observed in 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 billion years ago, we could see that not only does an unexplained region exist with a constant density of dark matter, but also that its dimensions increase over time, as if those regions were subject to a process of continuous expansion and dilution .” Something very difficult to explain if, as current theory predicts, 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 over time. It is a very slow process, but inexorable. The simplest explanation is that at the beginning, when the galaxy was formed, the distribution of dark matter in the The spherical halo coincides with that predicted by theory, with a density peak in the center.Later, the galactic disk that characterizes spiral galaxies is formed, surrounded by a halo of extremely dense dark matter particles.With the passage of the time, the interaction effect we propose means that these particles were either captured by stars, or else expelled to the outer reaches of the galaxy.This process creates a spherical region of constant density within the dark matter halo, with dimensions increasing proportionally with time and finally reach those of the galactic stellar disk, as we describe in the 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 the hot dark matterthe Interactive Dark Matter and the Ultraligera Dark Matter”.
According to the researchers, the properties of very distant galaxies in space and time “offer cosmologists a true gateway to finally understand the mysteries of dark matter.”