Dark matter could originate from the “ordinary” one

The study that overturns the theories on the origin of dark matter: in the beginning dominated the "ordinary" matter, from which originated exponentially the "dark"

That on the origin and composition of dark matter is one of the most fascinating enigmas of science remained unanswered: we are still far from a detailed understanding of what was once called the "missing mass" of the Universe.

Dark matter is the mysterious substance that makes up the "nearly 90% of the matter in the Universe" that we don't know about. It was in 2001 that astronomer Bruce H. Margon of the University of Washington, confessed the embarrassment of the scientific community in "not being able to find" the missing part of the Universe.

"As in a kind of cosmic Ice-9"

A new study published in the journal Physical Review Letters is bound to complicate things, as far as the already mysterious origin of dark matter is concerned. It seems, in fact, that the invisible matter almost completely unknown to humans may originate from what we know quite well about the Universe.

According to the paper - signed among others by Joshua Ruderman, particle physicist at New York University - dark matter could multiply thanks to the conversion of ordinary matter into a type of "darker" substance, "as in a kind of cosmic ice-9".

Ice-9 is a wonderful literary invention of the writer Kurt Vonnegut, who in the 1963 novel "Cat's Cradle" - translated in Italian as "Ghiaccio Nove" - hypothesizes an alternative molecular structure of water, able to solidify at room temperature (to be precise at 45.5°C) and to propagate this property to all the water on the planet, with catastrophic outcomes.

This type of development, based in part on the emanation of certain physicochemical properties, is now referred to in science as exponential growth and is common to several observable patterns in nature, from parasite colonies to the global population of wasps, to name a few.

As Ruderman says, the study began with a simple question, "could dark matter grow exponentially, given its abundance?" So the research team took to confronting one of the mysteries of the Universe, buoyed by Vonnegut's powerful suggestion, with a decidedly fascinating outcome.

In the beginning was ordinary matter

Dark matter we know is the invisible, imperceptible "twin" of ordinary, or baryonic matter and that it makes up, at least according to the latest CERN data, about 85% of the matter in the Universe.

Dark matter is such because it does not interact with light, hence the invisibility that protects its millennia-old secrets, but it produces important gravitational effects on celestial objects, and it is thanks to these interactions that we know today that it exists. Much of what we know today about the Universe, in short, would not make sense if we did not hypothesize the presence of dark matter.

But where does the invisible matter that makes up almost all of the Universe, except what we can see, come from? Early hypotheses on the subject held that dark matter formed in the early stages of the Universe, when particles were mixed together in a kind of primordial electromagnetic "thermal bath." According to this hypothesis, most of what exists would come from dark matter, which would have slowly "destroyed" itself by coming into contact with ordinary matter.

The new study overturns the annihilation theory: in the beginning it was not dark matter, therefore. On the contrary, according to Ruderman and colleagues, at the dawn of the Universe baryonic matter greatly exceeded dark matter, although this did not last long. When a particle of dark matter then came into contact with another particle, the researchers argue, annihilated it thus producing two particles of "antimatter" - in a manner quite similar to what do positrons and electrons that, annihilating produce two photons. And this is what it would look like, today, to the point that dark matter occupies almost the entire Universe.

The new model proposed by Ruderman and colleagues allows for the first time to associate the formation of dark matter with the mechanisms of exponential growth, which would offer a solid explanation for the current composition of the Universe, in which for every particle of baryonic matter there are as many as six of dark matter.

So the new research opens the way to new perspectives of investigation, and infinite new questions, about one of the greatest mysteries of the Universe.