Dark matter may reveal the origin of primordial magnetic fields

The discovery of mini-halos of dark matter scattered throughout the universe could potentially unveil the mysteries of primordial magnetic fields, according to a new theoretical study by the International School for Advanced Studies (SISSA) in Italy.

Magnetic fields 

Magnetic fields, omnipresent on a colossal scale across the universe, have origins that continue to intrigue and puzzle scientists. 

A compelling theory among many in the scientific community is that these magnetic fields are not a later cosmic development but rather primordial, formed near the universe’s inception.

Mini-halos of dark matter

In this study, researchers have suggested a novel approach to probing ancient magnetic fields. They propose that if the fields are indeed primordial, they could lead to an increase in dark matter density perturbations on smaller scales. This process, in turn, could result in the formation of mini-halos of dark matter. 

The detection of these mini-halos would be a significant indicator of the primordial nature of magnetic fields, presenting a paradox where the universe’s unseen components help illuminate aspects of the visible cosmos.

Prevailing hypothesis 

“Magnetic fields are ubiquitous in the Cosmos. A prevailing hypothesis is that the magnetic fields we observe might have been produced in the early stages of the Universe. However, this proposition lacks explanation in the standard model of physics,” said lead author Pranjal Ralegankar, an astrophysicist at SISSA.

“To shed light on this aspect and find a way to detect ‘primordial’ magnetic fields, with this work we propose a method that we could define as ‘indirect.’ Our approach is based on a question: What is the influence of magnetic fields on dark matter?”

Unexpected discovery 

The researchers explored how primordial magnetic fields could amplify the density perturbations of electrons and protons in the early universe. If these perturbations become sufficiently large, they start impacting the magnetic fields. The unexpected result of this interaction, as Ralegankar points out, is the suppression of small-scale fluctuations.

“In the study, we show something unexpected. The growth in baryon density gravitationally induces the growth of dark matter perturbations without the possibility of subsequent cancellation. This would result in their collapse on small scales, producing mini-halos of dark matter.”

Broader implications 

Ralegankar further emphasizes the theoretical implications of their findings: “These theoretical findings also suggest that the abundance of mini-halos is determined not by the present presence of primordial magnetic fields but rather by their strength in the primordial Universe. Thus, a detection of dark matter mini-halos would reinforce the hypothesis that magnetic fields formed very early, even within 1 second after the Big Bang.”

This study represents a significant step forward in our understanding of the universe’s earliest moments. It not only offers a new perspective on the origin of magnetic fields but also highlights the intricate interplay between visible and invisible cosmic components, opening new avenues for exploring the vast and mysterious expanse of our universe.

The research is published in the journal Physical Review Letters.

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