During the “cosmic dawn,” during the early Universe, hydrogen atoms could have interacted with dark matter. Indeed, new research now supports the idea that the detection of surprisingly strong absorption of primordial hydrogen could be substantial evidence of that dark matter that scientists around the world have been pursuing for years.
However, the new results, described in three articles in Physical Review Letters, are merely theoretical and do not solve the problem. Even the group of scientists signing one of the studies is skeptical about the favorable interpretation of the dark matter. However, the work has brought the issue back under the focus, and it is hoped that early next year a new round of observations of the early Universe will be able to settle this matter once and for all.
According to dominant cosmological theories, the hydrogen gas that existed at the beginning of the Universe was in thermal equilibrium with the cosmic microwave background, CMB, which is the residual radiation of the Big Bang. That means that the hydrogen could not have been visible.
Dark matter issue is puzzling, but scientists hope the new experiments would solve this mystery eventually
One hundred million years after the Big Bang, at the beginning of the cosmic dawn, the ultraviolet light of the first stars would have excited those hydrogen atoms, which would have begun to absorb much more radiation, which would be seen as longer wavelengths and displaced in the CMB spectrum.
And it turns out that last February, the researchers of the EDGES experiment, which seeks the “signatures” of reionization during the cosmic dawn, reported in Nature a sudden and punctual “fall” at a wavelength of 380 cm in their instruments. Immediately, theorists began to speculate that hydrogen was, in fact, interacting with dark matter particles.
The idea is that dark matter would have been colder than hydrogen atoms and, therefore, the interactions between the two would have transferred the energy from the gas to the dark matter, thus cooling the hydrogen and increasing absorption.
Some researchers are hoping they’ll finally detect dark matter, while others remain cautiously skeptical. However, new experiments, including SARAS-2, LEDA, and PRIzM raise the hopes that this mystery would be eventually solved.