Scientists have reported important observations from the indirect light of the first stars in the universe that they suggest could hint at an important piece of the puzzle that is dark matter. Dark matter was proposed in the 60s to explain certain features seen in galaxies, and it became key to our understanding of the universe. However, it has so far eluded all our attempts at detecting it.
Researchers used the EDGES experiment to detect a particular radio signal emitted by the hydrogen gas that surrounded and absorbed the light of the first stars. The signal was almost twice as strong as the theoretical expectations and, in a paper published in Nature, Professor Rennan Barkana points the finger at dark matter.
The strength of the signal suggests that the hydrogen gas was cooler than expected. Using standard thermodynamics, Barkana argues that to cool down the hydrogen, you need something cooler to take away the energy. And that thing could be dark matter.
"I realized that this surprising signal indicates the presence of two actors: the first stars, and dark matter," Professor Barkana, who works at Tel Aviv University, said in a statement. "The first stars in the universe turned on the radio signal, while the dark matter collided with the ordinary matter and cooled it down. Extra-cold material naturally explains the strong radio signal."
Assuming that the cause of the cooling is truly dark matter, it is possible to work out some of its properties. Dark matter particles cannot move at relativistic speed and they have to be light – about several times the mass of the protons. This latter prediction goes against the current consensus, which expects dark matter particles to be significantly heavier.
This is an exciting consequence of an already exciting series of observations, but it shouldn’t be interpreted as a conclusive statement on the nature (or even existence) of dark matter. It's a start, a potential new avenue to uncover its true nature. Barkana believes that dark matter could create a specific pattern in the primordial hydrogen gas observations and that a next-generation radio observatory like the Square Kilometer Array (SKA) could see it.
"Such an observation with the SKA would confirm that the first stars indeed revealed dark matter," added Barkana.
Dark matter is believed to be six times more abundant than the regular matter that makes stars, planets, us, and possums. Together with dark energy (another mysterious component), they make up the standard model of cosmology, which has been used to successfully explain many features observed in the Universe.
