Nearly 100 years since the existence of dark matter was first proposed, we may have discovered a direct imprint of it at the center of the Milky Way.
It was 1937 when the Swiss astronomer Fritz Zwicky first hypothesized, by observing several galaxies within the Coma cluster and trying to approximate their mass, that the cluster must be held together by an invisible “dark matter”. Today, after almost a century, research based on data from NASA’s Fermi gamma-ray space telescope may have provided the first direct evidence of the existence of dark matter. The study, led by Tomonori Totani, an astronomer at the University of Tokyo, was published in Journal of Cosmology and Astroparticle Physics.
So far there was only indirect evidence
It is thought that dark matter makes up about 26% of what exists in the Universe and that its quantity is five times greater than the ordinary matter of which we and what we know are made. Until now, the presence of dark matter in galaxies had only been deduced indirectly, because dark matter does not interact, except weakly, with ordinary matter. However, it makes itself felt with its gravitational force which is thought to hold galaxies together, influence the speed of stars and gases, deform space-time causing the effect of gravitational lenses (to learn more).
Energy destruction
One of the most accepted explanations is that dark matter is made up of weakly interacting particles of great mass (weakly interacting massive particlesWIMP), which are heavier than protons and interact very weakly with normal matter. When two WIMPs collide, they annihilate each other (completely destroy each other), producing more familiar particles, including gamma rays.
Tomonori Totani is convinced that he has detected the specific gamma rays of this process at the center of the Milky Way, hypothetically a direct “signature” of the presence of dark matter.
The hand of dark matter?
“We detected gamma rays with a photon energy of 20 gigaelectronvolts (or 20 billion electronvolts, an extremely high amount of energy) extending in a halo-like structure towards the center of the Milky Way,” says the scientist who started from an analysis of data from the Fermi telescope. «The emission component of gamma rays corresponds closely to the shape expected from the dark matter halo».
The emission intensity of gamma rays also corresponds to the emission that should be produced by the destruction process of hypothetical WIMP particles, candidate components of dark matter, and the same goes for the frequency of gamma ray emission. In short, these emissions in that area of the Milky Way do not seem to be easily explained by other known astronomical phenomena.
Waiting for confirmation
The results of the Japanese group will need to be verified by other researchers independently. It will be necessary to confirm that similar radiation propagating as in a halo cannot be caused by other phenomena, and also to look for further evidence of collisions between WIMP particles with the respective energy signature also in other locations that are suspected of hosting large quantities of dark matter.
