For years astronomers have puzzled over a strange excess of gamma rays coming from the galactic center. Annihilating dark matter has always been a tantalizing explanation, and new research claims that it’s the best answer.
For the last 11 years, NASA’s Fermi-LAT gamma-ray telescope has observed an odd excess of the high-energy radiation coming from the direction of our galactic center. The origin of the gamma rays, which are relatively diffuse around the core, currently has no good explanation.
While potential explanations abound, perhaps the most intriguing is the idea that the gamma rays may be emitted by dark matter. In most models of dark matter (the mysterious, invisible form of matter that makes up over 80% of the mass of the universe), the dark matter particles can occasionally interact. When they do, they annihilate each other in a flash of gamma rays.
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This interaction only happens very, very rarely. But models of dark matter predict a whole bunch of the stuff in the cores of galaxies. Enough that it could light up in gamma rays.
Recently, a team of researchers have refined this model of dark matter and compared it to more mundane explanations, like an extra population of cosmic rays creating the excess gamma rays.
“The analysis methodology used,” explains Mattia di Mauro, a researcher at the Turin division of the National Institute for Nuclear Physics and lead author on the new study, “has provided very relevant information about the spatial distribution of excess gamma radiation, which can explain what generates the excess of high-energy photons in the Galactic center.
If the excess was, for example, caused by the interaction between cosmic rays and atoms, we would expect to observe its greater spatial distribution at lower energies and its lower diffusion at higher energies due to the propagations of cosmic particles. My study, on the other hand, underlines how spatial distribution of the excess does not change as a function of energy. This aspect had never been observed before and could be explained by dark matter presence dark matter interpretation. This is because we think the particles composing the dark matter halo should have similar energies. The analysis clearly shows that the excess of gamma rays is concentrated in the Galactic center, exactly what we would expect to find in the heart of the Milky Way if dark matter is in fact a new kind of particle.”
The result is far from conclusive, however. While dark matter models can be coerced to explain the excess, astronomers would need independent verification of this idea before accepting it.