Milky Way shows excess gamma rays due to dark matter annihilation, study suggests

New research shows that the distribution of dark matter in our galaxy is different than previously thought, reinforcing dark matter’s status as a potential source of the excess gamma rays observed at the center of the Milky Way. High-resolution simulations reveal that the distribution of dark matter in the inner galaxy is not spherical, but flattened and asymmetric. The results support the theory that the excess gamma rays are due to the annihilation of dark matter.

Scientists have long suspected the annihilation of dark matter to be the cause of these rays, but the spatial spread of the rays did not match the arrangement of dark matter that they had predicted. Another theory suggests that ancient millisecond pulsars could produce these rays.

For the new study published in Physical Examination LettersResearchers modeled the formation of Milky Way-like galaxies under environmental conditions similar to those in Earth’s cosmic neighborhood, thereby reproducing simulated Milky Way-like galaxies that closely resemble the real thing.

They found that dark matter does not radiate outward from the galactic center, but rather is organized in a similar way to stars, meaning the former could just as easily have produced the excess gamma rays.

“When the FERMI space telescope pointed toward the galactic center, the results were surprising. The telescope measured too many gamma rays, the most energetic form of light in the universe. Astronomers around the world were perplexed, and competing theories began to arise to explain so-called ‘excess gamma rays,'” says Noam Libeskind of the Institute Leibniz of Potsdam Astrophysics (AIP).

After much debate, two ideas emerged: either these gamma rays were the result of millisecond pulsars (ultra-dense neutron stars that rotate thousands of times per second), or dark matter particles crashing into each other and annihilating each other. Both theories have their drawbacks. However, new results proposed by AIP scientists in collaboration with the Hebrew University of Israel and Johns Hopkins University in the United States have shed new light on this problem, effectively confirming the theory that the excess gamma rays are due to the annihilation of dark matter.

The Milky Way has long been known to live in what is called a dark matter halo, a spherical region filled with dark matter around it. However, the extent to which this halo is aspherical or ellipsoidal has not been appreciated.

Moorits Muru, lead author of the paper, says: “We analyzed simulations of the Milky Way and its dark matter halo and found that the flattening of this region is sufficient to explain the excess gamma rays as being due to the self-annihilation of dark matter particles. These calculations demonstrate that the hunt for dark matter particles (which can self-annihilate) should be encouraged and bring us closer to understanding the mysterious nature of these particles.