Milky Way’s Galactic Center Excess is Due to Dark Matter Annihilation: Study

The Galactic Center Excess is an unexpected concentration of gamma rays emerging from the center of our Milky Way.

This view shows the entire sky at energies above 1 GeV, based on five years of data from the LAT instrument on NASA’s Fermi Gamma-ray Space Telescope; The most prominent feature is the bright band of diffuse glow along the center of the map, which marks the central plane of our Milky Way. Image credit: NASA / DOE / Fermi LAT collaboration.

Gamma rays are a form of electromagnetic radiation with the shortest wavelength and highest energy.

The anomalous gamma-ray signal from the core of the Milky Way was first detected in 2009 by the Large Area Telescope, the main instrument of NASA’s Fermi Gamma-ray Space Telescope.

Its origin has been debated, with proposed sources including self-annihilating dark matter and an undetected population of millisecond pulsars.

“When Fermi pointed to the galactic center, the results were surprising,” said Dr. Noam Libeskind, an astrophysicist at the Leibniz Institute for Astrophysics in Potsdam.

“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 flood in to explain the so-called gamma ray excess.”

“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, our results do indeed support the theory that the excess gamma rays are due to the annihilation of dark matter.”

In their study, Dr. Libeskind and his colleagues modeled the formation of Milky Way-like galaxies under environmental conditions similar to those in Earth’s cosmic neighborhood.

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.

“It has long been known that the Milky Way lives in what is called a dark matter halo, a spherical region filled with dark matter around it,” said Dr. Moorits Mihkel Muru, an astrophysicist at the Leibniz Institute for Astrophysics in Potsdam and the University of Tartu.

“However, the extent to which this halo is aspherical or ellipsoidal has not been appreciated.”

“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 – capable of self-annihilation – should be encouraged and bring us closer to understanding the mysterious nature of these particles.”

An article on the results was published this month in the journal Physical Examination Letters.

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Maurits Mihkel Muru and others. 2025. Excess dark matter morphology from the Fermi-LAT Galactic Center in Milky Way simulations. Phys. Reverend Lett 135, 161005; doi: 10.1103/g9qz-h8wd