The galactic center excess refers to an unexpected intensity of gamma rays emerging from the core of the Milky Way galaxy.
This view displays the entire sky at energies exceeding 1 GeV, derived from five years of data from the LAT instrument on NASA’s Fermi Gamma-ray Space Telescope. The most striking aspect is a luminous band of diffuse light along the center of the map, indicating the central plane of the Milky Way galaxy. Image credit: NASA/DOE/Fermi LAT collaboration.
Gamma rays are a form of electromagnetic radiation characterized by the shortest wavelengths and the highest energy.
The intriguing gamma-ray signal from the Milky Way’s center was initially observed in 2009 by the Large Area Telescope, the primary instrument of NASA’s Fermi Gamma-ray Space Telescope.
The source of this signal remains under discussion, with main hypotheses involving self-annihilating dark matter and undetected populations of millisecond pulsars.
“When Fermi directed its gaze toward the galaxy’s center, the outcome was unexpected,” remarked Dr. Noam Libeskind, an astrophysicist at the Leibniz Institute for Astrophysics in Potsdam.
“The telescope detected an excessive number of gamma rays, the most energetic form of light in the universe.”
“Astronomers worldwide were baffled, and numerous competing theories emerged to clarify the so-called gamma-ray excess.”
“After extensive discussion, two primary theories surfaced: either these gamma rays stem from millisecond pulsars (highly dense neutron stars rotating thousands of times per second) or from dark matter particles colliding and annihilating. Both theories, however, have their limitations.”
“Nonetheless, our findings strongly support the notion that the gamma-ray excess arises from dark matter annihilation.”
In their study, Dr. Libeskind and his team simulated the formation of the Milky Way galaxy under conditions akin to those in Earth’s neighboring universe.
They discovered that dark matter does not radiate outward from the galaxy’s core but is organized similarly to stars, suggesting that it could also contribute to the excess gamma rays.
“The Milky Way has long been recognized as existing within a spherical region filled with dark matter, often referred to as a dark matter halo,” explained Dr. Mourits Mikkel Mur, an astrophysicist at the Potsdam Leibniz Institute for Astrophysics and the University of Tartu.
“However, the degree to which this halo is aspheric or ellipsoidal remains unclear.”
“We analyzed simulations of the Milky Way and its dark matter halo and found that the flattening of this region sufficiently accounts for the gamma-ray excess due to self-annihilation of dark matter particles.”
“These calculations indicate that the search for dark matter particles capable of self-annihilation should be emphasized, bringing us closer to uncovering the enigmatic properties of these particles.”
A study of the survey results was published in this month’s edition of Physical Review Letters.
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Mikel Mur the Moor et al. 2025. Excess forms of dark matter in Fermi LAT galactic center Milky Way simulations. Physics. Pastore Rhett 135, 161005; doi: 10.1103/g9qz-h8wd
Source: www.sci.news
