🔭 Gamma glow at the center of the Milky Way: dark matter remains credible

For more than ten years, astronomers have observed an enigmatic gamma glow coming from the heart of our Milky Way. Known as the galactic center excess, it spans thousands of light-years and divides the scientific community. Two theories compete: pulsars (rapidly rotating neutron stars) or the annihilation of dark matter particles. A new study reignites the debate: dark matter is not yet ruled out.

To understand this glow, one must know that dark matter makes up 85% of the matter in the universe. Invisible, it interacts neither with light nor with ordinary matter. Some models propose that its particles are their own antiparticles: when two of them meet, they annihilate, producing gamma rays. This phenomenon would only occur in very dense regions, like the centers of galaxies.


The research team, led by Florian List from the University of Vienna, used machine learning to analyze more than a million simulations of gamma observations. Previous results pointed to point sources like pulsars. However, this new analysis indicates that these sources would be much fainter than previously thought, making their distinction from dark matter annihilation difficult.

In practice, while earlier studies indicated that a few hundred pulsars were enough to produce the gamma excess, the new results show that more than 35,000 would be needed. These pulsars would be so faint that they would almost resemble the expected signature of dark matter. Nick Rodd from Lawrence Berkeley National Laboratory noted that these sources become almost indistinguishable.

Despite these advances, the researchers point out that their work does not prove that dark matter is the cause. It simply shows that it is still too early to rule out this hypothesis. The origin of this gamma excess remains one of the most debated questions in astrophysics, as Florian List reminded.

The study was published in the journal Physical Review Letters. For scientists, the quest continues, and new observations, particularly with the James Webb Space Telescope, could provide additional clues. In the meantime, dark matter remains a credible candidate to explain this enigmatic glow at the center of our Galaxy.

What is dark matter?

Dark matter is a form of matter that does not emit, absorb, or reflect light, making it invisible to telescopes. It interacts with ordinary matter only through gravity. It is estimated to make up about 85% of all matter in the universe.

Its presence is inferred from gravitational effects on galaxies and galaxy clusters. For example, stars at the edges of galaxies rotate faster than visible matter alone would allow, implying additional invisible mass.

Several candidates exist for dark matter, such as WIMPs (weakly interacting massive particles) or axions. None have been directly detected yet, but research continues, particularly in underground detectors and at the LHC.

How are gamma rays produced?

Gamma rays are the most energetic form of light in the electromagnetic spectrum. They are produced during violent phenomena such as supernova explosions, pulsars, or the annihilation of matter and antimatter.

In the case of the galactic center excess, two possible sources are considered: pulsars, which are rapidly rotating neutron stars emitting gamma rays, or dark matter particles annihilating each other.

Detecting these gamma rays is difficult because Earth's atmosphere blocks them. Space telescopes like Fermi-LAT or ground-based observatories like H.E.S.S. are needed to observe them. The galactic center is a very bright and difficult region to analyze, making the analysis delicate.