Gamma-Ray Glow May Offer Clues to Dark Matter

• A new study finds that excess gamma rays near the Milky Way’s center could stem from dark matter collisions or spinning neutron stars.

Competing Theories Behind Galactic Gamma Rays

Researchers are investigating a diffuse glow of gamma rays near the center of our galaxy, which may bring science closer to confirming the existence of dark matter. While ordinary matter accounts for only 5% of the universe, dark matter is believed to make up about 27%, with the rest attributed to dark energy. Unlike visible matter, dark matter does not emit, absorb, or reflect light, making it detectable only through gravitational effects. The gamma-ray excess, mapped by NASA’s Fermi Gamma-ray Space Telescope, has prompted renewed interest in identifying its source.

Two main hypotheses have emerged to explain the observed gamma-ray emissions. One suggests they result from collisions between dark matter particles, which may annihilate and produce gamma rays. The other attributes the glow to millisecond pulsars—rapidly spinning neutron stars that emit radiation across the electromagnetic spectrum. A recent analysis using advanced simulations found both explanations equally plausible, with the dark matter model matching the observed gamma-ray patterns.

Future Observations May Provide Answers

The Cherenkov Telescope Array Observatory, currently under construction in Chile, could help distinguish between the two sources once operational, possibly by 2026. Researchers believe this ground-based gamma-ray telescope will offer the sensitivity needed to resolve the ambiguity. Lead author Moorits Mihkel Muru emphasized that despite decades of effort, no experiment has directly detected dark matter particles. The study’s findings increase the likelihood that dark matter has been indirectly observed through its gamma-ray signature.

Gamma rays have the shortest wavelengths and highest energy in the electromagnetic spectrum, making them ideal for probing high-energy cosmic phenomena. The excess was detected across a region spanning 7,000 light-years near the galactic center, roughly 26,000 light-years from Earth. According to cosmologist Joseph Silk, dark matter particles may be their own antiparticles, annihilating completely upon collision—a process that could generate gamma rays similar to those from rare proton-antiproton interactions. Alternatively, the glow could stem from thousands of previously undetected millisecond pulsars, which the Fermi satellite has confirmed as gamma-ray sources.