Scientists Close In on Dark Matter Using Gamma Rays in the Milky Way

Researchers may be approaching a breakthrough in confirming the existence of dark matter, the invisible substance thought to make up 27% of the universe, as they study a diffuse glow of gamma rays near the center of the Milky Way.

Ordinary matter—everything from stars to planets and people—accounts for only about 5% of the cosmos, while dark energy makes up the remaining roughly 68%. Dark matter cannot emit, absorb, or reflect light, making it notoriously difficult to detect directly.

The glow of gamma rays, mapped by NASA’s Fermi Gamma-ray Space Telescope, has sparked interest as a potential signature of colliding dark matter particles. However, another plausible explanation is that the gamma rays are emitted by millisecond pulsars, dense neutron stars spinning hundreds of times per second.

A new study in Physical Review Letters analyzed these competing hypotheses using advanced simulations and found that dark matter fits the observed gamma-ray data at least as well as the pulsar theory, increasing the odds that dark matter has been indirectly observed.

"Understanding the nature of dark matter is one of the greatest problems in physics," said cosmologist Joseph Silk of Johns Hopkins University and Sorbonne University. "Our analysis shows dark matter could explain these gamma-ray signals as well as neutron stars."

The Cherenkov Telescope Array Observatory in Chile, set to become operational around 2026, may be able to distinguish between the two sources of gamma rays and provide more definitive evidence.

The gamma-ray excess spans the innermost 7,000 light-years of the galaxy, about 26,000 light-years from Earth. If caused by dark matter, the gamma rays would be produced as particles collide and annihilate each other—a process unique to certain dark matter candidates.

"Dark matter particles are thought to be their own antiparticles, annihilating when they collide, producing energetic gamma rays," explained Silk. "This phenomenon is distinct from any other known source."

While the mystery remains unresolved, the findings offer a promising path toward detecting one of the universe’s most elusive components.