NASA data captures an unexplained glow in the Milky Way, and scientists think dark matter is behind it

Dark matter is estimated to make up about 27% of the universe, but not a single molecule of it has been directly detected. Perhaps until now, its existence has only been inferred by its gravitational force on visible matter. A new study suggests that the unexplained excess of far-ultraviolet light permeating the Milky Way galaxy may be the electromagnetic signature of a dark matter annihilation phenomenon, providing the first indirect glimpse into one of science’s most elusive quantities.

This research recently Journal of Cosmology and Astroparticle Physicsled by astrophysicist Michael Sekachev of the University of California, Berkeley. It focuses on axion-quark nuggets (AQNs), a particular class of dark matter candidates that are still in the hypothetical stage. These are described as ultra-dense objects smaller than a micrometer but heavier than a few grams, made up of quarks and coupled with axions, themselves still theoretical ultralight particles. What makes AQN particularly interesting is that, unlike most dark matter candidates, it can leave traces detectable through electromagnetic radiation when it interacts with ordinary matter.

brilliance without source

The mystery at the center of this research dates back nearly a decade. According to popular mechanismsNASA’s Galactic Evolution Explorer, known as GALEX, used its far-ultraviolet instrument to map the FUV background diffused across the sky, weak ultraviolet light that cannot be traced to individual, easily identified sources. In the Milky Way, most of its brightness is thought to come from starlight scattered by interstellar dust. But even after accounting for the light produced by the galaxy’s hundreds of billions of stars, astronomers were left with an excess of FUV radiation that no known source could explain.

What made this puzzle hard to ignore was its spatial nature. This excess did not match the galactic longitudes of the brightest ultraviolet-emitting stars in the Milky Way, ruling out the possibility that it was simply unresolved starlight. Its distribution is unusually smooth and even, quite different from the light emitted by stars, which tends to be much less uniform. Importantly, the brightness of GALEX’s observations matched previous data collected by NASA’s Dynamics Explorer spacecraft, which operated from a much greater distance from Earth, confirming that the signal was not due to an Earthly source or something within the solar system.

New Horizons and the Unexplored Half

Further confirmation came from an unexpected source. Observations by the ARIS ultraviolet spectrometer aboard the New Horizons spacecraft, best known for its flyby of Pluto, confirmed GALEX’s suggestion. According to the study, about half of the measured far-UV intensities could be traced back to known sources of UV radiation, while the other half remained completely unknown. That persistent, structureless residue was what drew Sekachev to the dark matter annihilation hypothesis.

After discovering that several existing theoretical models did not match the GALEX data, Sekachev turned to earlier speculative work describing electrically neutral composite dark antimatter objects, meaning that their charged internal components could still interact with normal matter. If some AQN is made of antimatter, encounters with visible matter do more than just produce radiation. They trigger annihilation events, converting mass directly into bursts of light. It is precisely this mechanism that Sekachev and his team proposed as the source of the unexplained FUV glow.

Simulations, matches, and broader implications

To test their hypothesis, the researchers turned to computer simulations. They calculated how much far-ultraviolet light would be emitted from AQN distributed according to the dark matter profile already established in certain regions of the Milky Way, including the region around our solar system. This result was consistent with both GALEX observations and New Horizons findings. As the researchers write in their paper, the goal is to “FUV electromagnetic signatures in the region around the solar system resulting from interactions between AQN and baryons”

If this model holds, the effects extend beyond ultraviolet light. The researchers found that the ionizing photons produced during these matter-antimatter annihilation events may also tell us about other unresolved astrophysical questions.

Sekachev said recent observations with the James Webb Space Telescope showed that early, faint galaxies appear to be producing surprisingly large amounts of ionizing photons, a finding that is difficult to explain with existing models. “It remains to be proven whether this is sufficient to explain the JWST results without significant changes.” he said, without making any firm claims.

This theory would also have cosmological significance beyond just the FUV puzzle. According to the study authors, AQN could help explain the matter-antimatter asymmetry of the universe and help answer why the visible and dark components of the universe exist in such similar amounts, two of the most stubborn unanswered questions in modern physics.