Researchers led by Michael Sekatchev propose that axion quark nuggets (AQNs)—hypothetical ultra-dense dark-matter objects—could produce the unexplained diffuse far-ultraviolet glow observed across the Milky Way. Simulations show AQN–baryon annihilations can reproduce the intensity and smooth distribution measured by GALEX and New Horizons. The team also suggests AQNs may have implications for matter–antimatter asymmetry and for ionizing-photon budgets relevant to early galaxies observed by JWST, though further tests are needed.
Could Dark-Matter Nuggets Be Powering a Mysterious Ultraviolet Glow Across the Milky Way?
Dark Matter May Be Filling Our Galaxy With LightDrPixel - Getty Images
Dark matter remains invisible to telescopes, but a new hypothesis suggests it might leave an unexpected fingerprint: a faint, diffuse far-ultraviolet (FUV) glow across our galaxy. Researchers led by Michael Sekatchev (UC Berkeley) propose that a hypothetical form of dark matter known as axion quark nuggets (AQNs) could produce the excess FUV emission observed by missions such as GALEX and New Horizons when they interact with ordinary matter.
What Is the Puzzle?
About a decade ago, NASA’s Galaxy Evolution Explorer (GALEX) mapped the diffuse FUV background of the sky. After accounting for known sources—starlight scattered by interstellar dust and the combined emission of the Milky Way’s stars—an unexplained, smoothly distributed excess remained. Independent measurements from the earlier Dynamics Explorer and later from New Horizons’ Alice UV spectrograph corroborated that this extra component is galactic in origin, unusually uniform, and not simply unresolved starlight or a Solar System artifact.
Axion Quark Nuggets: A Dark-Matter Candidate That Shines
AQNs are a speculative class of ultra-dense objects composed of quarks and linked theoretically to axions. They would behave like cold dark matter gravitationally but, unlike many dark-matter candidates, could produce electromagnetic radiation when they encounter baryonic (ordinary) matter. If some nuggets contain antimatter, collisions would trigger annihilation events that convert mass into energetic photons—potentially including FUV light.
Modeling the Glow
Sekatchev and collaborators simulated the FUV emission expected if AQNs are distributed according to established dark-matter profiles in parts of the Milky Way. Their results reproduce key aspects of the GALEX and New Horizons measurements: the overall intensity and the unusually smooth spatial distribution. The team notes that AQNs with masses > a few grams and sub-micrometer sizes could plausibly create the observed signature when interacting with interstellar baryons.
Broader Implications
Beyond explaining the local FUV excess, the authors argue that AQNs could help address other open questions: the apparent similarity in mass densities of visible and dark matter and the universe’s matter–antimatter asymmetry. They also suggest that ionizing photons produced by AQN annihilations might contribute to the population of energetic photons seen from faint, early galaxies—an effect that could be relevant to recent James Webb Space Telescope (JWST) findings. The team is careful to emphasize that whether AQNs alone can explain these broader observations remains to be demonstrated.
Bottom line: If AQNs exist and occasionally annihilate with ordinary matter, dark matter might not be entirely silent—its interactions could produce the faint ultraviolet glow now observed across the Milky Way.
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