Cosmic filaments help set first limits on dark matter's decay into gravitons - Phys.org

Physicists led by David Dunsky of New York University have proposed a novel method to search for dark matter—which makes up roughly 85% of the universe's mass—by looking for its decay into gravitons, the hypothetical particles that carry gravity, in research published in Physical Review D (2026).
Dark matter reveals itself only through gravitational effects, shaping the motion and arrangement of galaxies, but some theories suggest its particles may be slightly unstable and could gradually decay over cosmic timescales.
The approach hinges on the Gertsenshtein effect, whereby a graviton passing through a magnetic field has a small chance of converting into a detectable photon.
The team identified cosmic filaments—the vast, thread-like web connecting galaxies—as the ideal setting, since their weak magnetic fields stretch coherently across millions of light-years and fill a large portion of the observable universe.
If dark matter decayed along these filaments, it would produce a faint, steady glow of gamma-ray photons, an outcome the researchers describe as an irreducible prediction of any model allowing dark matter to decay into gravitons.
Comparing their predictions to the background gamma-ray glow measured by NASA's Fermi-LAT space telescope, the team found no unexplained excess, allowing them to set the first observational limits on dark matter's decay into gravitons.