Composing some 85% of the universe’s total mass, dark matter betrays its presence only through gravity, unlike ordinary matter. Yet through new research published in Physical Review D, a team led by David Dunsky of New York University has proposed a new way to hunt for the elusive substance. Their approach involves searching for the decay of dark matter particles into gravitons: the hypothetical particles thought to carry the force of gravity itself.
Decaying dark matter
By measuring its gravitational influence on observable matter, astronomers have determined that dark matter is responsible for the motions and arrangements of galaxies. Although its true nature has eluded physicists for decades, some researchers suggest that it could be slightly unstable—with its constituent particles gradually decaying over cosmic timescales.
In their study, Dunsky’s team explored one particularly strange possibility: that dark matter particles could decay into gravitons. Much like dark matter particles, gravitons themselves have never been detected and may be almost impossible to catch directly, since gravity’s pull on individual particles is vanishingly weak.
However, some theories have predicted that gravitons may not be entirely invisible. Through a known process called the Gertsenshtein effect, a graviton passing through a magnetic field has a small chance of transforming into a photon.
Dunsky’s team realized that the best place for this to happen is in cosmic filaments: the vast web of threadlike structures connecting galaxies across the entire observable universe. These filaments carry weak yet wide-reaching magnetic fields, stretching coherently across millions of light-years, and together they fill a large share of the observable universe. If dark matter were to decay anywhere along these filaments, it could seed a faint, steady glow of gamma-ray photons.
Constraints in cosmic filaments
To test the idea, the researchers compared their predictions against real data: the background gamma-ray glow measured across the sky by the Fermi-LAT space telescope. Since no unexplained excess has been found, they used the nondetection to set the first limits on how quickly dark matter could be decaying into gravitons across an enormous range of possible dark matter masses.
Notably, the signal would come mostly from distant intergalactic filaments, rather than the crowded center of our own galaxy, where most dark matter searches usually point their instruments. Crucially, the approach doesn’t require any exotic new physics beyond the graviton-decay hypothesis itself: The light-conversion step relies on established physics.
Looking ahead, Dunsky’s team hope that a proposed successor to Fermi, the Advanced Particle-astrophysics Telescope, could sharpen these constraints by a factor of 10. If dark matter really does decay into gravitons, their filament-scanning strategy may ultimately prove to be the best tool to date for catching the glow it leaves behind.
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Publication details
David I. Dunsky et al, Observing dark matter decays to gravitons via graviton-photon conversion, Physical Review D (2026). DOI: 10.1103/yvs5-67cj
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Cosmic filaments help set first limits on dark matter’s decay into gravitons (2026, August 9)
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