Somewhere out in the vast darkness between galaxies, dark matter might be slowly dying—and scientists may have just found a new way to catch it in the act.
Dark matter is everywhere. It makes up about 85% of all the mass in the universe, yet nobody has ever seen it directly. We know it's there only because of its gravity: it tugs on stars, bends light, and shapes the way galaxies arrange themselves across the cosmos. But what actually IS dark matter? That question has puzzled physicists for decades.
Now, a team at New York University has proposed a clever new search strategy. Led by physicist David Dunsky, the group suggests hunting for dark matter by looking for its decay into gravitons—hypothetical particles thought to carry the force of gravity itself. The catch? Gravitons have never been detected either.
The researchers' idea hinges on a phenomenon called the Gertsenshtein effect. In simple terms, when a graviton passes through a magnetic field, it has a tiny chance of transforming into a photon—a particle of light. That light would be in the gamma-ray range, similar to what your body might see in a medical scan, but much fainter and coming from deep space.
So where's the best place to look? The team realized that cosmic filaments are ideal hunting grounds. These are enormous threadlike structures that connect galaxies across the universe, stretching millions of light-years through space. These filaments carry weak magnetic fields that spread across vast distances, and together they fill a large portion of the observable universe. If dark matter particles decay into gravitons along these filaments, the gravitons could then convert into photons, creating a faint cosmic glow.
To test their idea, Dunsky's team compared their predictions against real data from the Fermi-LAT space telescope, which measures gamma-rays across the entire sky. The researchers found no unexplained excess of gamma-rays coming from the filaments—which actually tells us something important. That absence of signal allowed them to set the first-ever limits on how quickly dark matter could be decaying into gravitons.
Most dark matter searches focus on the crowded center of our own galaxy, but this approach looks outward instead, at the vast web of filaments between galaxies. And unlike many proposed searches, it doesn't require any exotic new physics—the graviton-to-photon conversion is already described by known science.
Looking ahead, the team hopes a proposed new telescope called the Advanced Particle-astrophysics Telescope could sharpen these constraints tenfold. If dark matter really does decay into gravitons, this filament-scanning strategy might become our best tool yet for catching its ghostly glow.
The study was published in the journal Physical Review D.