The universe resembles a giant sponge: bright filaments of galaxies weave around enormous dark voids. Inside these filaments and walls hide clumps of invisible dark matter — halos. When dark matter particles collide and decay, they produce ordinary particles that telescopes can catch. But the strength of this signal depends not only on the size of the halo.
Dark matter is not spread uniformly; it clumps together like flour in dough. Small clumps within a large halo amplify the decay signal — an effect known as the boost. Previously, it was thought that the boost is the same for all halos of a given mass, regardless of their location. New research shows that the cosmic environment changes the rules of the game. Halos in filaments, walls, and voids have different concentrations and different numbers of small sub-clumps.
The scientists used simulations to calculate how the environment affects the boost. It turns out that in filaments, for light halos the signal is 15% weaker than average, while for heavy halos it is 12% stronger. In voids, the signal is always suppressed by about a third. This is similar to how the volume of a choir depends on the acoustics of the hall: the same choir sounds different in a cathedral than in an empty room.
Knowing how the environment alters the boost will help predict more precisely where to look for dark matter signals. It will also aid in modeling gravitational lenses — when massive halos bend the light of distant galaxies like eyeglass lenses. The cosmic web turns out to be not just a pretty picture but a crucial factor in the hunt for the invisible.
The cosmic web is the largest structure in the universe: its filaments stretch for hundreds of millions of light-years, and the voids between them are comparable to the distance from Earth to neighboring galaxy clusters.