The Fermi telescope spent 17 years recording gamma rays from the active nuclei of galaxies with giant black holes at their centers. The glow of their jets resembles a chaotic cacophony: it constantly changes. Amid this noise, scientists found one unchanging note — at an energy of 1.5 GeV in the spectrum (i.e., the energy distribution), a narrow and absolutely stable peak appeared.
Such stability is inexplicable for jet radiation: they would have long disrupted this note. However, it fits perfectly with the dark matter hypothesis: its particles, upon colliding, turn into gamma-ray photons, and their energy equals precisely the particle mass. The detected 1.5 GeV indicates a mass slightly heavier than a proton — an unexpected coincidence, as if nature mirrored ordinary matter. This is precisely the signature Vera Rubin and Fritz Zwicky predicted half a century ago. Remarkably, the telescope was originally designed to detect explosive gamma-ray bursts, but instead captured a quiet, eternal note.
The 1.5 GeV energy roughly corresponds to the rest mass of a proton, the particles that make up atomic nuclei.
Dark matter annihilation is a favorite sci-fi trope: for example, in 'The Three-Body Problem' by Liu Cixin.