A supermassive black hole growing at the center of a dark matter halo should drag the surrounding dark matter inward, creating a density spike — a steep enhancement in the dark matter concentration near the black hole. If the black hole grows adiabatically (slowly compared to the orbital timescales of the dark matter particles), the spike follows a predictable power-law profile. The Milky Way's central black hole, Sagittarius A*, should have created exactly such a spike in the dark matter distribution at the Galactic Center.
If dark matter is a thermal WIMP — a weakly interacting massive particle with an annihilation cross-section fixed by freeze-out cosmology at approximately 3×10⁻²⁶ cm³/s — then a density spike would produce a concentrated annihilation signal. More dark matter in a smaller volume means more annihilations, more gamma rays, more neutrinos. The spike turns the Galactic Center into a point source of dark matter annihilation products.
Arina, Catena, Filimonova, Fortes, and Kahlhoefer (arXiv 2602.23348, February 2026) show that the spike is not there. Fermi-LAT and MAGIC gamma-ray observations, combined with IceCube neutrino data, rule out dark matter density spikes at the Galactic Center for thermal WIMPs across a broad mass range from 10 GeV to 100 TeV. The constraints are robust: even if the photon channel constitutes only 1% of the total annihilation rate, the gamma-ray bounds still exclude steep spike profiles. Neutrino bounds independently constrain the steepest spikes in the 1-10 TeV mass range.
The thermal cross-section is not a free parameter — it is fixed by the requirement that WIMPs produce the observed dark matter abundance through freeze-out. The spike profile is not free either — it follows from adiabatic growth. The combination of fixed signal strength and fixed density enhancement leaves nowhere to hide.
Either the dark matter is not a thermal WIMP, or the spike was disrupted — by mergers, stellar scattering, or dynamical heating that erased the adiabatic prediction. The Galactic Center's silence constrains not just what dark matter is, but what happened to the space around the black hole.