Cosmic-ray positrons arrive in numbers that rise where they should fall. PAMELA's 2008 measurement, confirmed and extended by AMS-02 on the space station with unprecedented statistics, shows the positron fraction climbing from 10 GeV to several hundred GeV, where secondary production, positrons made by cosmic-ray protons striking interstellar gas, predicts a smooth decline. The excess requires a primary positron source, and for years the electrifying candidate was dark matter annihilation: TeV-scale WIMPs annihilating to leptons could fit the rise. The fit demanded uncomfortable accessories, annihilation cross-sections boosted hundreds of times above the thermal relic value, leptophilic channels to evade antiproton bounds, and a spectral cutoff whose energy kept moving with the data.
The astrophysical alternative matured meanwhile: pulsars, whose magnetospheres pair-produce energetic positrons, are abundant, and the HAWC and LHAASO detections of extended TeV halos around the nearby pulsars Geminga and Monogem prove they inject high-energy leptons into the interstellar medium, with measured diffusion properties. Quantitative models with two or three nearby middle-aged pulsars reproduce the AMS-02 spectrum without exotic accessories, and the dark matter reading is further cornered by CMB energy-injection bounds excluding the required annihilation enhancement at recombination. A residual debate over local diffusion and the spectral shape's high-energy behavior keeps attribution formally open.
The standing is an anomaly largely domesticated: the positron excess is real, primary, and most economically pulsar-fed, with the dark matter interpretation surviving only in parameter corners. AMS-02's extended dataset and the anisotropy limits will close the remaining attribution gap.