I present a new indirect search for dark matter (DM) using hydrogen-$\alpha$ ($\mathrm{H}\alpha$) recombination emission. DM annihilation or decay products can ionize neutral gas; subsequent recombination cascades generate $\mathrm{H}\alpha$ photons through the $3\to 2$ transition. In quiet gas-rich dwarf galaxies, the $n=2$ population is negligible, so $\mathrm{H}\alpha$ is effectively unabsorbed and traces the DM-energy injection site. Using the nondetection of extended $\mathrm{H}\alpha$ emission in the Leo T dwarf galaxy with Multi Unit Spectroscopic Explorer observations, I derive the first $\mathrm{H}\alpha$-based limits on DM annihilation and decay, reaching leading sensitivity for parts of the eV–GeV mass range. Existing and upcoming telescopes can further extend this reach, establishing $\mathrm{H}\alpha$ imaging as a powerful DM search strategy.

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• Optical, UV, & IR astronomy
• Particle astrophysics
• Particle dark matter