  A new dynamic is identified between dark matter and nuclei. Nuclei
accelerated to MeV energies by the internal potential of composite dark matter
can undergo nuclear fusion. This effect arises in simple models of composite
dark matter made of heavy fermions bound by a light scalar field. Cosmologies
and detection prospects are explored for composites that catalyze nuclear
reactions in underground detectors and stars, including bremsstrahlung
radiation from nuclei scattering against electrons in hot plasma formed in the
composite interior. If discovered and collected, this kind of composite dark
matter could in principle serve as a ready-made, compact nuclear fusion
generator.
