2022ApJ...929L..24L

I show that gravitational scattering of dark matter objects of mass ∼10⁴M_☉ and speeds of ∼10 km s^–1, provides the cross section per unit mass required in self-interacting dark matter models that alleviate the small-scale structure challenges to the collisionless cold dark matter model. For primordial objects of mass 10⁴M₄M_☉, moving at the velocity dispersion characteristic of dwarf galaxies, 10v₁ km s^–1, the cross section per unit mass for gravitational scattering is \sim 10\,({M}_{4}/{v}_{1}^{4})\,{\mathrm{cm}}^{2}\,{{\rm{g}}}^{-1}. The steep decline in interaction with increasing velocity explains why self-interaction is not evident in data on massive galaxies and clusters of galaxies.