  We propose a new mechanism by which dark matter (DM) can affect the early
universe. The hot interior of a macroscopic DM, or macro, can behave as a heat
reservoir so that energetic photons are emitted from its surface. This results
in spectral distortions (SDs) of the cosmic microwave background. The SDs
depend on the density and the cooling processes of the interior, and the
surface composition of the Macros. We use neutron stars as a model for
nuclear-density Macros and find that the spectral distortions are
mass-independent for fixed density. In our work, we find that, for Macros of
this type that constitute 100$\%$ of the dark matter, the $\mu$ and $y$
distortions can be above detection threshold for typical proposed
next-generation experiments such as PIXIE.
