  Cosmologies in which dark matter clumps strongly on small scales are
unfavorable to terrestrial detectors that are as yet unexposed to the clumps. I
show that sub-hectometer clumps could trigger thermonuclear runaways by
scattering on nuclei in white dwarf cores (carbon and oxygen) and neutron star
oceans (carbon), setting off Type Ia-like supernovae and x-ray superbursts
respectively. I consider two scenarios: ``dark clusters" that are essentially
microhalos, and ``long-range dark nuggets", essentially macroscopic composites,
with long-range Yukawa baryonic interactions that source the energy for
igniting explosions. I constrain dark clusters weighing between the Planck mass
and asteroid masses, and long-range dark nuggets over a wider mass range
spanning forty orders of magnitude. These limits greatly complement searches I
had co-proposed in 2109.04582 for scattering interactions of dark clumps in
neutron stars, cosmic rays, and pre-historic minerals.
