  Although dark matter makes up 80% of the gravitational mass of our Galaxy,
its composition is not known. One hypothesis is that dark matter consists of
massive particles called WIMPs. WIMPs are expected to accumulate and
coannihilate in the cores of stars, but the only signature of this accumulation
has been thought to be hard- to-observe high-energy neutrinos. Here we propose
an entirely new observable signature. WIMP coannihilations in the core of a
very low-mass star, brown dwarf, or planetary-mass object should alter the
star's chemical composition via spallation reactions. Very close to the
Galactic center, these stars may acquire extremely high lithium, beryllium, and
boron abundances, even for models with otherwise- undetectable WIMP-nucleon
cross sections. These abundances should be measurable in certain stellar
systems and phenomena.
