  The detection of gravitational waves (GWs) has led to a deeper understanding
of binaries of ordinary astrophysical objects, including neutron stars and
black holes. In this work, we point out that binary systems may also exist in a
dark sector with astrophysical-mass macroscopic dark matter. These "dark
binaries," when coupled to an additional attractive long-range dark force, may
generate a stochastic gravitational wave background (SGWB) with a
characteristic spectrum different from ordinary binaries. We find that the SGWB
from planet-mass dark binaries is detectable by space- and ground-based GW
observatories. The contribution to the SGWB today is smaller from binaries that
merge before recombination than after, avoiding constraints on extra radiation
degrees of freedom while potentially leaving a detectable GW signal at high
frequencies up to tens of GHz.
