  The possibility that Galactic halo MACHOs are white dwarfs has recently
attracted much attention. Using the known properties of white dwarf binaries in
the Galactic disk as a model, we estimate the possible contribution of halo
white dwarf binaries to the low-frequency (10^{-5} Hz} < f < 10^{-1}Hz)
gravitational wave background. Assuming the fraction of white dwarfs in
binaries is the same in the halo as in the disk, we find the confusion
background from halo white dwarf binaries could be five times stronger than the
expected contribution from Galactic disk binaries, dominating the response of
the proposed space based interferometer LISA. Low-frequency gravitational wave
observations will be the key to discovering the nature of the dark MACHO binary
population.
