  If MACHOs are black holes of mass about 0.5 solar mass, they must have been
formed in the early universe when the temperature was about 1 GeV. We estimate
that in this case in our galaxy's halo out to about 50kpc there exist about
half billion black hole binaries whose coalescence times are comparable to the
age of the universe, so that the coalescence rate will be about five hundredth
events/year/galaxy. This suggests that we can expect a few events/year within
15Mpc. The gravitational waves from such coalescing black hole MACHOs can be
detected by the first generation of interferometers in the LIGO/VIRGO/TAMA/GEO
network. Therefore, the existence of black hole MACHOs can be tested within the
next five years by gravitational waves.
