  Data from the SDSS (300,000 galaxies) indicates that recent star formation
(within the last 1 billion years) is bimodal: half the stars form from gas with
high amounts of metals (solar metallicity), and the other half form with small
contribution of elements heavier than Helium (10-30% solar). Theoretical
studies of mass loss from the brightest stars derive significantly higher
stellar-origin BH masses (30-80 Msun) than previously estimated for sub-solar
compositions. We combine these findings to estimate the probability of
detecting gravitational waves (GWs) arising from the inspiral of double compact
objects. Our results show that a low metallicity environment significantly
boosts the formation of double compact object binaries with at least one BH. In
particular, we find the GW detection rate is increased by a factor of 20 if the
metallicity is decreased from solar (as in all previous estimates) to a 50-50
mixture of solar and 10% solar metallicity. The current sensitivity of the two
largest instruments to NS-NS binary inspirals (VIRGO: 9 Mpc; LIGO: 18) is not
high enough to ensure a first detection. However, our results indicate that if
a future instrument increased the sensitivity to 50-100 Mpc, a detection of GWs
would be expected within the first year of observation. It was previously
thought that NS-NS inspirals were the most likely source for GW detection. Our
results indicate that BH-BH binaries are 25-times more likely sources than
NS-NS systems and that we are on the cusp of GW detection.
