Data from the SDSS ( \sim 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 ( \sim 10 - 30 \% solar ) .
Theoretical studies of mass loss from the brightest stars derive significantly higher stellar-origin BH masses ( \sim 30 - 80 { ~ { } M } _ { \odot } ) 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 : \sim 9 Mpc ; LIGO : \sim 18 ) is not high enough to ensure a first detection .
However , our results indicate that if a future instrument increased the sensitivity to \sim 50 - 100 \mbox { 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 \sim 25 -times more likely sources than NS-NS systems and that we are on the cusp of GW detection .