Star-formation rate (SFR) as a function of redshift and cosmic time. The blue dashed line shows the SFR used in our previous studies, while the red line indicates the most recent update (used in this study). We note that for high redshifts (z> 2) the updated SFR generates less stars, and thus reduces formation rates of BH-BH progenitors. We marked the two highest redshift GRBs. Since GRBs form from stars or stellar remnant mergers, their positions mark the lower limit on the beginning of star formation. We also mark the detection horizon for the full advanced LIGO design sensitivity. We assume that Population II and I stars (considered in this study) form at redshifts z< 15.