Figure: A schematic dependence of the detection rate ratio on the detector sensitivity (the upper scale) and the limiting distance from which binary NS (1.4+1.4M , the middle scale) and binary BH (8.5+8.5M , the bottom scale) mergings can be detected. See the text for more detail.
Nevertheless, one may wonder whether binary BH (which are less numerous than binary NS) should always be detected more frequently than binary NS. It seems worth looking more closely on the stellar mass distribution around a GW detector on Earth (Fig. ). In this Figure, the detection rate ratio is plotted schematically against the detector sensitivity level (the upper scale), which can be expressed through the maximum distance from which binary NS/BH mergings with M and M can be detected (two bottom scales). Four segments may be distinguished in this plot (from left to right): first, when we register objects inside some part of the Galaxy, second, when all objects within the Galaxy are detected but no extragalactic objects can be detected, third, mainly extragalactic events are detected from distances more close than those at which the initial star formation occurs, and forth, where we detect all events in the Universe. In different segments different detection ratios will be obtained. In the first segment, the detection ratio depends on the galactic structure: if NS and BH populate the same spherical halo, this ratio (roman III on the vertical axis; the solid line) is if NS and BH populate the galactic disk, this ratio becomes (roman II, the bottom dashed line) if NS fill more extended halo than BH, i.e. the halo radius (roman IV, the upper dashed line), then the detection ratio is In the second and fourth segments the detection ratio will be minimal and simply equal to (roman I) In the third segment, the detection ratio of type III is realized. At the end of this segment evolutionary effects can affect the detection ratio (the dashed line).
Note that the present sensitivity of bar detectors ( ) falls within the second segment (an ``unhappy'' situation because no mass-ratio enhancement for BH detection occurs), whereas the initial laser interferometers ( ) are ``luckily'' in the third segment with the enhanced type III detection ratio. With the advanced LIGO sensitivity, it is possible to detect evolutionary effects and even reach the very edge of star formation.