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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.