(ed.). Gravitational waves (IOP, 2001)(422s).

Expected gravitational-wave results from LISA 143Figure 10.12. Cumulative weekly S/N ratios during the last year before MBH–MBHcoalescence at z = 1. Both the instrumental noise and the estimated binary confusionnoise are included.figure 10.11 is the accumulated S/N ratio after the first week, the second week,etc, up until the end of the year. The large jump in the last week or so, in all butthe 500M ⊙ case, is due to the frequency of the signal having swept up to wherethe LISA sensitivity is much higher.It is clear by extrapolating roughly from figures 10.11 and 10.12 that MBH–MBH coalescences resulting from structure mergers could be seen clearly even atredshifts of 10 for 10 7 M ⊙ MBHs and 20 or more for less massive ones. Thus,any such events at any plausible occurrence time will be observable. Particularlybecause of the large uncertainties concerning what happens for roughly 10 6 M ⊙or smaller MBHs after mergers of structures, the event rate for LISA apparentlycould range from less than one per decade to quite a large value.10.2.5 Fundamental physics tests with LISAOf similar importance to the astrophysical questions about MBHs discussed inthe last three sections is the fundamental physics question of whether Einstein’sgeneral relativity theory is correct. Very strong tests of the theory can be providedeither by MBH–MBH coalescences with high S/N ratio, if they are observed,or by highly unequal mass coalescences of 5 or 10M ⊙ black holes with MBHsin galactic centres. Only the latter case will be discussed here, since the muchlarger number of orbital periods observable and the substantial orbit eccentricityexpected are likely to be more important for testing relativity than a higher S/Nratio.