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

140 LISA: A proposed joint ESA–NASA gravitational-wave missionFigure 10.10. Expected signals from BH–MBH binaries. The instrumental and confusionnoise thresholds are shown for one year of observations, but for a S/N ratio of 10. Thedifferent symbols correspond to different MBH masses. For a given mass, the individualpoints correspond to factor of two different values of the redshift z.range in the redshift z, the signal strength and frequency of the strongest expectedsignal was calculated. The different symbols correspond to the different MBHmasses, ranging from 5 × 10 5 to 4 × 10 6 M ⊙ , and the highest and lowest valuesof z for each M are labelled. It should be noted that, only in this figure, thethreshold S/N ratio is taken to be ten rather than five. This is because the orbitsin this case generally will be quite complex because of relativistic effects, asdiscussed later, and thus require a higher S/N ratio for detection. With improvedunderstanding of the conditions in the cusps, the distribution of MBH massesfor such events may give information that cannot be obtained in other ways onthe demographics of intermediate mass black holes in galactic centres throughoutmuch of the universe.A recent paper by Miralda-Escuda and Gould [68] looks specifically at thestellar mass black holes in the cusp around the MBH in the centre of our galaxy.With assumed masses of 0.7M ⊙ for stars in the cusp and 7M ⊙ for the black holes,and with 1% of the mass in the black holes, they show that the black holes willrapidly sink down closer to the center. With this model, they estimate that about24 000 black holes would be concentrated within 0.7 parsec of the MBH, andcalculate a lifetime for loss of the black holes to the MBH of about 3×10 10 years.If a substantial fraction of the black holes approach coalescence gradually, andwith many galaxies like ours in the universe, the possible LISA event rate fromthis study also may be considerable. On the other hand, the authors suggest thatmost of the stars in the inner few parsecs of the cusp would be forced out to larger