2 research outputs found
Evolution of Galactic Nuclei. I. orbital evolution of IMBH
Resent observations and theoretical interpretations suggest that IMBHs
(intermediate-mass black hole) are formed in the centers of young and compact
star clusters born close to the center of their parent galaxy. Such a star
cluster would sink toward the center of the galaxy, and at the same time stars
are stripped out of the cluster by the tidal field of the parent galaxy. We
investigated the orbital evolution of the IMBH, after its parent cluster is
completely disrupted by the tidal field of the parent galaxy, by means of
large-scale N-body simulations. We constructed a model of the central region of
our galaxy, with an SMBH (supermassive black hole) and Bahcall-Wolf stellar
cusp, and placed an IMBH in a circular orbit of radius 0.086pc. The IMBH sinks
toward the SMBH through dynamical friction, but dynamical friction becomes
ineffective when the IMBH reached the radius inside which the initial stellar
mass is comparable to the IMBH mass. This is because the IMBH kicks out the
stars. This behavior is essentially the same as the loss-cone depletion
observed in simulations of massive SMBH binaries. After the evolution through
dynamical friction stalled, the eccentricity of the orbit of the IMBH goes up,
resulting in the strong reduction in the merging timescale through
gravitational wave radiation. Our result indicates that the IMBHs formed close
to the galactic center can merge with the central SMBH in short time. The
number of merging events detectable with DECIGO is estimated to be around 50
per year. Event rate for LISA would be similar or less, depending on the growth
mode of IMBHs.Comment: 12 pages, 24 figures, submitted to Ap
LISA observations of massive black hole mergers: event rates and issues in waveform modelling
The observability of gravitational waves from supermassive and
intermediate-mass black holes by the forecoming Laser Interferometer Space
Antenna (LISA), and the physics we can learn from the observations, will depend
on two basic factors: the event rates for massive black hole mergers occurring
in the LISA best sensitivity window, and our theoretical knowledge of the
gravitational waveforms. We first provide a concise review of the literature on
LISA event rates for massive black hole mergers, as predicted by different
formation scenarios. Then we discuss what (in our view) are the most urgent
issues to address in terms of waveform modelling. For massive black hole binary
inspiral these include spin precession, eccentricity, the effect of high-order
Post-Newtonian terms in the amplitude and phase, and an accurate prediction of
the transition from inspiral to plunge. For black hole ringdown, numerical
relativity will ultimately be required to determine the relative quasinormal
mode excitation, and to reduce the dimensionality of the template space in
matched filtering.Comment: 14 pages, 2 figures. Added section with conclusions and outlook.
Matches version to appear in the proceedings of 10th Annual Gravitational
Wave Data Analysis Workshop (GWDAW 10), Brownsville, Texas, 14-17 Dec 200