List of Figures

View Image Figure 1:
20 cm VLA image of the radio source 3C 75 in the cluster of galaxies Abell 400. The image consists of two, twin-jet radio sources associated with each of two elliptical galaxies. The jets bend and appear to be interacting. The projected separation of the radio cores is about 7 kpc. Image courtesy of NRAO/AUI and F. N. Owen et al.
View Image Figure 2:
Chandra X-ray image of the starburst galaxy NGC 6240, showing the two nuclear sources. Projected separation of the nuclei is about 1.4 kpc. Image courtesy of NASA/CXC/MPE/S. Komossa et al.
View Image Figure 3:
A crude illustration of the parameter space for a SBH-IBH binary at the Galactic center. Assuming a circular orbit around a SBH of 6 3× 10 Mo ., a IBH with mass MIBH and semi-major axis a can be ruled out by measurement of an astrometric wobble of the radio image of Sgr A*. The shaded regions show the detection thresholds for astrometric resolutions of 0.01, 0.1 and 1 milliarcseconds, respectively, assuming a monitoring period of 10 years. The dashed lines indicate coalescence due to gravitational radiation in 6 10 and 7 10 years, respectively (From [84], see also [229]).
View Image Figure 4:
Distribution of field star velocity changes for a set of scattering experiments in which the field star’s velocity at infinity relative to the binary was vf0 = 0.5Vbin^ex. The binary’s mass ratio was 1:1, and the orientation of the binary’s orbital plane with respect to the x-axis was varied randomly between the scattering experiments. Each plot represents 5× 104 scattering experiments within some range of impact parameters [p1,p2] in units of a. (a) [6,10] (b) [2,4] (c) [0.6,1] (d) [0.4,0.6]. Solid lines in (a) and (b) are the distributions corresponding to scattering off a point-mass perturber. In (c) and (d), the mean of this distribution (which is very narrow) is indicated by the arrows. The gravitational slingshot is apparent in the rightward shift of the dv values when p is small, due to the randomization of ejection angles (from [133]).
View Image Figure 5:
Mass ejected by a decaying binary, in units of m12 = m1 + m2 (solid lines) or m2 (dashed lines), calculated by an integration of Equation (24View Equation), with the coefficient J(a) taken from [177]. Curves show mass that must be ejected in order for the binary to reach a separation where the emission of gravitational radiation causes coalescence on a time scale of 1010yr (lower), 109yr (middle) and 8 10 yr (upper).
View Image Figure 6:
(a) Slices of the density N (E, R,t) at one, arbitrary E, recorded, from left to right, at 100, 101, 102, 103, and 104Myr (solid curve). Initially, N (E,R, t) = 0 for R < Rlc and N (E, R,t) = const for R > Rlc. We also show the equilibrium solution of Equation (31View Equation) (dot-dashed curve). (b) The total number of stars consumed by the loss cone as a function of time (solid curve). The scale has been set to galaxy M32 with initial separation between the MBHs of 0.1pc. (From [152])
View Image Figure 7:
Final density profiles from a set of 10:1 merger simulations in which each galaxy contained a black hole (a-d) and in which neither galaxy contained a black hole (e-g) [136]. The four thin curves in each frame correspond to four different pre-merger orbits. (a), (e) Space density of stars initially associated with the secondary galaxy; thick curves are the initial density profile. (b), (f) Space density of stars initially associated with the primary galaxy; thick curves are the initial density profile. (c), (g) Space density of all stars. Lower thick curves are the initial density profile of the primary galaxy, and upper thick curves are the superposition of the initial density profiles of the primary and secondary galaxies. Lines of logarithmic slope -1 and -2 are also shown. (d), (h) Logarithmic slope of the surface density profiles of the merger remnants. Thick curves correspond to the initial primary galaxy.
View Image Figure 8:
Lagrangian radii around each of the two SBH particles in an equal-mass merger simulation [150]. From bottom to top, the radii enclose -4 10, -3.5 10, -3 10, - 2.5 10, -2 10, -1.5 10 and 10- 1 in units of the mass of one galaxy before the merger. The binary becomes “hard” at t ~~ 11, and very rapidly heats the surrounding stellar fluid, lowering the local density.
View Image Figure 9:
Evolution of the binary semi-major axis (a) and hardening rate (b) in a set of high accuracy N-body simulations; the initial galaxy model was a low-central-density Plummer sphere [20]. Units are G = Mgal = 1, E = - 1/4, with E the total energy. (a) Dashed lines are simulations with binary mass M1 = M2 = 0.005 and solid lines are for M1 = M2 = 0.02, in units where the total galaxy mass is one. (b) Filled (open) circles are for M = M = 0.005 1 2 (0.02). Crosses indicate the hardening rate predicted by a simple model in which the supply of stars to the binary is limited by the rate at which they can be scattered into the binary’s influence sphere by gravitational encounters. The simulations with largest (M1, M2) exhibit the nearly N - 1 dependence expected in the “empty loss cone” regime that is characteristic of real galaxies.
View Image Figure 10:
Results from a set of N-body integrations of a massive binary in a galaxy with a r ~ r -0.5 density cusp [205]. Each curve is the average of a set of integrations starting from different random realizations of the same initial conditions. (a) Evolution of the “mass deficit” (Equation 43View Equation), i.e. the mass in stars ejected by the binary. For a given value of binary separation a, the mass deficit is nearly independent of particle number N, implying that one can draw conclusions from observed mass deficits about the binary that produced them. (b) Evolution of binary eccentricity. The eccentricity evolution is strongly N-dependent and tends to decrease with increasing N, suggesting that the eccentricity evolution in real binaries would be modest.
View Image Figure 11:
Observed surface brightness profile of NGC 3348. The dashed line is the best-fitting Sersic model to the large-radius data. Solid line is the fit of an alternative model, the “core-Sersic” model, which fits both the inner and outer data well. The mass deficit is illustrated by the area designated “depleted zone” and the corresponding mass is roughly 3 × 108Mo . [76].
View Image Figure 12:
Effect on the nuclear density profile of SBH ejection. The initial galaxy model (black line) has a r ~ r-1 density cusp. (a) Impulsive removal of the SBH. Tick marks show the radius of the black hole’s sphere of influence rinfl before ejection. A core forms with radius ~ 2rinfl. (b) Ejection at velocities less than escape velocity. The black hole has mass 0.3% that of the galaxy; the galaxy is initially spherical and the black hole’s orbit remains nearly radial as it decays via dynamical friction. The arrow in this panel marks rinfl in the initial galaxy. [140].
View Image Figure 13:
Final spin ^a of a remnant black hole in terms of its original spin, for mass ratios q = 0.1 (red), 0.3 (green) and 0.5 (blue). The change in spin was computed using the test-particle approximation for L LSO [16, 91, 227]. Upper (lower) curves correspond to prograde (retrograde) capture from the equatorial plane; dashed curves are for capture over the pole. Capture of a low-mass secondary is likely to spin down the larger hole unless the latter is slowly rotating initially. Capture of a massive secondary results in spinup unless infall is nearly retrograde or the original spin is large.
View Image Figure 14:
Steady-state spin distributions produced by successive capture from random directions at fixed mass ratio q, for q = (1/32, 1/16,1/8, 1/4,1/2). Curves were generated using Monte-Carlo experiments based on the test-particle approximation, q « 1; hence the curve for q = 1/2 should be viewed as illustrative only.