RECOILING BLACK HOLES IN GALACTIC CENTERS Michael Boylan-Kolchin, Chung-Pei Ma, and Eliot Quataert (UC Berkeley) astro-ph/0407488
Outline • supermassive black hole binary formation and coalescence • gravitational radiation recoil • effects of recoil on stellar distributions • comparison with early-type galaxies
Supermassive Black Holes and LCDM • hierarchical cosmology + SMBH=black hole binaries • tdf << tH only for major mergers • BH coalescence rate determined by both cosmological and galactic physics: galaxy merger rate BH merger rate!
Why 1 parsec should matter to a cosmologist if ab shrinks by a factor of ~150, gravitational wave emission causes rapid coalescence How? gravitational slingshot Problem: need mass of stars …but loss cone only contains enough stars to reduce ab by a factor of ~10 (i.e. M)
Gravitational Radiation Recoil • Anisotropic emission of gravitational waves gives a “kick” to the newly-formed BH • Recoil velocity depends on BH mass ratio, BH spins, and spin alignment • Recoil velocity can reach 100-500 km/s (Favata et al. 2004) • Many consequences - Merritt et al.; Madau & Quataert; Haiman (all 2004)
Does radiation recoil have observable effects on elliptical galaxies? • Plan: use purely gravity N-Body experiments (GADGET) to study the effects of gravitational radiation recoil • simulate a kicked black hole, and follow the evolution of the stellar density and velocity profiles and trajectory of the black hole
Initial Conditions Use the equilibrium distribution function to set up the particles’ phase space coordinates: MBH=0 MBH=M*/300
Effects on the Stellar Density M*=1010 Msun, a=1 kpc: vesc=293 km/s=2.82 vcirc tdyn=26 Myr rh=0.089 a=89 pc
Long-term evolution: tdyn=26 Myr v<vesc v>vesc
No dynamical friction dynamical friction Dynamical friction enhances core formation
Additional Effects • flattened density profile core in surface brightness profile • small change of the inner velocity dispersion • effects should be largest in galaxies with smallest vcirc(a)/vesc and for largest MBH/M
So why do “power-law” ellipticals (without central cores) exist? • power-law galaxies are typically less massive than “core” ellipticals, so the effect of a kick should be more pronounced • power-law galaxies seem to host central black holes
Does gas play a role? • Faber et al. (1997): gas-rich mergers could lead to power-law galaxies • problem: requires that starburst duration is long enough to counteract both binary coalescence effects and radiation recoil effects • solution: can gas accelerate the coalescence process?
Conclusions • supermassive BHs + hierarchical cosmology = binary black holes • radiation recoil can lead to cores in stellar systems analogous to those seen in some early type galaxies • gas may play an important role in enabling binary BHs to coalesce; in turn, this may help explain the existence of power-law early-type galaxies that form hierarchically
Why 1 parsec should matter to a cosmologist BH binary must eject ~ for ab to shrink by a factor of ~150 Problem: loss cone only contains enough stars to reduce ab by a factor of ~5-10