RECOILING BLACK HOLES IN GALACTIC CENTERS Michael Boylan-Kolchin, Chung-Pei Ma, and Eliot Quataert (UC Berkeley) astro-ph/

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 t df << t H 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 a b shrinks by a factor of ~150, gravitational wave emission causes rapid coalescence Problem: need mass of stars …but loss cone only contains enough stars to reduce a b by a factor of ~10 (i.e. M  ) How? gravitational slingshot

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 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: M BH =0 M BH =M * /300

Effects on the Stellar Density M * =10 10 M sun, a=1 kpc: v esc =293 km/s=2.82 v circ t dyn =26 Myr r h =0.089 a=89 pc

Long-term evolution: t dyn =26 Myr v<v esc v>v esc

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 v circ (a)/v esc and for largest M BH /M

Faber et al. (1997)

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?

Escala et al. (2004)

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 a b to shrink by a factor of ~150 Problem: loss cone only contains enough stars to reduce a b by a factor of ~5-10