1. Transient activities of supermasive binary black holes in normal galactic nuclei Fukun Liu Astronomy Department, Peking University LSST and opportunities of PKU Astrophysics Beijing, 4 Dec. 2011 Collaborators Xian Chen (PKU), Shuo Li (PKU), Xuebing Wu(PKU), John Magorrian (Oxford), Piero Madau (UCSC), Alberto Sesana (AEI), Rainer Spurzem (Heidelberg), Peter Berczik (Heidelberg) Collaborators Xian Chen (PKU), Shuo Li (PKU), Xuebing Wu(PKU), John Magorrian (Oxford), Piero Madau (UCSC), Alberto Sesana (AEI), Rainer Spurzem (Heidelberg), Peter Berczik (Heidelberg)

2. Content   The formation and evolution of supermassive black hole binaries (SMBHBs)   Transient activity of supermassive black hole in galactic nuclei   Tidal disruption of stars in SMBHBs in galactic nuclei: rate and light curves   Tidal disruption of stars by gravitational recoiling SMBHs   Conclusions

3. Formation and evolution: hierarchical galaxy formation in Formation and evolution: hierarchical galaxy formation in  CDM cosmology Volonteri Hierarchical structure formation Frequent galaxy interaction and mergers merge tree Arp 147 Arp194 Arp272 NGC2207

4. If coalesce If coalesce: Gravitational wave astronomy —Laser Interferometer Space Antenna (LISA) (Danzmann 2003) —Pulsar Timing Array (PTA) (Lorimer 2005) very low frequency GWs  10 -9 — 10 -5 Hz M BH ~10 7 -10 10 M ⊙ LISA:  10 -4 -10 -1 Hz (M BH  10 4 -10 7 M ⊙ ) Earth Pulsar Electromagnetic counterparts are essential to Gravitational Wave detections LISA & PTA: spatial resolution   1 °, Electromagnetic counterparts are essential to Gravitational Wave detections

5. 0.01pc Evolution timescale DistanceDistance Hard Phase Dynamical Friction Gravitational Wave Radiation Begelmann, et al. 1980 ~1pc Evolution of MBBHs and observational evidences (Begelman et al. 1980; Sillapaa et al. 1988; Komossa et al. 2003, 2008; Liu, Wu, Cao 2003; Liu 2004; Liu, X., et al. 2009,2010) gas disk? two AGNs Komossa et al Boroson & Lauer Liu + Merritt &Ekers Silllapaa et al Komossa et al Liu et al SMBBHs in normal galaxies? 100pc1pc 10 10 yr 10 8 yr 10 6 yr 1pc = 3.1x10 18 cm Hubble time

6. BH M BH <10 8 M * r t >r g M BH >10 8 M * r t <r g Stellar disruption rate~10 -5 yr -1 (Wang & Merritt, 2004), enhanced due to non- spherical (~2), tri-axial (~10-100), or galaxy mergers (Chen Xian’s talk) stars Loss cone A dormant SMBH is temporarily activated by tidally disrupting a star ( Hills 1975; Rees 1988; Phinney 1989; Evans & Kochanek 1989; Komossa et al. 2004; Lodato et al. 2009; Strubbe & Quataert 2009; Kasen & Ramirez-Ruiz 2010; etc ): γ-ray, X-ray, UV, optical, Radio; LSST surveys Stellar tidal disruption by SMBHs in local galactic nuclei

7. Tidal accretion: falling back model (Rees 1988, Phinney 1988) The tidal gas debris with  < 0 moves with a Keplerian orbit and return to tidal radius after a Keplerian time Assumptions (Rees 1988): 1.Constant mass distribution of plasma with specific energy ( hydrodynamic simulation for  =5/3 by Evans & Kochanek 1989; etc ) dM/d  = constant 2.Once returning to the pericenter, the material rapidly loses its angular momentum due to strong shocks at several tidal radii and circularizes to form an orbiting torus at R torus  2 R p RpRp Simulated accretion rate for stars with  =1.4, 1.5, 5/3, 1.8 (Lodato, King, Pringle, 2009)

8. Observations of tidal flares: consistent with falling back model (Rees, 1988): accretion disk and jets Initially radiating with Eddington luminosity: Thermal spectrum of effective temperature Decaying after peak as power- law with time on a timescale: RX J 1242.6-1119A (Komossa et al. 2004) Tidal accretion and jet in SW 1644+57 (Bloom et al. 2011, Zauderer et al. 2011 )

9. Tidal X-ray flares at center of NGC 5905 by ROSAT and Chandra: consistent with falling back model ~t -5/3 (Halpern, Gezari, Komossa, 2004, ApJ) UV, optical light curve of the tidal disruption flare candidate D1-9 by CFHTLS (Gezari et al. 2008).

10. Cusp destruction of bright galaxy (Merritt 2006) hyper-velocity stars in Milk Way (Yu, et al 2003) Hyper-velocity binary stars (Lu, Yu, Lin, 2007) BH Effects of SMBHBs on tidal disruption rates Unbound stars ( Chen, Liu, & Magorrian, 2008 ) and bound stars ( Chen, Madau, Sesana, Liu, 2009; Chen, Sesana, Madau, Liu, 2011 ): Interaction of stars and MBHBs: scattering experiments Three-body Sling-shot effects: ejecting most of the stars (Quilan, 1996): decreasing the tidal disruption rates of unbound stars

11. Disruption rates of unbound stars in spherical two-body relaxation (Chen, Liu, Magorrian, 2008, ApJ) 51 elliptical galaxies: solar type stars Tidal disruption rates of unbound stars by SMBHBs: ~10 -7 yr -1 Possible tidal flares in SMBHBs with mass > 10 8 M ☉ Single BH Primary BH secondary BH

12. A complete picture for the stellar disruption rate in MBBHs: 3 Phases Phase I: shortly after MBHBs becoming bound, high rate, short duration (Kozai timescale)Phase I: shortly after MBHBs becoming bound, high rate, short duration (Kozai timescale) Phase II: after the initial stellar cusp is destroyed, low rate, long duration (until BHs coalesce) Phase II: after the initial stellar cusp is destroyed, low rate, long duration (until BHs coalesce) Phase III: after BHs coalesce, recovering, relaxation timescale (Merritt & Wang 2005) Phase III: after BHs coalesce, recovering, relaxation timescale (Merritt & Wang 2005) Tidal disruption rate of bound stars: Peak rate: ~10 -1 yr -1, insensitive to e or q Very sensitive to the cusp density profile of galaxies During time: t~ 10 5 yr Isothermal cusp Shallower cusp I II III

13. binary black holes and gas debris consist of a restricted three-body system gas-debris with large bind energy |  | is in the secular region and fall back to tidal radius to form accretion Region with a gas > a max are chaotic and fluid elements exchange angular momentum with binary BH on dynamical time scale, For a restricted three-body system, the fluid elements with a gas < a max consist of hierarchical binary system and its orbit changes secularly (Mardling & Aarseth 2001):  The fluid elements with larger semimajor axis, a gas > a max do not fall back to tidal radius and BH accretion stops ！ 2a b  secular Chaotic Effects on the tidal flare light curves: InterruptionEffects on the tidal flare light curves: Interruption (Liu, Li, Chen, 2009, ApJL)

14. Simulations: M BH =10 7 M ☉, q=m BH /M BH = 0.1, a b =10 4 r G Interruption at time: T tr ~ 0.25 T b T tr /T b ~0.15-0.5 : insensitive to the MBHB parameters: a b and q T tr / T b : Depending on the orbit parameters of the disrupted star SMBBHs with orbit a b  10 2 r g (PTA & LISA sources): T tr ~10 days Numerical simulation of tidal accretion in SMBHB system

15.   SMBHBs get merged due to interaction with stars or gas disk   Any asymmetry in the merging binary system (mass differences, BH spins) leads to anisotropic gravitational radiation ( Peres 1962; Berkenstein 1973 ): carrying away momentum  recoil velocity  Schwarzschild SMBHBs: unequal masses ( Fitchett 1983; Favata et al. 2004; Baker et al. 2006; Gonzalez et al. 2007; etc): v recoil  176 km s -1 (symmetric mass  = 0.195)  Kerr SMBHBs due to BH spins ( Campanelli et al. 2007a,b; Herrmann et al. 2007; Koppitz et al. 2007; Pollney et al. 2007; Rezzolla, et al. 2008 ): V recoil  4000 km s -1 (or  10 4 km/s for parabolic orbit) Observational signatures of recoiling black holes Elliptical orbit e  0: increase with e

16.  The dynamic evolution of a kicked SMBH in galaxy: two oscillation phases (Phases I & II) + Brownian motion (Phase III) Phase I: influence radius of BH  oscillation amplitude; as predication with dynamic friction theory  damping on dynamic friction timescale Phase I Phase II Phase II: influence radius of BH  oscillation amplitude; deviation from predication with dynamic friction theory  very slow damping for much longer time Post-merger: recoiling MBHs in galaxies:Post-merger: recoiling MBHs in galaxies: N-body simulations (Li, Liu, Berczik, Chen, Spurzem, 2011, ApJ)

17. Direct N-body simulations with NAOC GPU: 10 6 particles Recoiling MBHs: ejecting and oscillating in galaxies: two phases Off-nucleus tidal stellar disruption:  10 -6 yr - 1 (consistent with Komossa & Merritt 2008) Off-nuclear massive compact stellar global cluster M * ~10 -3 M BH x10 -5 yr -1 Phase I Phase II

18. X-ray flares at center of local quiescent galaxies: consistent with falling-back model (Komossa, 2004) Normal flare followed by extremely rapid disappear: SMBHB in RXJ1624+75 ( ??) SMBHBs in local galaxies? SMBHBs in local galaxies? Chen, Liu, Magorrian 2008 0.4 0.00.8 Preliminary survey: tidal disruption candidates in inactive galaxies (Komossa 2002, Donley et al. 2002, Gezari et al. 2006) flare rates vs binary fraction

19. Conclusions   SMBHBs are products of galaxy formation in CDM   SMBHBs would dramatically the change tidal disruption rate of stars in galactic nuclei: as high as ~ 0.1 galaxy -1 yr -1   SMBHBs would interrupt the tidal disruption light curves, which can be used to identify strong gravitational wave radiation system in galactic nuclei   Recoiling SMBHB in galactic nuclei may be identified by observing spatial off-nuclear tidal flare