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LSST and opportunities of PKU Astrophysics Beijing , 4 Dec. 2011. Transient activities of supermasive binary black holes in normal galactic nuclei. Fukun Liu Astronomy Department, Peking University. Collaborators

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Transient activities of supermasive binary black holes in normal galactic nuclei

LSST and opportunities of PKU Astrophysics Beijing, 4 Dec. 2011

Transient activities of supermasive binary black holes in normal galactic nuclei

Fukun Liu

Astronomy Department, Peking University


Xian Chen (PKU), Shuo Li (PKU), Xuebing Wu(PKU), John Magorrian (Oxford),Piero Madau (UCSC), Alberto Sesana (AEI), Rainer Spurzem (Heidelberg), Peter Berczik (Heidelberg)


  • 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

Formation and evolution hierarchical galaxy formation in cdm cosmology


Arp 147



Formation and evolution: hierarchical galaxy formation in CDM cosmology

Hierarchical structure formation

merge tree


Frequent galaxy interaction and mergers

If coalesce gravitational wave astronomy laser interferometer space antenna lisa danzmann 2003



If coalesce: Gravitational wave astronomy—Laser Interferometer Space Antenna (LISA) (Danzmann 2003)

LISA: 10-4-10-1 Hz (MBH104 -107M⊙)

  • —Pulsar Timing Array (PTA)

  • (Lorimer 2005)

  • very low frequency GWs

  •  10-9 — 10-5 Hz

  • MBH ~107-1010 M⊙

LISA & PTA: spatial resolution 1°,Electromagnetic counterparts are essential to Gravitational Wave detections

  • 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)

Hard Phase

Evolution timescale

gas disk?


Wave Radiation

Dynamical Friction



Hubble time

1010 yr

Silllapaa et al

Liu + Merritt &Ekers

108 yr

two AGNs

Boroson & Lauer

106 yr




Komossa et al

Komossa et al

1pc = 3.1x1018 cm

Begelmann, et al. 1980

Liu et al

SMBBHs in normal galaxies?

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



Loss cone



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)




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):

  • Constant mass distribution of plasma with specific energy (hydrodynamic simulation for =5/3 by Evans & Kochanek 1989; etc)

  • dM/d = constant

  • 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

  • Rtorus  2 Rp

Simulated accretion rate for stars with

=1.4, 1.5, 5/3, 1.8 (Lodato, King, Pringle, 2009)

  • 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 )

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).



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

  • 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)

Single BH Chandra: consistent with falling back model ~t

Primary BH

secondary BH

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 > 108 M☉

I Chandra: consistent with falling back model ~t



  • 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~ 105 yr

Isothermal cusp

Shallower cusp

  • 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 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)



  • 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 agas > amax 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 agas < amax

consist of hierarchical binary system

and its orbit changes secularly

(Mardling & Aarseth 2001):

The fluid elements with larger semimajor axis, agas > amax

do not fall back to tidal radius and BH accretion stops!

Numerical simulation of tidal accretion in SMBHB system Chandra: consistent with falling back model ~t

  • Simulations: MBH=107M☉, q=mBH/MBH = 0.1, ab=104 rG

  • Interruption at time: Ttr ~ 0.25 Tb

  • Ttr/Tb~0.15-0.5:insensitive to the MBHB parameters: ab and q

Ttr/Tb : Depending on the orbit parameters of the disrupted star

SMBBHs with orbit ab 102 rg (PTA & LISA sources): Ttr~10 days

  • 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): vrecoil  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): Vrecoil 4000 km s-1 (or  104 km/s for parabolic orbit)

Elliptical orbit e  0: increase with e

Phase I

Phase II

  • 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 II: influence radius of BH oscillation amplitude; deviation from predication with dynamic friction theory  very slow damping for much longer time

Phase I Chandra: consistent with falling back model ~t

Phase II

  • Direct N-body simulations with NAOC GPU: 106 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 MBH

x10-5 yr-1

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 (??)

flare rates vs binary fraction

  • Preliminary survey: tidal disruption candidatesin inactive galaxies (Komossa 2002, Donley et al. 2002, Gezari et al. 2006)




  • Chen, Liu, Magorrian 2008

Conclusions Chandra: consistent with falling back model ~t

  • 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