Transient activities of supermasive binary black holes in normal

galactic nuclei

Fukun LiuFukun LiuAstronomy Department, Peking UniversityAstronomy Department, Peking University

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

CollaboratorsXian Chen (PKU), Shuo Li (PKU), Xuebing Wu(PKU), John

Magorrian (Oxford), Piero Madau (UCSC), Alberto Sesana (AEI), Rainer Spurzem (Heidelberg), Peter Berczik (Heidelberg)

CollaboratorsXian Chen (PKU), Shuo Li (PKU), Xuebing Wu(PKU), John

Magorrian (Oxford), Piero Madau (UCSC), Alberto Sesana (AEI), Rainer Spurzem (Heidelberg), Peter Berczik (Heidelberg)

ContentContent

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: Formation and evolution: hierarchical galaxy formation hierarchical galaxy formation in in CDM cosmology

Volonteri

Hierarchical structure Hierarchical structure formationformation

Frequent galaxy interaction and mergers

merge tree

Arp 147 Arp194 Arp272

NGC2207

• If coalesceIf 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 • MBH ~107-1010 M⊙

LISA: 10-4-10-1 Hz (MBH104 -107M⊙)

Earth

Pulsar

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

0.01pc

Evolu

tion

tim

escale

Evolu

tion

tim

escale

Evolu

tion

tim

escale

Evolu

tion

tim

escale

DistanceDistanceDistanceDistance

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

1010 yr

108 yr

106 yr

1pc = 3.1x1018 cm

Hubble time

BH

MBH<108M*

rt>rg

MBH>108M*

rt<rg

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)

5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5-6.5

-6.0

-5.5

-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

Cusp galaxies Core galaxies

Sin

gle

BH

dis

rup

tion

ra

te (

yr-1)

Log MBH

3/1

*

BH*

2BH2

m

Mrr

c

GMr

t

g

starstarss

Loss coneLoss 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

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

• 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

T =2πrap 2( )

3

GMBH

⎛

⎝

⎜⎜

⎞

⎠

⎟⎟

1/2

=2−1/2π GMBH( ) −3/2

rap

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)

LEdd =1.3×10

45 M•

107 Me

⎛

⎝⎜

⎞

⎠⎟ ergs/s

Teff ;

LEdd

4πrt2σ

⎡

⎣⎢

⎤

⎦⎥

1/4

=2.4×105 r*re

⎛

⎝⎜

⎞

⎠⎟

−1/2m*

Me

⎛

⎝⎜

⎞

⎠⎟

1/6

M81/12 K

f ∝ t tflare( )

−5/3

t

flare: 1.1yr

r*

re

⎛

⎝⎜

⎞

⎠⎟

3/2m*

Me

⎛

⎝⎜

⎞

⎠⎟

−1

M81/2

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)

lg &M ∝ T Tmin( )

−5/3

UV, optical light curve of the tidal disruption flare candidate D1-9 by CFHTLS (Gezari et al. 2008).

• 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

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

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☉

Single BH

Primary BH

secondary BH

A complete picture for the stellar disruption rate in MBBHs: 3 Phases

• Phase I: shortly after MBHBs becoming bound, high rate, short Phase I: shortly after MBHBs becoming bound, high rate, short duration (Kozai timescale) duration (Kozai timescale)

• Phase II: after the initial stellar cusp is destroyed, low rate, long Phase II: after the initial stellar cusp is destroyed, low rate, long duration (until BHs coalesce) duration (until BHs coalesce)

• Phase III: after BHs coalesce, recovering, relaxation timescale Phase III: after BHs coalesce, recovering, relaxation timescale (Merritt & Wang 2005)(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~ 105 yr

Isothermal cusp

Shallower cuspI

IIIII

• 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):

ab

agas

>ab

amax

≡2.8 1+qout( )2/5

1+eb( )2/5

×

1−eb( )−6/5

1−0.3 /180°( )

The fluid elements with larger semimajor axis, agas > amax do not fall back to tidal radius and BH accretion stops ！

rap

2ab

rjb

rj∗

secular

Chaotic

• Effects on the tidal flare light curves: InterruptionEffects on the tidal flare light curves: Interruption (Liu, Li, Chen, 2009, ApJL)

lg &M ∝ T Tmin( )

−5/3

Ttr: T

orb/ 7 ~ 3yr

• 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

Numerical simulation of tidal accretion in SMBHB system

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)

=mM m+ M( )

2

• Observational signatures of recoiling black holes

Elliptical orbit e 0: increase with e

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)

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

Phase I

Phase II

X-ray flares at center of local quiescent galaxies: consistent with falling-back model (Komossa, 2004)

lg &M ∝ t−tD( ) tmin

⎡⎣ ⎤⎦−5/3

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

0.0 0.8

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

flare rates vs binary fraction

ConclusionsConclusions 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