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Probing Dormant M assive Black Hole Binaries at Galactic Nuclei

Probing Strong Gravity Near BHs 15-18 Feb., 2010. Probing Dormant M assive Black Hole Binaries at Galactic Nuclei. Fukun Liu Astronomy Department & KIAA, Peking University, Beijing, China.

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Probing Dormant M assive Black Hole Binaries at Galactic Nuclei

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  1. Probing Strong Gravity Near BHs 15-18 Feb., 2010 Probing Dormant Massive Black Hole Binaries at Galactic Nuclei Fukun Liu Astronomy Department & KIAA, Peking University, Beijing, China Collaborators:Xian Chen (PKU), Shuo Li (PKU),John Magorrian (Oxford),Piero Madau (UCSC), Alberto Sesana (PSU/AEI) KIAA-PKU

  2. Evolution timescale Gravitational Wave Radiation Dynamical Friction Distance ~1pc 1.1、Massiveblack hole binaries (MBHBs) and their observational evidences in gaseous environments Begelmann et al. 1980 Stefanie Komossa’ talk Most MBHBs in galactic nuclei may be quiescent: How to probe them?

  3. BH 1.2、Probing dormant MBHBs in galactic nuclei A star tidally disrupted by a massive black hole (MBH):bound part of the fluids falling back and leading transient accretion onto MBHs(Hills, 1975,Rees 1988, Phinney 1989, Evans & Kochanek 1989, Lodato et al. 2009, etc) MBH < 108M☉, rt > rg (Komossa 2004) (Komossa & Bade 1999, Halpern et al. 2004, Esquejet al.2008, Gezari et al. 2009) Spherical two-body relaxation: 10-5 yr-1 (Wang & Merritt, 2004)

  4. 2.1、Effects of MBHBs on tidal disruption rates: unbound stars Single BH Primary BH BH BH Secondary BH • Methods: (Chen, Liu, & Magorrian, 2008) • The interaction of stars and MBHBs: scattering experiments • Refilling of stars: spherical two-body relaxation 51 elliptical galaxies with known BH & bulge masses • Tidal disruption rates of unbound stars by MBHBs: ~10-7 yr-1

  5. 2.2、Effects of MBHBs on tidal disruption rates: bound stars (Chen, Madau, Sesana, Liu, 2009) N=105 • A newly formed binary surround by bound stellar cusp: • stars in chaotic region (a/3 < a* < 3a): scattering into the tidal radius of MBHs during procedure to obtain escapable velocity • stars in stable region (a* < a/3): secular periodic oscillation of eccentricity to a very high value (e* ~1) – Kozai effect The orbit of a star: a* = 1.2a, and e* = 0.5; MBH = 107M☉, q=1/81, a=ah Close-encounter cross-section: stars with a/2 < a* < 2a

  6. I • Tidal disruption rate of bound stars: • Peak rate: ~10-1 yr-1, insensitive to e or q • Very sensitive to the cusp density profile • During time: t~ 105 yr Isothermal cusp Shallower cusp • A complete picture for the stellar disruption rate in MBHBs: 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)

  7. 3. Effects of MBHBs on tidal flares: Interruption (Liu, Li, Chen, 2009, ApJL) • Numerical Simulation • Investigating the influence of MBHBs on the orbits of the tidally disrupted gas elements and their falling-back • Interaction between gas debris elements: negligible before they fall back to a few tidal radius because pressure of debris gas p  0 (Evans & Kochanek, 1989) • Debris gas returning to the tidal radius: rapid circularization (interaction/shocks) and accretion onto MBH (Rees 1988, etc) • The debris fluid elements with • agas< ab/3: stable orbits & falling back to the tidal disruption radius • agas> ab/3: chaotic & significant change on dynamical time scale

  8. Simulations: N=107 particles • Parameters: MBH=107M☉, q=mBH/MBH = 0.1, ab=104 rG • Interruption at time: Ttr ~ 0.25 Tb • Ttr/Tb:insensitive to the MBHB parameters: ab and q • Ttr/Tb ~0.15-0.5: Depending on the orbit parameters of the disrupted star • : the inclination angle between the orbital planes • : the longitude of ascending node • : the argument of pericenter

  9. 4)、Applications: preliminary results (?) X-ray flares at center of local quiescent galaxies: consistent with falling-back model (Komossa, 2004) Flare followed by extremely low upper limit: MSBHB 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) 0.4 0.0 0.8 • Chen, Liu, Magorrian 2008

  10. Conclusions • Rich electro-magnetic signature from dormant MBHBs in galactic nuclei • The tidal disruption rates of bound stars could temporarily be enhanced to ~ 0.1-1 yr-1 • The tidal disruption rates of unbound stars could be depressed to 10-7 yr-1 (~10-5 yr-1 for single MBH) • The tidal flare of stars would be interrupted by MBHBs • A quiescent MBHB (ab ~103 rg) emitting strong gravitational wave can be identified by detecting tidal flares with abrupt drop/interruption at time of a few months

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