Pablo Laguna Center for Relativistic Astrophysics School of Physics Georgia Tech, Atlanta, USA

Transcription

1 Pablo Laguna Center for Relativistic Astrophysics School of Physics Georgia Tech, Atlanta, USA

2 The Transient Sky SN, GRBs, AGN or TDEs? Arcavi et al. 2014, ApJ, 793, 38 van Velzen et al. 2011, ApJ, 741, 73 If TDEs, we will learn about t-5/3 Demographics of MBHs in quiescent galaxies Constraints on low mass galaxies hosting MBHs Growth of MBHs by accreting gas at supereddington rates Stellar dynamics in the neighborhood of MBH

3 Tidal Forces Star Black Hole Orbital Plane GmM * = GmM h 2 R * (R t R * ) GmM h 2 (R t + R * ) GmM hr * 2 3 R t Stretching along the orbital plane Compression perpendicular to the orbital plane M * R M hr * 2 3 * R t R t R * M h M * 1/3 Tidal Radius

4 Tidal Radius and Penetration Factor Star Black Hole Orbital Plane R t R t = R * β R t R p M h M * 1/3 Tidal Radius Penetration Factor Main Sequence White Dwarf R t 47 M bh R ms R M ms M 1/3 M bh 10 6 M 2/3 R t R! 22 wd M bh 0.95 R M wd M 1/3 M bh 10 4 M 2/3

5 Triangle of Astrophysical Relevance Tidal Radius R t R * M h M * 1/3 Penetration Factor β(r p ) R t R p = R * R p β t = β(r t ) = 1 β * = β(r * ) = β g = β(r g ) = M h M * M h M * 1/3 R * G M * / c 2 1/3 M h M * β 2/ Star Enters BH TDEs BH Enters Star β =(M h /M ) 1/3 β g = (M h /M ) 2/3 β t =1 No Disruption M h /M Luminet & Pichon (1989)

6 The Disruption of a Star: What to Look For Injection Fallback & Disk Formation Disruption & Compression Ejecta Near periapsis, the star disrupts and compresses. Detonation, multiple bounces, and gravitational waves are possible outcomes. Fallback material yields an accretion disk (soft x-rays), with super-eddignton outflows (optical/uv) and relativistic jets (radio/x-rays) Unbound material could also yield emission lines if irradiated by the disk

7 TDE: The Capture Loss Cone: Set of orbital directions that leads to capture or disruption Event rate depends on how the Loss Cone gets populated Stars enter the Loss Cone via collisions with other stars or relaxation Stars can also be ejected from the Loss Cone via collisions. Freitag & Benz L L LC 2G M h R LC Event rate ~ 10-4 yr -1 If R LC R h G M h σ 2 If R LC R t R * M h M * star is captured 1/3 star is disrupted

8 Tidal Compression Star Black Hole Orbital Plane ρ max ~ ρ * β 3 T max ~ T * β 2 Carter & Luminet 1993 Rosswog, Ramirez-Ruiz, Hix Haas, Shcherbakov, Bode, PL

9 Multiple Tidal Compression Luminet & Marck, 1985, MNRAS, 212, 57 β = 1 β = 5 β = 10 Multiple maximum compression a GR effect In Newtonian limit, only one compression always after periastron passage Laguna, Miller, Zurek & Davies 1993, ApJL 410, 83

10 Fallback Material!M = dm dε dε dt dε dt if dm dε const Recall ~ M bh a P a 3/2 ε ~ P 2/3 dε dt t 5/3 L M t 5/3 Rees 1988

11 The TDE Smoking Gun L M t 5/3 Evans and Kochanek 89

12 Deviations from Not included: BH and stellar spin GR Partial disruption Guillochon et al

13 Circularization & Disk Formation Relativistic precession could also assist in circularizing the bound debris. Bonnerot et al Circularization depends on the efficiency of radiative cooling. Hayasaki, Stone & Loeb

14 TDE Candidates Gezari et al PS1-10jh van Velzen et al. 2011, ApJ, 741, 73

15 Where is the emission produced? Flare: From self-intersection Prompt accretion Power-law decay: From the disk? Direct accretion?

16 White Dwarf TD Ṁ (M yr 1 ) B6S0 B6Su B6Sd B6Si B6Sa B8Sa t 5/ time after disruption (s) Haas et al 2012 WD disrupted by a 1,000 M solar BH Eventually fallback rate settles down to t -5/3 Amplitude of accretion depends on spin and its orientation

17 Effects of spin misalignment Aligned spin Spin in plane Material is influenced by frame dragging Inner region obscured by debris

18 Density & Max Compression Maximum Density β = 4 Maximum Density β = ρ max [M h -2 ] ρ max [M h -2 ] 1e-05 a/m h = 0.6 a/m h = 0.3 a/m h = 0.0 a/m h = -0.3 a/m h = e-05 a/m h = 0.6 a/m h = 0.3 a/m h = 0.0 a/m h = -0.3 a/m h = t [sec] t [sec]

19 Accretion Rates Mh(M yr 1 ) Mh(M yr 1 ) t(s) β 10 S 0 M 0.57 β 10 S 0.65 M 0.57 β 10 S 0.65 M 0.57 β 15 S 0 M 0.57 β 15 S 0.65 M 0.57 β 15 S 0.65 M 0.57 Time to swallow the bound debris: ln L T * 0.5 M ~ 5hrs M yr t -5/3 Simulation time ~ 0.6 hrs ln t (hrs)

20 Gravitational Waves from Star-BH 20 Kpc Haas, Bode, Schervakov & PL 2004 h ~ M M * h ~ β D 1 R 1 * M 4/3 2/3 * M h DR p β ~ D Mpc β ~ D Mpc 1 1 R ms R R wd R 1 1 M ms M M wd M 4/3 4/3 M h 10 6 M M h 10 4 M 2/3 2/3 f ~ M bh R p 3 ~ 0.02 β 10 ~ 10 β 10 3/2 1/2 3/2 ~ β 3/2 R * 3/2 M * 1/2 R wd R R ms R 3/2 3/2 M ms M M wd M 1/2 1/2 Hz Hz

21 Gravitational Waves from Star Compression Star Black Hole Orbital Plane Guillichon et al 2008; Stone et al 2012 h ~ β 3 M * 2 D R * β ~ β ~ D 100 Mpc D 100 Mpc 1 1 R ms R R wd R 1 1 M ms M M wd M 2 2 f ~ β 4 R * 3/2 M * 1/2 ~ 0.02 β 10 ~ 10 β R wd R R ms R 3/2 3/2 M ms M M wd M 1/2 1/2 Hz Hz

22 Summary Ø For ultra-close encounters (R t ~ R g), the tools of numerical relativity are needed to get the correct gas dynamics to model TDEs Ø Early accretion, outflow and fallback rate will tell us about the BH s spin Ø TDEs with prompt accretion will help identifying IMBH Ø Magnetic fields could provided models of jetted TDEs Ø TDEs of WD by IMBH could potentially be candidates for multi-messenger observations

23 Questions What is the physics needed in TDE simulations to understand the observed luminosities beyond the estimates from accretion rates? Are there other ubiquitous signatures of TDEs besides the t -5/3 accretion rate decay. Jetted TDEs?