The Galactic Center a unique laboratory for studying massive black holes

Transcription

1 The Galactic Center a unique laboratory for studying massive black holes Reinhard Genzel MPE on behalf of the ESO Galactic Center community (MPE, MPIA, UCologne, Observatoire de Paris, Granada, MPIfR, and ESO)

2 critical observations: emission line widths VLBI infrared emission/variability an unambiguous proof for the existence of a black hole requires the determination of the gravitational field/space time metric to the scale of the event horizon.

3 A Journey to the Center of the Milky Way 6cm radio emission VLA SgrA* 1 light year ESO 1151

4 2 decades of progress in high resolution IR imaging & precision astrometry SHARP at the single 3.5m NTT speckle frame with SHARP first images 1991 Adaptive seeing limited NACO (1990) astrometric precision 5 (0.2 pc) mas 2mas 300μas limiting K-mag (log flux) 10μas SgrA* 12 AO star SINFONI speckle imaging NTT natural laser (1992) star AO IR-AO (2005/2006) (2003) ESO VLT(I): 1990 NACO/SINFONI time seeing ~ PARSEC laser time 1.5 DePoy & Sharp 1991, Eckart et al. 1993, 1995, Genzel et al. 2003, Ghez et al. 2005

5 NTT Nature 383, 1996 ( : courtesy of Harry van der Laan) 400 km/s 10 M pc 9.7 3

6 Should not be there: B-stars in the central light days with proper motions >10 3 km/s 1000 km/s 1 (0.04 pc) 10 M pc 12 3 Eckart & Genzel 1997, Genzel et al. 1997

7 Nature 419, 2002 R p =1500 R S 10 M pc 16 3 see also Ghez et al. 2003

8 Once around: S2 ( ) SINFONI + VLT M = 4.30(±0.20) stat ( 0.30) sys x10 6 M R 0 = 8.28 (±0.15) stat (±0.29) sys kpc ρ > M pc -3 M extended /M < a few 10-2 SgrA* Ghez et al. 2008, Gillessen et al. 2009a,b

9 The environment of a massive black hole key theoretical predictions: star formation near BH very difficult if not impossible power-law cusp of old stars & remnants centered on BH L SgrA* ~ L binaries on loss cone orbits get captured with one member ejected out of Galaxy

10 Young massive stars near the BH flat IMF! Nayakshin & Sunyaev 2005 Paumard et al Bartko et al light year Allen et al. 1990, Forrest et al. 1987, Krabbe et al. 1991, 1995, Gerhard 2001, Levin & Beloborodov 2003, Genzel et al. 2003, Kim et al. 2003, Portegies Zwart et al , Guerkan et al. 2005, Paumard et al. 2006, Martins et al. 2007, Alexander et al. 2007, Yu, Lu & Lin 2007, Lu et al. astro-ph , Bartko et al. 2008, astro-ph , Hobbs & Nayakshin 2008 atsro-ph , Bonnell & Rice 2008 Science 321, 1060

11 Young massive stars near the BH massive cluster inspiral gas inflow & in situ formation in disk 1 light year Allen et al. 1990, Forrest et al. 1987, Krabbe et al. 1991, 1995, Gerhard 2001, Levin & Beloborodov 2003, Genzel et al. 2003, Kim et al. 2003, Portegies Zwart et al , Guerkan et al. 2005, Paumard et al. 2006, Martins et al. 2007, Alexander et al. 2007, Yu, Lu & Lin 2007, Lu et al. astro-ph , Bartko et al. 2008, astro-ph , Hobbs & Nayakshin 2008 atsro-ph , Bonnell & Rice 2008 Science 321, 1060

12 stellar surface density (stars arcsec -2-2 ) late y=23.4*(x/0.374) type stars K 15.5 ( -0.5) y=23.4*(x/0.374) B-stars K ( -0.75) s 16 B-stars all K 15.5 K s 17 Where is the stellar all stars cusp? K s 17 distance (parsec) S-stars Bahcall & Wolf cusp 1 (0.04 pc) R ~ 1 light month 10 1 young B old, late distance from SgrA* (arcseconds) Bahcall & Wolf 1976, Genzel et al.1996, 2003, Eisenhauer et al. 2005, Schödel et al. 2007, Bartko et al. 2009b, Buchholz et al. 2009, Do et al. 2009, Dale et al. 2009, Alexander 2005, Merritt 2006, 2009, Dale et al. 2009, Davies 2010

13 vlv [erg/s] cm vlv [erg/s] X-rays mm submm midinfrared near infrared Why is SgrA* so faint? 1E+37 1E+37 Synchrotron model 1E+36 1E+35 no blue blump 1E+36 1E+35 IC model 1E+34 1E+33 1E+32 Synchtron Nonthermal electrons Inverse Compton Bremsstrahlung 1E+34 1E+33 1E+32 x 10 x 1 x 0.01 Steady state model SSC model x 0.1 1E+31 1E+31 1E+08 1E+10 1E+12 1E+14 1E+16 1E+18 1E+20 1E+08 1E+10 1E+12 1E+14 1E+16 1E+18 1E+20 v [Hz] L SgrA* ~ erg/s ~ 10-8 L edd, η radiation ~10-6 v [Hz] VLA radio image Baganoff et al. 2001, Genzel et al Nature 425, Ghez et al. 2004, Eckart et al. 2006, Dodds-Eden et al. 2009

14 3.8 m flux density (mjy) X-ray count rate (s -1 ) Why is SgrA* so faint? 60 XMM 3.8 m 0.8 low L/L Edd is a combination of: 0.6 low accretion rate at Bondi radius low efficiency angular momentum transport most of the gas arriving at a few R s ejected back out time after UT 0:0:0 on Apr 4, 2007 (minutes) VLA radio image Baganoff et al. 2001, Genzel et al Nature 425, Ghez et al. 2004, Eckart et al. 2006, Dodds-Eden et al. 2009

15 Yet another surprise: a gas cloud falling straight into the hole Gillessen et al. Nature 481, 2012, stimulating: Burkert et al. 2012, Schartmann et al. 2012, Murray-Clay & Loeb 2012, Miralda-Escude 2012, Meyer & Meyer-Hofmeister 2012, Moscibrodzka et al. 2012

16 a b c d e

17 offset from SgrA* (arcsec) 2012 VLT Observations tidally disrupting head t int ~12 hr SINFONI+LGSF H+K co-add Brγ, HeI, Pα tail Gillessen et al. Orbit fit 2012 semi major axis (mas) 521 ± ± 39 Eccentricity ± ± inclination [ ] ± ± 0.81 position angle of ascending ± ± 1.1 node [ ] longitude of periastron [ ] ± ± 0.74 epoch of periastron [yr] ± ± 0.04 orbital period [yr] ± ± 18 R(peri)/R S radial velocity (km/s) Gillessen et al. 2012b astro-ph

18 A perfect example of spaghetti-fication Simulation of tidal disruption on a ballistic orbit Gillessen et al. 2012b astro-ph

19 the future: zooming in on the horizon 8m 39 m EELT 200m GRAVITY experiment (Eisenhauer et al. 2006, 2010) near-ir precision interferometric astrometry (10μarcsec~R s, K s <19) (sub)-millimeter Very Long Baseline Interferometry ( Event Horizon Telescope ) (Doeleman et al. 2011) ESO-VLTI