The Galactic Center some recent highlights Reinhard Genzel MPE & UCB Physics see Genzel, Eisenhauer & Gillessen arXiv: arXiv: (Rev.Mod.Phys.)

a complete orbit: S Ghez et al. 2008, Gillessen et al. 2009a,b SgrA* M = 4.30(±0.20) stat (  0.30) sys x10 6 M  R 0 = 8.28 (±0.15) stat (±0.29) sys kpc

Ghez et al. 2008, Gillessen et al a,b

SgrA* Backer & Sramek 1996, Menten et al. 1997, Bower et al. 2003, 2005, Reid & Brunthaler 2004, Shen et al. 2005, Baganoff et al. 2001, 2003, Aharonian et al , Bartko et al. 2007, Doeleman et al. 2008, Falcke, Melia & Algol 2000, Broderick & Loeb 2006, 2007, Fish et al R/R s v pm  2 (2σ), 20 km/s expected Brownian motion: 0.2 km/s Reid & Brunthaler 2004 θ FWHM (1.3mm) = 37 (+5,-3) μarcsec < θ min (lensing) Avery Broderick’s dream of the future

Milosavljevic & Hansen 2003, Mikkola & Merritt 2008, Gualandris & Merritt 2007, 2009, Gillessen et al. 2009a could SgrA* be a binary ? excluded allowed

mass distribution of the nuclear cluster Genzel et al. 1996, Haller et al. 1996, Trippe et al. 2008, Schödel et al. 2009, Freitag et al. 2006, Hopman & Alexander 2007, Beloborodov et al. 2006, Gillessen et al. 2009a,b, Ghez et al. 2008, Bartko et al dynamical detection of stellar mass at 1pc and light allows a range of IMF and central concentrations the exact numbers are important for LISA inspiral event rates and perturbation of S-star orbits

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. 2008, Bartko et al. 1009a, Hobbs & Nayakshin 2008, Bonnell & Rice 2008, Kocsis & Tremaine light year The paradox of youth: young stars near the BH ~180 OB stars in the central parsec ! they can account for the entire FIR, UV and EUV luminosity of the Galactic Center and the excitation/ionization of the SgrA West HII region and exhibit ordered motion

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. 2008, Bartko et al. 1009a, Hobbs & Nayakshin 2008, Bonnell & Rice 2008, Kocsis & Tremaine 2010 The paradox of youth: young stars near the BH two warped & thick disks or a single, more complex structure ?

structure of star disk(s) Beloborodov et al. 2006, Paumard et al. 2006, Lu et al. 2009, Bartko et al. 2009, 2010, Gillessen et al. 2009a, Kocsis & Tremaine 2010 h z /R~ warp two warped disks or a single, more complex structure ? ~0.34

can a single initially cold accretion disk broaden to its current state by local interactions ? otherwise: two coeval disks: how did they form in the same region and at large angles, intercepting each other ? Nayakshin & Cuadra 2006, Levin et al. 2006, R. Alexander et al. 2007, Cuadra et al. 2008, Loeckmann et al. 2008, Perets et al. 2009, Kocsis & Tremaine 2010 no (Cuadra et al. 2008): scattering by other objects in nuclear cluster is by far not sufficient to broaden initially thin disk to >>10 0 in ~ 6 Myrs, even with a large number of IMBHs yes (Kocsis & Tremaine 2010): when the ‘graininess’ of the background star cluster is taken into account, warping and thickening of an initially thin disk is the inevitable result of resonant relaxation

Top heavy IMF Paumard et al. 2006, Bartko et al. 2010, Buchholz et al. 2009, Nayakshin & Sunyaev 2005 PMF (KLF)= IMF for young population and at high mass end of continuous star formation limits on A-stars in ‘deep’ fields only believable case for significantly top heavy IMF ? (Bastian 2010)

Paczynski 1978, Kolykhalov & Sunyaev 1980, Lin & Pringle 1987, Shlosman & Begelman 1989, Sanders 1998, Collin & Zahn 1999, Goodman 2003, Larson 2006, Nayakshin 2007, Alexander et al. 2008, Bonnell & Rice 2008, Hobbs & Nayakshin 2009, Ulubay-Siddiki et al top heavy IMF as a result of: accretion & merging in Keplerian disk, growth toward Hills/isolation mass >100 M  shock-heating brings Jeans mass to >>10 M  in-situ star formation from infalling gas currently: Q disks ~30-100

Star formation history in central parsec Blum et al. 2003, Maness et al. 2007, Pfuhl et al. 2010, Löckmann et al over ≥1pc and 10 Gyrs: IMF cannot have been as flat as in disk(s)

Bahcall-Wolf: ρ~r -7/4 cusp isothermal core is there a stellar cusp ? ρ * ~R -1.3±02 ~ R -1.5 –(m/(4M)) Genzel et al. 2003,Schödel et al. 2007, Alexander 2005, Merritt 2006 GC is one of the few nuclei where an equilibrium cusp may exist: since t relax ~t Hubble simulations by Freitag et al. (2006): in central 0.1pc (2.5”) 2400 stellar black holes 6500 main-seq. stars + giants 3000 WDs 400 neutron stars

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, Merritt 2009, Dale et al. 2009, Davies 2010 is there a stellar cusp ?  the cusp consists mainly of relatively massive young stars; their lifetime is too short to be relaxed by two-body relaxation  the old stars do not exhibit a cusp  collisions? initial conditions ? top heavy IMF ? gouging by IMBH? S-stars B O/WR AGB late red clump depth 1” (0.04 pc) R ~ 1 light month

near-isotropic, random orientation (p=74%) properties of cusp star orbits Gillessen et al. 2009a monitoring the orbits of the innermost 100 stars in the central light year; currently 35 orbits thermal eccentricties ~2σ greater than thermal distribution

evidence for remnants Muno et al evidence for stellar remnant binaries from X-ray (radio) transients

fainter stars very close to SgrA* automatic PSF subtraction of point sources Sabha et al ” NACO, , Ks SgrA* 92 mas/yr (3600 km/s) ‘astrometric confusion’

The Hills capture process Hills 1988, Gould & Quillen 2003, Yu & Tremaine 2003, Gualandris et al. 2005, Alexander 2007 ejection of high velocity star

Massive perturbers Spitzer & Schwarzschild 1951, Perets, Alexander & Hopman light years

resonant relaxation in a Keplerian potential S2 Rauch & Tremaine 1996, Hopman & Alexander 2007, Perets et al. 2009

how did the young stars get into the central pc ? star disk(s)central cusp in situ star formation: tidally disrupted ‘dispersion ring’ of gas + gravitational instability in disk + - external formation: transport by in-spiraling massive cluster (+ IMBH?) - - transport by scattering & relaxation: massive perturbers + Hills capture + resonant relaxation near BH - +? Alexander, Merritt, Gerhard, Hills, Nayakshin, Levin, Bonnell, Tremaine, Morris, Portegies Zwart, Perets

hyper velocity stars Brown et al. 2005, 2006, 2008, 2010, Hills 1989, Yu & Tremaine 2003 expected ejection rate yr -1 : ~10 3 HVs within 100 kpc

Emission from SgrA* Baganoff et al. 2001, Genzel et al. 2003,, Ghez et al. 2004, 2005, Eisenhauer et al. 2005, Gillessen et al. 2006, Eckart et al. 2005, 2006a/b, 2008, Trippe et al. 2007, Meyer et al. 2007, Porquet et al. 2008, Marrone et al. 2008, Do et al. 2008, Yusef-Zadeh et al. 2008, 2010, Dodds-Eden et al. 2009, 2010, Sabha et al L’-band VLT XMM Dodds-Eden et al. 2010: 40 epochs Do et al epochs red power law PSD probability of Flux(mJy) dereddened Flux (mJy) cumulative flux distribution

magnetic reconnection Baganoff et al. 2001, Genzel et al. 2003,, Ghez et al. 2004, 2005, Eisenhauer et al. 2005, Gillessen et al. 2006, Eckart et al. 2005, 2006a/b, 2008, Trippe et al. 2007, Meyer et al. 2007, Porquet et al. 2008, Marrone et al. 2008, Sharma et al. 2007, Do et al. 2008, Dodds-Eden et al. 2010a,b,Yusef-Zadeh et al , Markoff 2010, Melia & Falcke 2001 magnetic reconnection event acceleration of electrons, drop in B-field IR/X-synchrotron radiation adiabatic expansion Dodds-Eden et al. 2010a

The potential of GC measurements for new constraints on GR S-star orbits central cusp flares +submm BH merger gravitational wave pattern 6 R S Earth Orbit R S ~ 10 µas field curvature Psaltis 2004 post-Newt. to β 2 (grav.redshift, transv. Doppler) radial & L-T precess. Q 2 =J 2 /M (no hair) strong field effects: photon orbit…. Eisenhauer et al. 2008, Rubilar & Eckart 2001, Weinberg et al. 2005, Zucker et al. 2006, Will 2008, Merritt et al. 2010