The Galactic Center
some recent highlights
Reinhard Genzel
MPE & UCB Physics
see Genzel, Eisenhauer & Gillessen arXiv:1006.0064
(Rev.Mod.Phys.)
a complete orbit: S2
2010
1992
M= 4.30(±0.20)stat(0.30)sys x106 M
R0= 8.28 (±0.15)stat(±0.29)sys kpc
SgrA*
2001
2002
Ghez et al. 2008, Gillessen et al. 2009a,b
Ghez et al. 2008, Gillessen et al. 2009 a,b
Avery
Broderick’s
dream of the
future
SgrA*
104
103
R/Rs
102
10
Reid & Brunthaler 2004
1
θFWHM (1.3mm) =
37 (+5,-3) μarcsec < θmin(lensing)
vpm 2 (2σ), 20 km/s
expected Brownian motion: 0.2 km/s
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. 2004-06, Bartko et al. 2007, Doeleman et al. 2008, Falcke,
Melia & Algol 2000, Broderick & Loeb 2006, 2007, Fish et al. 2009
could SgrA* be a binary ?
allowed
excluded
Milosavljevic & Hansen 2003, Mikkola & Merritt 2008, Gualandris & Merritt 2007, 2009, Gillessen et al. 2009a
mass distribution of the nuclear
cluster
R/Rs
3
4
10
5
10
10
S-stars
S2
7
10
10
old
stars
clockwise
disk
7
enclosed mass (solar masses)
6
10
dynamical detection of
stellar mass at 1pc and light
allows a range
of IMF and central
concentrations
CND
6
10
=1.8
2 limit
non-closure
S2-orbit
5
10
=0
SBH
4
10
=1.75
10
2
WD
SBH
3
10
the exact numbers are
important for LISA inspiral
event rates and
perturbation of S-star orbits
MS
NS
=1.3
0.001
Ro= 8.3 kpc
MS
0.01
0.1
1
10
radius (parsec)
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. 2010
The paradox of youth:
young stars
near the BH
IRS16 SW (Ofpe/LBV)
1
0
2.04 2.06 2.08 2.10 2.12 2.14 2.16 2.18 2.20
wavelength (m)
~180 OB stars in the central parsec !
IRS16SE2 (WN5/6)
0.1
0
-0.1
2.05
and exhibit
ordered motion
2.10
2.15
2.20
2.25
2.30
2.35
2.40
wavelength (m)
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
1.0
0.9
1 light year
2.10
2.15
2.20
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. 2003. 2004, 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 ?
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. 2003. 2004, 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
Top heavy IMF
dN / dm  m 2.3
limits on A-stars in ‘deep’ fields
dN / dm  m0.45  0.3
<m ~ 30 M
PMF (KLF)= IMF
for young population
and at high mass end of continuous
star formation
only believable case for significantly top heavy IMF ? (Bastian 2010)
Paumard et al. 2006, Bartko et al. 2010, Buchholz et al. 2009, Nayakshin & Sunyaev 2005
Star formation history in
central parsec
over ≥1pc and 10 Gyrs: IMF cannot have been as flat as in disk(s)
Pfuhl 2010: =0.85
Pfuhl 2010 red clump: =2.35 (ml=2.35), R2.5pc
Blum 2003 bright giants: =2.35 (ml=0.7), R2.5pc
red supergiants: =-0.85, R2.5pc
red supergiants: =-0.85, R1pc
6 Myr star disk(s): =-0.85, R1 pc
-1
10
10
10
formed stars (Msun)
-1
star formation rate (Msun yr )
10
-2
-3
10
7
10
6
10
5
10
4
10
3
-4
10
6
10
7
10
8
10
9
look-back time t (yr)
10
10
10
6
10
7
10
8
10
9
10
10
look-back time t (yr)
Blum et al. 2003, Maness et al. 2007, Pfuhl et al. 2010, Löckmann et al. 2010
late type stars K15.5
B-stars Ks16
B-stars K15.5
O/WR-stars clockwise
Ks<12.5 AGB stars
amplitude of red clump in KLF
all stars Ks17
is there a stellar
cusp ?
distance (parsec)
0.01
1
1”
(0.04 pc)
red clump
depth
1
amplitude of red clump in KLF
10
1
S-stars
-2
stellar surface density (stars arcsec )
100
0.1
R ~ 1 light month
0.1
B
late
O/WR
0.01
0.001
0.1
 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
0.0001
AGB
 collisions? initial conditions ? top
heavy IMF ? gouging by IMBH?
0.01
1
10
distance from SgrA* (arcseconds)
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
properties of cusp star orbits
monitoring the orbits of the innermost 100 stars in the
central light year; currently 35 orbits
near-isotropic, random
orientation (p=74%)
eccentricties ~2σ greater
than thermal distribution
Gillessen et al. 2009a
thermal
evidence for remnants
evidence for stellar remnant binaries from X-ray (radio) transients
Muno et al. 2005
how did the young stars get into the central pc ?
star disk(s)
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
central cusp
+
-
-
-
-
+?
Alexander, Merritt, Gerhard, Hills, Nayakshin, Levin, Bonnell, Tremaine, Morris, Portegies Zwart, Perets
hyper velocity stars
expected ejection rate 10-5 yr-1:
~103 HVs within 100 kpc
Brown et al. 2005, 2006, 2008, 2010, Hills 1989, Yu & Tremaine 2003
Emission from SgrA*
cumulative flux distribution
X-rays
IC model
1E+35
Synchtron
Nonthermal
electrons Inverse
Compton
1E+33
Synchrotron model
1E+36
vLv [erg/s]
cm
1E+34
probability of Flux(mJy)
vLv [erg/s]
1E+35
1E+37
L’-band VLT
near infrared
Do et al. 2009
6 epochs 2005-2007
red power law PSD
mm
1E+36
submm
1E+37
midinfrared
Dodds-Eden et al. 2010:
40 epochs 2004-2009
1E+32
1E+34
SSC model
x 10
1E+33
Bremsstrahlung
1E+31
x1
x 0.1
XMM
x 0.01
Steady state model
1E+32
1E+31
1E+08
1E+10
1E+12
1E+14
1E+16
1E+18
1E+20 1E+08
v [Hz]
0
4
8
12
16
dereddened Flux (mJy)
1E+10
1E+12
1E+14
1E+16
1E+18
1E+20
v [Hz]
20
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. 2010
magnetic reconnection
magnetic reconnection event
acceleration of electrons, drop in B-field
IR/X-synchrotron radiation
adiabatic expansion
Dodds-Eden et al. 2010a
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. 2006-2010, Markoff 2010, Melia & Falcke 2001
The potential of GC
measurements for new
constraints on GR
6 RS
RS ~ 10 µas
Earth Orbit
central
cusp
BH merger gravitational
wave pattern
S-star orbits
Psaltis 2004
field curvature
flares
+submm
strong field effects:
photon orbit….
radial & L-T precess.
Q2=J2/M (no hair)
post-Newt. to β2
(grav.redshift,
transv. Doppler)
Eisenhauer et al. 2008,
Rubilar & Eckart 2001, Weinberg
et al. 2005, Zucker et al. 2006,
Will 2008, Merritt et al. 2010