D.Seal/JPL D.Seal/JPL The Hipparcos Catalogue (118000 stars) The second Tycho Catalogue (2.5million stars) 5–1 D.Seal/JPL The Galactic Center The Yale Bright Star Catalogue (9110 brightest stars)

ALEX O AN IC D R R

E I D A N I

E

R

F

S

I

G E

I A

I L

L

M

V

E

M

D A C A 7 6 5–7 5–8 (1564–1642; Sidereus (1738–1822): First Milky way is not “milky”! ⇒ = heliocentric! Galileo Galilei Nuncius): Telescopes resolves (part of) the milky way in stars, discoversstars new attempts to determine morphology of the Galaxy. Note: William Herschel The Night Sky, VI The Night Sky, VII

ALEX ALEX O AN O AN IC D IC D R R R R

E I E I

N D A N D A I I

E E

R R

F F

S S

I I

G G E E

I I A A

I I L L

L L

M M

V V

E E

M M

D D A A C C A A The Milky Way The Milky Way ◦ 40 × ◦ Milky way in Sagittarius 27 M9 NGC 6334 NGC 6357 Scorpius M6 Ophiuchus M23 M7 M22, KPNO (N.A.Sharp, REU program/NOAO/AURA/NSF) M20 M8 M21 M16 M24 M28 M17 M69 M25 M22 Sagittarius M54 Scutum NGC 6723 W. Keel (U Alabama) 8 5–9 π km sin b 13 π ◦ 10 40 × × 3 ◦ = Milky way in Sagittarius 27 stellar parallax (1784–1846): First 26Lj r . 3 π = d reminder: 1 parsec Wilhelm Bessel determination of a The Night Sky, VIII W. Keel (U Alabama)

ALEX O AN IC D R R

E I D A N I

E

R

F

S

I

G E

I A

I L

L

M

V

E

M

D A C A The Milky Way F E RIDE IA R M IC E O D

A A

C L

A E

X

A M

N

V

D L

R L

I

I

G I A S E N 5–19 10 Milky way as a Galaxy

30 12 20 RR Lyrae 14 10 V 0 Z [kpc] Luminosity 16 −10 Luminosity: ∼ 2 × 1010 18 −20 Galactic L⊙ X Center 11 Mass: ∼10 M⊙ (radiating) −30 12 0 0.5 1 8 kpc −20 −10 0 10 20 30 40 12 kpc ∼10 M⊙ (total) (b−y) X [kpc] Temperature Stellar density: −3 Sun ∼ 0.3 M⊙ pc

208 km/s 220 Mill years/revolution 33 30 Galactic center has a distance of 8kpc 1 M⊙ = 2 × 10 g = 2 × 10 kg, 33 −1 26 1 L⊙ = 4 × 10 ergs = 4 × 10 W

M83: ESO [VLT ANTU+FORS1]

Richteretal.,1999,A&A350,476 M22,KPNO(N.A.Sharp,REUprogram/NOAO/AURA/NSF) The Milky Way 18

F E RIDE IA R M IC E O D

A A

C L

A E

X

A M

N

V

D L

R L

I

I

G I A S Ophiuchus E N 5–19 Scutum Milky way as a Galaxy M16

M17 M9

M23 600 pc

M24 2kpc M25 X M21 M20 M22 M28 8 kpc 12 kpc M8 10 Galactic Luminosity: ∼ 2 × 10 L⊙ X Center 11 Sagittarius Milky way in Saggitarius Mass: ∼10 M⊙ (radiating) M54 12 M69 M6 27◦ × 40◦ ∼10 M⊙ (total) M7 NGC 6357 Galactic Stellar density: X Center Distance: 8kpc −3 12 kpc 8 kpc ∼ 0.3 M⊙ pc NGC 6723 =⇒ 1◦ ∼ 140pc NGC 6334 ′ =⇒ 1 ∼ 2pc Sun 208 km/s 33 30 ′′ 220 Mill years/revolution 1 M⊙ = 2 × 10 g = 2 × 10 kg, =⇒ 1 ∼ 0.3pc 33 −1 26 Scorpius 1 L⊙ = 4 × 10 ergs = 4 × 10 W 1 kpc NGC 4565: W. McLaughlin

W. Keel (U Alabama) The Milky Way 19 2MASS: inner 60◦ × 45◦ Problem: strong extinction due to dust 12 (AV ∼ 30mag: 10 times reduction in the optical!) =⇒ Multiwavelength astronomy!

2MASS/MSX: Inner 4◦ × 2◦ Infra red: Dust becomes transparent! 2MASS (J [1.25 µm], red), (K [2.17 µm], green), MSX (A [6–11 µm], blue)

2MASS: 3 IR Bänder: J (1.25 µm), H (1.65 µm), Ks (2.17µm) Sgr A West (“spiral”): 2 pc diameter,

∼ 60 M⊙ ionized gas, shaped by tidal forces (probably influence of mG B-field), northern arm falls on center, east and south arms rotate. around Sgr A West: circumnuclear disk of molecular gas, (r ∼ 2 pc). total mass accretion rate onto Sgr A∗: −1 ∼ 0.03 M⊙ yr Sgr A (3.6 cm, courtesy K.Y. Lo/NRAO/AUI)

X

F E RIDE IA R M IC E O D

A A

C L

A E

X

A M

N

V

D L

R L

I

I

G I A S E N 5–25 The Inner kpc

Radio source Sgr A: Sgr A (West) (Arc): 5′′ (=0.2pc) broad IRS 8 northern IRS 7 radio filaments, part of a much larger arm Sgr A West (“spiral”): Ω-shaped structure ⊥ galactic plane. 2 pc diameter, eastern ∼ 60 M ionized gas, shaped by arm ⊙ tidal forces polarized, steep radio spectrum =⇒ Sgr A* synchrotron radiation (nonthermal (probably influence of mG B-field), northern arm falls on center, east electrons; ∝ −p)! southern ne(E) E arm and south arms rotate. caused by shocks from supernovae? circumnuclear around Sgr A West: circumnuclear ring disk of molecular gas, (r ∼ 2 pc). total mass accretion rate onto 70pc × 70pc, VLA (F. Yusef-Zadeh et al., 1982–1984) Sgr A∗: c NRAO/AUI −1 ∼ 0.03 M⊙ yr Sgr A (3.6 cm, courtesy K.Y. Lo/NRAO/AUI)

The Path to the Galactic Center 6 F E RIDE IA R M IC E O D

A A

C L

A E

X

A M

N

V

D L

R L

I

I

G I A S E N 5–30 The Inner Parsec: Central Cluster, II

Sgr A West (“spiral”): Observations are difficult because 2 pc diameter, of astronomical seeing ∼ 60 M ionized gas, shaped by ⊙ (∼ 0.7′′=0.2 pc) tidal forces (probably influence of mG B-field), northern arm falls on center, east and south arms rotate. around Sgr A West: circumnuclear disk of molecular gas, (r ∼ 2 pc). total mass accretion rate onto Sgr A∗: −1 ∼ 0.03 M⊙ yr Sgr A (3.6 cm, courtesy K.Y. Lo/NRAO/AUI) Gemini North/AURA

The Galactic Center 5

F F E RIDE E RIDE IA R IA R M IC M IC E O E O D D

A A A A

C C L L

A A E E

X X

A A

M M

N N

V V

D D L L

R R L L

I I

I I

G G I I A A S S E E N 5–29 N 5–30 The Inner Parsec: Central Cluster, I The Inner Parsec: Central Cluster, III

Observations are difficult because of astronomical seeing (∼ 0.7′′=0.2 pc) Center of Sgr A contains massive ...which can be corrected by and dense cluster 6 −3 adaptive optics (> 10 M⊙ pc , compare solar −3 =⇒ resolution: diffraction limit! neighborhood: 0.1 M⊙ pc ) Spectroscopy: Stars are rich in θ = 1.22 rad · λ/d ∼ 1mas Helium, early type (=massive), strong winds (for d = 8 m, λ = 2.2 µm) −1 (vWind ∼ 1000kms ). =⇒ 140AU for gal. center! Gemini North/AURA

The Galactic Center 4 The Galactic Center 6 1996 2000 Genzel/Eckart Genzel/Eckart 7 5–31 1994 20" / 0.8 pc m) (Genzel/Eckart) The Inner Parsec: Central Cluster, IV µ N Genzel/Eckart 2.76’ / 6.6 pc

ALEX O AN IC D R R

E I D A N I

E

R

F

S

I

G E

I A

I

L E

L

M

V

E

M

D A C A VLT ISAAC K-Band (2.2 The Galactic Center F E RIDE IA R M IC E O D

A A

C L

A E

X

A M

N

V

D L

R L

I

I

G I A S E N 5–37 The inner parsec: mass determination

Model: point source plus cluster with a velocity dispersion of 50kms−1 =⇒ 6 central mass: 2.4 × 10 M⊙. Eckart & Genzel, 1997, MNRAS, 284, 576 Evidence for a very massive compact object in the Galactic center =⇒ Genzel et al. (MPE)/Ghez et al. (UCLA): dynamical mass determination by Black Hole? measuring the proper motion of ∼ 40 stars of the central cluster (Fig.: MPE results 1991–2000). The Galactic Center 13

F E RIDE IA R M IC E O D

A A

C L

A E

X

A M

N

V

D L

R L

I

I

G I A S E N 5–36 The inner parsec: mass determination

Velocity dispersion in the center For r ≥ 0.057pc: Keplerian −1/2 velocity profile (σv ∝ v ), influenced by cluster at smaller distances Eckart & Genzel, 1997, MNRAS, 284, 576

ESO, Oct 2002 The Galactic Center 12 18 5–40 Schödel et al. (2002) ⊙ M 6 10 × ) 0 . 1 The inner parsec: mass determination ± 7 . 3 =( BH

ALEX O AN IC D R R E I

The center of the Galaxy harborsM a black hole with D A N I

E

R

F

S

I

G E

I A

I L

L

M

V

E

M

D A C A Ghez et al. (2003) The Galactic Center 17 5–40 Schödel et al. (2002) ) BH M 2 π + 4 ∗ m ( G = 2 3 a P ⇒ = 2 years . 5light days . 15 5 = = The inner parsec: mass determination a P

ALEX O AN IC D R R

E I D A N I

E

R

F

S

I

G E

I A

I L

L

M

V

E

M

D A C A Mass determination: 3. Kepler Ghez et al. (2003) The Galactic Center