2004 Mar 252004 Mar 25 Sgr A* at 30Sgr A* at 30

Must Sgr A* be a Super-Massive Black Hole?

Mark J. Reid Harvard-Smithsonian CfA

Andreas Brunthaler MPIfR/JIVE

2004 Mar 252004 Mar 25 Sgr A* at 30Sgr A* at 30

Discovery of Galactic Discovery of Galactic CenterCenter

Shapley (1918): Shapley (1918):

Globular Clusters “point” Globular Clusters “point” toto

Galactic CenterGalactic Center

RRoo = 13 kpc = 13 kpc

2004 Mar 252004 Mar 25 Sgr A* at 30Sgr A* at 30

Stellar OrbitsStellar Orbits

• 6 stars with orbits

• Enclosed mass: 4 x 106 Msun

< 100 AU radius Schoedel etal 02,03 Ghez et al 03

• Sgr A* within 100 AU Reid et al 03

2004 Mar 252004 Mar 25 Sgr A* at 30Sgr A* at 30

Sgr A*’s apparent Sgr A*’s apparent motionmotion

• Relative to 2 Quasars

• Sun’s Galactic Orbit:

220 km/s at 8.0 kpc =

6 mas/yr in Gal plane

(Kassim, Frail & Briggs)

2004 Mar 252004 Mar 25 Sgr A* at 30Sgr A* at 30

Project HistoryProject History

1979: Proposal to US VLBI Network1979: Proposal to US VLBI Network– ““To Study Feasibility of Detecting To Study Feasibility of Detecting

Proper Motion of the Galactic Center”Proper Motion of the Galactic Center”– 15 GHz; OVRO, HRAS, GB, Haystack15 GHz; OVRO, HRAS, GB, Haystack– Failed:Failed:

Scatter broadened Sgr A*Scatter broadened Sgr A* Limited sensitivityLimited sensitivity

Needed VLBA !Needed VLBA !

2004 Mar 252004 Mar 25 Sgr A* at 30Sgr A* at 30

Sgr A*’s Apparent Sgr A*’s Apparent MotionMotion

• Moves mostly along

Galactic Plane

• Slight deviation from VSUN

Gal Plane

Best Fit

2004 Mar 252004 Mar 25 Sgr A* at 30Sgr A* at 30

Sgr A* motion Galactic Sgr A* motion Galactic Coords:Coords:

• Motion in Galactic Plane:

o/Ro = 29.4 +/- 0.9 km/s/kpc

Compare to

(A-B)/Ro= 27.2 +/- 0.9 km/s/kpc

(Feast & Whitelock 1997)

• Motion out of Galactic Plane:

Very small…

2004 Mar 252004 Mar 25 Sgr A* at 30Sgr A* at 30

Sgr A* motion toward Galactic Sgr A* motion toward Galactic PolePole

• Solar Motion 7 km/s

• Sgr A*s peculiar motion

-0.4 +/- 0.8 km/s

2004 Mar 252004 Mar 25 Sgr A* at 30Sgr A* at 30

If Sgr A* is not a If Sgr A* is not a SMBH…SMBH…

• 1) Tight binary black hole

Decays by Grav Radiation

• 2) Theoretically “flexible”

eg, density power law: r

2004 Mar 252004 Mar 25 Sgr A* at 30Sgr A* at 30

If Sgr A* is not a If Sgr A* is not a SMBH…SMBH…

• V >> 1 km/s for any dark matter distribution, unless Mdark ~ 0

• Would be easily observed, except…

2004 Mar 252004 Mar 25 Sgr A* at 30Sgr A* at 30

Sgr A* “orbital period”Sgr A* “orbital period”

• Measured V (& A) not sensitive to P<16 yrs

• Essentially all dark mass distributions give P<16 yrs

• But still detectable …

2004 Mar 252004 Mar 25 Sgr A* at 30Sgr A* at 30

Sgr A* orbital Sgr A* orbital excursionsexcursions

• Would easily see excursions > 4 AU

• Sgr A* either

i) ~4 x 106 Msun

ii) “bound” within

4 AU4 AU

2 AU

2004 Mar 252004 Mar 25 Sgr A* at 30Sgr A* at 30

Effect of Bound Stars on Effect of Bound Stars on Sgr A*Sgr A*

Recipe:

1. Put 4 x 106 stars in computer

2. Place SMBH/dark mass at center of mass of system

3. Solve Kepler’s Eq for each star

4. Calculate COM after 8 years

5. Determine position & then velocity of SMBH

6. Repeat as needed to get Vrms

• Standard IMF

• eccentricities from 0 to 0.99

2004 Mar 252004 Mar 25 Sgr A* at 30Sgr A* at 30

Sgra A* must be Sgra A* must be massive…massive…

• Compare simulated systems with trial measurements

• Sgr A*’s mass (Msun) Maximum liklihood lower limit: 1.2 x 106 90% confidence lower limit: 0.2 x 106

• Very conservative calculation; ignored effects of… Possible dark cluster of stellar remnants, Stellar clumping/collective effects, Stars beyond 2 pc

2004 Mar 252004 Mar 25 Sgr A* at 30Sgr A* at 30

Effects of Stellar Effects of Stellar RemnantsRemnants

• 10% of mass <100 AU in stellar remnants

• Plummer distribution of Mouawad et al 2004

• Vz(SgrA*) > 0.3 km/s for 0.01 < a < 2 pc

2004 Mar 252004 Mar 25 Sgr A* at 30Sgr A* at 30

Exotic Dark Matter Exotic Dark Matter ??

Could exotic dark matter dominate the G.C. Could exotic dark matter dominate the G.C. mass?mass?

Not likely … less than 30% of mass & Not likely … less than 30% of mass & dropping dropping

Tied radiative source to the mass…Tied radiative source to the mass…

“ “Fermion ball” can’t give Sgr A*’s SEDFermion ball” can’t give Sgr A*’s SED

First time ~10First time ~1066 M Msunsun tied tied directlydirectly to an AGN to an AGN

2004 Mar 252004 Mar 25 Sgr A* at 30Sgr A* at 30

Must Sgr A* be a Must Sgr A* be a SMBH?SMBH?Object Density Method Mass & RadiusObject Density Method Mass & Radius (M(Msunsun/pc/pc33))

M 87 2 x 10M 87 2 x 106 6 HST: 3x10HST: 3x1099 M Msunsun in 7 pc in 7 pcNGC 4258 7 x 10NGC 4258 7 x 109 9 VLBAVLBA : : HH22OO 3x103x1077 M Msunsun in 0.1 pc in 0.1 pc

Sgr A* 8 x 10Sgr A* 8 x 1015 15 S2’s orbit 4x10S2’s orbit 4x1066 M Msunsun in 0.001 pc in 0.001 pcSgr A* 2 x 10Sgr A* 2 x 1022 22 Sgr A*s p.m. 1x10Sgr A*s p.m. 1x1066 M Msunsun in 0.5 AU in 0.5 AU

SMBH 2 x 10SMBH 2 x 1025 25 RRschsch 4x104x1066 M Msunsun in 0.08 AU in 0.08 AU

VLBI (eg, SMA-ALMA-LMT-CARMA…) @ 1 mm -> 20 uasVLBI (eg, SMA-ALMA-LMT-CARMA…) @ 1 mm -> 20 uas10 uas @ 8 kpc

2004 Mar 252004 Mar 25 Sgr A* at 30Sgr A* at 30

The Utimate The Utimate Proof/PrizeProof/Prize

• Image SMBH with resolution ~RSch

• Show all of the mass is contained within ~3RSch

• See how accretion disk, black hole, and jets work