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
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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
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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
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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)
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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 !
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Sgr A*’s Apparent Sgr A*’s Apparent MotionMotion
• Moves mostly along
Galactic Plane
• Slight deviation from VSUN
Gal Plane
Best Fit
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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…
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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
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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
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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…
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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 …
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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
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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
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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
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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
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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
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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
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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