Monitoring Stellar Orbits Around the Massive Black Hole in the Galactic Center

Abstract

We present the results of 16 years of monitoring stellar orbits around the massive black hole in center of the Milky Way using high resolution near-infrared techniques. This work refines our previous analysis mainly by greatly improving the definition of the coordinate system, which reaches a longterm astrometric accuracy of ≈ 300 µas, and by investigating in detail the individual systematic error contributions. The combination of a long time baseline and the excellent astrometric accuracy of adaptive optics data allow us to determine orbits of 28 stars, including the star S2, which has completed a full revolution since our monitoring began. Our main results are: all stellar orbits are fit extremely well by a single point mass potential to within the astrometric uncertainties, which are now ≈ 6× better than in previous studies. The central object mass is (4.31 ± 0.06| stat ± 0.36| R0 ) × 10 6 M ⊙ where the fractional statistical error of 1.5% is nearly independent from R 0 and the main uncertainty is due to the uncertainty in R 0 . Our current best estimate for the distance to the Galactic Center is R 0 = 8.33 ± 0.35 kpc. The dominant errors in this value is systematic. The mass scales with distance as (3.95 ± 0.06) × 10 6 (R 0 /8 kpc) 2.19 M ⊙ . The orientations of orbital angular momenta for stars in the central arcsecond are random. We identify six of the stars with orbital solutions as late type stars, and six early-type stars as members of the clockwise rotating disk system, as was previously proposed. We constrain the extended dark mass enclosed between the pericenter and apocenter of S2 at less than 0.066, at the 99% confidence level, of the mass of Sgr A*. This is two orders of magnitudes larger than what one would expect from other theoretical and observational estimates.

Maser astrometry with VERA and Galactic structure

“…Although the number of sources is still around ∼ 40, as seen in table 1, Galactic parameters are constrained reasonably well. For instance, R 0 is determined at 5% level, and is consistent with recent determinations of R 0 which are independent of our results (e.g., Ghez et al 2008;Gillessen et al 2009). Ω 0 is also determined at 3% level, which can be converted into Θ 0 = 254 ± 14 km s −1 by adopting R 0 = 8.4 ± 0.4 kpc.…”

Sgr A*, the best-sampled of all AGN?

“…And [Gillessen et al, 2009] reported that S2 flared during its periastron passage in April 2002, by half a magnitude, and that six successive measurement points were offset towards Sgr A* through up to 10 marcsec in angle, reminiscent of a fata morgana at IR frequencies, see fig.7. These latter two facts are consistent with a (high) local plasma density n of some 10 12 cm −3 , as expected around a BD.…”

Diffuse gamma ray constraints on annihilating or decaying Dark Matter after Fermi

“…where the coordinate r, centered on the Galactic Center, reads r(s, ψ) = (r 2 + s 2 − 2 r s cos ψ) 1/2 , r = 8.33 kpc [11] is the most likely distance from the Sun to the Galactic Center (GC) and ψ is the angle between the direction of observation in the sky and the GC. In terms of the galactic latitude b and longitude l, one has cos ψ = cos b cos l .…”