An Improved Distance and Mass Estimate for Sgr A* from a Multistar Orbit Analysis

Abstract

We present new, more precise measurements of the mass and distance of our Galaxy's central supermassive black hole, Sgr A*. These results stem from a new analysis that more than doubles the time baseline for astrometry of faint stars orbiting Sgr A*, combining two decades of speckle imaging and adaptive optics data. Specifically, we improve our analysis of the speckle images by using information about a star's orbit from the deep adaptive optics data (2005 - 2013) to inform the search for the star in the speckle years (1995 - 2005). When this new analysis technique is combined with the first complete re-reduction of Keck Galactic Center speckle images using speckle holography, we are able to track the short-period star S0-38 (K-band magnitude = 17, orbital period = 19 years) through the speckle years. We use the kinematic measurements from speckle holography and adaptive optics to estimate the orbits of S0-38 and S0-2 and thereby improve our constraints of the mass ($M_{bh}$) and distance ($R_o$) of Sgr A*: $M_{bh}=4.02\pm 0.16\pm 0.04\times 10^6{M}_{\odot }$ and $7.86\pm 0.14\pm 0.04$ kpc. The uncertainties in $M_{bh}$ and $R_o$ as determined by the combined orbital fit of S0-2 and S0-38 are improved by a factor of 2 and 2.5, respectively, compared to an orbital fit of S0-2 alone and a factor of $\sim$2.5 compared to previous results from stellar orbits. This analysis also limits the extended dark mass within 0.01 pc to less than $0.13\times 10^6{M}_{\odot }$ at 99.7% confidence, a factor of 3 lower compared to prior work.

56 pages, 14 figures, accepted to ApJ

References in corpus (3)

• Stellar remnants in galactic nuclei: mass segregation
• The old nuclear star cluster in the Milky Way: dynamics, mass, statistical parallax, and black hole mass
• Photometric Stellar Variability in the Galactic Center

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