Measuring distance and properties of the Milky Way's central supermassive black hole with stellar orbits

Creators: Ghez, A. M.; Salim, S.; Weinberg, N. N.; Lu, J. R.; Do, T.; Dunn, J. K.; Matthews, K.; Morris, M. R.; Yelda, S.; Becklin, E. E.; Kremenek, T.; Milosavljevic, M.; Naiman, J.

Abstract

We report new precision measurements of the properties of our Galaxy's supermassive black hole. Based on astrometric (1995-2007) and radial velocity (RV; 2000-2007) measurements from the W. M. Keck 10m telescopes, a fully unconstrained Keplerian orbit for the short-period star S0-2 provides values for the distance (R_0) of 8.0±0.6 kpc, the enclosed mass (M_(bh)) of 4.1±0.6x10^6 M☉ and the black hole's RV, which is consistent with zero with 30 km/s uncertainty. If the black hole is assumed to be at rest with respect to the Galaxy (e. g., has no massive companion to induce motion), we can further constrain the fit, obtaining R_0 = 8.4±0.4kpc and M_(bh) 4.5±0.4x10^6 M☉. More complex models constrain the extended dark mass distribution to be less than 3-4x10^5 M☉ within 0.01 pc, ~100 times higher than predictions from stellar and stellar remnant models. For all models, we identify transient astrometric shifts from source confusion (up to 5 times the astrometric error) and the assumptions regarding the black hole's radial motion as previously unrecognized limitations on orbital accuracy and the usefulness of fainter stars. Future astrometric and RV observations will remedy these effects. Our estimates of R_0 and the Galaxy's local rotation speed, which it is derived from combining R_0 with the apparent proper motion of Sgr A*, (θ_0 = 229±18 km/s), are compatible with measurements made using other methods. The increased black hole mass found in this study, compared to that determined using projected mass estimators, implies a longer period for the innermost stable orbit, longer resonant relaxation timescales for stars in the vicinity of the black hole and a better agreement with the M_(bh)-σ relation.

Additional Information

© 2008. The American Astronomical Society. Print publication: Issue 2 (2008 December 20) Received 2008 June 17, accepted for publication 2008 August 2008 We thank the staff of the Keck Observatory, especially Joel Aycock, Randy Campbell, Al Conrad, Jim Lyke, David LeMignant, Chuck Sorensen, Marcos Van Dam, Peter Wizinowich, and director Taft Armandroff for all their help in obtaining the new observations. We also thank Brad Hanson, Leo Meyer, and Clovis Hopmann for their constructive comments on the manuscript, and the referee, Rainer Schodel, for his helpful suggestions. Support for this work was provided by NSF grant AST 04-06816 and the NSF Science and Technology Center for Adaptive Optics, managed by the University of California, Santa Cruz (AST 98-76783), and the Levine-Leichtman Family Foundation. The W. M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

Attached Files

Published - GHEapj08.pdf

Files

GHEapj08.pdf

Files (882.0 kB)

Name	Size	Download all
GHEapj08.pdf md5:d06a85025234584e4df53423e4b9f15a	882.0 kB	Preview Download

Additional details

	All versions	This version
Views	0	0
Downloads	0	0
Data volume	0 Bytes	0 Bytes