------------------------------------------------------------------------ reid_gcnews.tex ApJ, Dec 2004, in press Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-MailScanner-Information: Please contact postmaster@aoc.nrao.edu for more information X-MailScanner: Found to be clean X-MailScanner-SpamCheck: not spam, SpamAssassin (score=-5.4, required 7, BAYES_01 -5.40, USER_AGENT_PINE 0.00) % astro-ph/0408107 \documentclass[12pt,preprint]{aastex} \newcommand{\masyr} {mas y$^{-1}$} \newcommand{\sgra} {Sgr~A*} \newcommand{\sgrab} {Sgr~A*~} \newcommand{\tnot} {\ifmmode {\Theta_0}\else {$\Theta_0$} \fi} \newcommand{\rnot} {\ifmmode {R_0} \else {$R_0$} \fi} \newcommand{\onot} {\ifmmode {\Omega_0}\else {$\Omega_0$} \fi} \newcommand{\vsun} {\ifmmode {V_\odot} \else {$V_\odot$} \fi} \newcommand{\peryr} {y$^{-1}$} \newcommand{\persec} {s$^{-1}$} \newcommand{\perkpc} {kpc$^{-1}$} \newcommand{\porm} {\ifmmode {~\pm~} \else {$~\pm~$} \fi} \newcommand{\kms} {\ifmmode {{\rm km~s}^{-1}} \else {km~s$^{-1}$} \fi} \newcommand{\msun} {\ifmmode {{\rm M}_\odot} \else {${\rm M}_\odot$} \fi} \newcommand{\Msun} {\ifmmode {{\rm M}_\odot} \else {${\rm M}_\odot$} \fi} \newcommand{\lsun} {\ifmmode {{\rm L}_\odot} \else {${\rm L}_\odot$} \fi} \newcommand{\vmax} {\ifmmode {V_{\rm max}} \else {$V_{\rm max}$} \fi} \newcommand{\dNdr} {\ifmmode {dN \over dr} \else {$dN \over dr$} \fi} \newcommand{\ie} {i.e.,~} \newcommand{\eg} {eg,~} \newcommand{\etal} {et al.~} \newcommand{\fifty} {{1950}} \newcommand{\twoth} {{2000}} \newcommand{\Mr} {\ifmmode {M_r} \else {$M_r$} \fi} \newcommand{\Mtotal} {\ifmmode {M_{{\rm total}}} \else {$M_{{\rm total}}$} \fi} \newcommand{\rmin} {\ifmmode {r_{{\rm min}}} \else {$r_{{\rm min}}$} \fi} \newcommand{\rmax} {\ifmmode {r_{{\rm max}}} \else {$r_{{\rm max}}$} \fi} \newcommand{\rhonot} {\ifmmode {\rho_0} \else {$\rho_0$} \fi} \newcommand{\dm} {\ifmmode {\delta m} \else {$\delta m$} \fi} \newcommand{\twopi} {\ifmmode {2\pi} \else {$2\pi$} \fi} \newcommand{\pg} {{\phantom >}} \newcommand{\pl} {{\phantom <}} \shorttitle{The Mass of \sgra} \shortauthors{Reid \& Brunthaler} \begin{document} \title{The Proper Motion of \sgra: II. The Mass of \sgra} \author{M.~J.~Reid} \affil{Harvard--Smithsonian Center for Astrophysics, Cambridge, MA 02138} \email{mreid@cfa.harvard.edu} \author{A.~Brunthaler} \affil{Max-Planck-Institut f\"ur Radioastronomie, Auf dem H\"ugel 69, D-53121 Bonn, Germany and Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands} \email{brunthaler@jive.nl} \begin{abstract} We report measurements with the VLBA of the position of \sgrab with respect to two extragalactic radio sources over a period of eight years. The apparent proper motion of \sgrab relative to J1745--283 is $6.379\pm0.024$~mas~\peryr\ along a position angle of $209.60 \pm 0.18$ degrees, almost entirely in the plane of the Galaxy. The effects of the orbit of the Sun around the Galactic center can account for this motion, and the residual proper motion of \sgrab perpendicular to the plane of the Galaxy is $-0.4\pm0.9$~\kms. A maximum-likelihood analysis of the motion expected for a massive object within the observed Galactic center stellar cluster indicates that \sgrab contains more than about 10\% of the $\approx4 \times 10^6~\msun$ deduced from stellar orbits. The intrinsic size of \sgra, as measured by several investigators, is less than 1~AU, and the implied mass density of $\sim10^{22}$~\msun pc$^{-3}$ is within about three orders of magnitude of a comparable super-massive black hole within its Schwarzschild radius. Our observations provide the first direct evidence that a compact radiative source at the center of a galaxy contains of order $10^6$~\msun and provides overwhelming evidence that it is in the form of a super-massive black hole. Finally, the existence of ``intermediate mass'' black holes more massive than $\sim10^4$~\msun between roughly $10^3$ and $10^5$~AU from \sgrab are excluded. \end{abstract} \end{document}