Related papers: The Proper Motion of SgrA*: I. First VLBA Results

We report measurements with the VLBA of the position of Sgr A* 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 +/- 0.024 mas/y along a…

We report measurements with the Very Long Baseline Array of the proper motion of Sgr A* relative to two extragalactic radio sources spanning 18 years. The apparent motion of Sgr A* is -6.411 +/- 0.008 mas/yr along the Galactic plane and…

Sagittarius A* (Sgr A*) is a strong, compact radio source believed to be powered by a super-massive black hole at the galactic center. Extinction by dust and gas in the galactic plane prevents observing it optically, but its position and…

Proper motions and radial velocities of luminous infrared stars in the galactic center have provided strong evidence for a dark mass of 2.5 million solar masses in the central 0.05 pc of the galaxy. The leading hypothesis for this mass is a…

We report progress on measuring the position of Sgr A* on infrared images, placing limits on the motion of the central star cluster relative to Sgr A*, and measuring the proper motionof Sgr A* itself. The position of Sgr A* has been…

We measure the proper motion of the pulsar PSR J1745-2900 relative to the Galactic Center massive black hole, Sgr A*, using the Very Long Baseline Array (VLBA). The pulsar has a transverse velocity of 236 +/- 11 km s^-1 at position angle 22…

The absolute position of the compact radio source at the dynamical center of the Galaxy, Sgr A$^*$, was known only to an accuracy of $0.2''$ in spite of its accurate location with respect to near-IR stellar sources to within 30…

Over a two year period (1995-1997), we have conducted a diffraction-limited imaging study at 2.2 microns of the inner 6"x6" of the Galaxy's central stellar cluster using the Keck 10-m telescope. The K band images obtained reveal a large…

We present proper motions for $>$40 stars at projected distances $\leq1.2''$ from Sagittarius A* (Sgr A*). We find evidence on a $\geq2\sigma$ level for radial anisotropy of the cluster of stars within $1''$ of Sgr A*. We find no evidence…

We present 7 mm lambda VLBA observations of the compact nonthermal radio source in the Galactic Center, Sgr A*. These observations confirm the hypothesis that the image of Sgr A* is a resolved elliptical Gaussian caused by the scattering of…

We show that observations by Backer and collaborators over the past two decades constrain the time derivative of the proper motion of Sgr A* to be less than 0.14 mas yr^{-2}. Using this result and a preliminary measurement by Eckart and…

We report here on multi-frequency VLBA observations of three extragalactic sources within 1 degree of the Galactic Center. These sources have been used as astrometric reference sources for VLA and VLBA determinations of the proper motion of…

We successfully measured the trigonometric parallax of Sagittarius A* (Sgr A*) to be $117\pm17$ micro-arcseconds ($\mu$as) using the VLBI Exploration of Radio Astrometry (VERA) with the newly developed broad-band signal-processing system…

We present 44 and 226 GHz observations of the Galactic center within 20$"$ of Sgr A*. Millimeter continuum emission at 226 GHz is detected from eight stars that have previously been identified at near-IR and radio wavelengths. We also…

We study the environment of Sgr A* using spectral and continuum observations with the ALMA and VLA. Our analysis of sub-arcsecond H30alpha, H39alpha, H52alpha and H56alpha line emission towards Sgr A* confirm the recently published broad…

Because of its particular orientation around the Galaxy - i.e., in a plane nearly perpendicular to the Galactic plane and containing both the Sun and Galactic center - the Sagittarius (Sgr) stream provides a powerful means by which to…

For very fast spinning black holes with a>0.9953 the orbital velocity of a test particle unexpectly shows a positive radial gradient for low orbits, an effect of GR which has been overlooked so far. For a=0.99616 the maximum radial change…

We present new proper motion measurements and simultaneous orbital solutions for three newly identified (S0-16, S0-19, and S0-20) and four previously known (S0-1, S0-2, S0-4, and S0-5) stars at the Galactic Center. This analysis pinpoints…

Predictions from a Galactic Structure and Kinematic model are compared to the absolute proper-motions of about 30,000 randomly selected stars with $9 < B_{\rm J} \le 19$ derived from the Southern Proper-Motion Program (SPM) toward the South…

The compact radio source Sgr A* is coincident with a 4 million solar mass black hole at the dynamical center of the Galaxy and is surrounded by dense orbiting ionized and molecular gas. We present high resolution radio continuum images of…