Talk detail

Participant	Gillessen, Stefan
Institution	MPE - Giessenbachstrasse - Garching - Bavaria - Germany

Session	TC1	Accepted		Order	Time
Talk	Oral abstract	Title	The black hole at the Galactic Center
Co-authors
Abstract	Since the discovery of the non-thermal, compact radio source Sgr A* it has been suspected that the center of the Milky Way harbors a massive black hole. A breakthrough in measuring the associated mass became possible with the advance of infrared astronomy. Within a decade the observations have progressed from velocity dispersion arguments to tracking individual stars as test particles for the gravitational potential. Technically this was possible due to high- angular resolution techniques, in particular adaptive optics, at very large telescopes. Today, the 4 million solar masses black hole in the Galactic Center is the best case for the existence of an astrophysical black hole in general. For more than twenty stars orbits have been determined and further progress can be expected - both from the ever growing time base as well as from future techniques such as near-infrared interferometry. Equally fascinating are the flares occurring a few times per day, during which Sgr A* shines up in the infrared and X-ray domain. The emission is due to a population of transiently heated electrons in the innermost zone of the accretion flow onto Sgr A*. With the advent of near-infrared interferometry in the future, such events could be used as tracers for the space-time around the massive black hole.

Session	EG4	Accepted		Order	Time
Talk	Oral abstract	Title	Observing stellar motions at the Galactic center
Co-authors
Abstract	The Galactic Center allows for unparalleled observations of a dense nuclear star cluster around a massive black hole. Using adaptive optics on a very large telescope is the key to resolving the individual stars down to milli-parsec scales. Thousands of proper motions, hundreds of radial velocities and dozens of accelerations have been measured to date. These data show that the Galactic Center is in a surprisingly complex dynamic state. First, there is a population of young B stars that orbit the black hole at small radii where these stars cannot have formed. Second, a population of massive O/WR stars from a recent star formation event orbits the centre in a disk-like configuration. And third, the population of old giants does not follow a radial cusp profile, questioning whether the system is relaxed at all.