Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006jphcs..54.....s&link_type=abstract
"Journal of Physics: Conference Series, Volume 54, Proceedings of "The Universe Under the Microscope - Astrophysics at High Angu
Astronomy and Astrophysics
Astrophysics
Scientific paper
We are pleased to present the proceedings from the Galactic Center Workshop 2006—From the Center of the Milky Way to Nearby Low-Luminosity Galactic Nuclei. The conference took place in the Physikzentrum, Bad Honnef, Germany, on 18 to 22 April 2006. It is the third workshop of this kind, following the Galactic Center Workshops held 1998 in Tucson, Arizona, and 2002 in Kona, Hawaii.
The center of the Milky Way is the only galactic nucleus of a fairly common spiral galaxy that can be observed in great detail. With a distance of roughly 8 kpc, the resolution that can currently be achieved is of the order 40 mpc/8000 AU in the X-ray domain, 2 mpc/400 AU in the near-infrared, and 0.01 mpc/1 AU with VLBI in the millimeter domain. This is two to three orders of magnitude better than for any comparable nearby galaxy, making thus the center of the Milky Way thetemplate object for the general physical interpretation of the phenomena that can be observed in galactic nuclei.
We recommend the summary article News from the year 2006 Galactic Centre workshopby Mark Morris and Sergei Nayakshin—who also gave the summary talk of the conference—to the reader in order to obtain a first, concise overview of the results presented at the workshop and some of the currently most exciting—and debated—developments in recent GC research.
While the workshops held in 1998 and 2002 were dedicated solely to the center of the Milky Way, the field of view was widened in Bad Honnef to include nearby low-luminosity nuclei. This new feature followed the realization that not only the GC serves as a template for understanding extragalactic nuclei, but that the latter can also provide the context and broader statistical base for understanding the center of our Milky Way. This concerns especially the accretion and emission processes related to the Sagittarius A*, the manifestation of the super massive black hole in the GC, but also the surprising observation of great numbers of massive, young stars in an environment that was previously thought hostile to star formation.
Highlights of the GC Workshop 2002 in Kona were certainly the extraordinary evidence for the black hole nature of Sagittarius A* provided by the observation of orbits of individual stars around the central dark mass of the Milky Way, and the observations of short radiation outbreaks from Sgr A* in the X-ray regime, the so-called flares. These events with their variability on the minute time scale provided additional hard evidence for the black hole nature of Sgr A*. Also, the new observational capabilities provided by Chandraand XMMprovided spectacular new insights into the physics of the GC.
With the black hole nature of Sagittarius A* now confirmed beyond reasonable doubt, theory and observation are zooming into ever smaller scales, trying to understand the exact physics behind the extreme under-luminosity (10-9 10-10 in terms of Eddington luminosity) of Sagittarius A*. Especially observations of the submm, NIR, and X-ray flares appear to be promising sources to analyze the accretion physics of Sagittarius A* near its event horizon. Some flares may carry the actual imprint of plasma moving at relativistic velocities near the last orbit of the black hole. Another topic that has moved into the focus of attention is star formation near the central black hole. One, possibly two, disks of young massive stars in the central half parsec, generally assumed hostile to star formation, challenge current theories of star formation. Through new infrared integral field spectrometers there is now strong evidence that the stars in the immediate environment of Sagittarius A*, the so-called S-stars are B-type main sequence stars. There are many hypothesis for their origin, but no model could yet provide entirely satisfactory explanations for their existence.
A significant number of new telescopes and instruments access ever greater detail at all wavelengths. The continuing development of (sub)-millimeter instrumentation, for example, provides high spatial resolution as well as important spectroscopic data on the complex chemistry of the central tens of parsecs. The new X-ray satellite Suzaku delivers unprecedented spectral resolution in the X-ray domain. Instruments such as H.E.S.S. open, for the first time, the window toward observations in the TeV regime with sub-arcminute resolution. A spectacular near-to-mid-infrared survey of the central hundred parsecs of the Milky Way has been conducted with the Spitzer infrared satellite. VLBI is moving to ever shorter wavelengths, opening the tantalizing prospect of imaging processes near the event horizon of Sagittarius A* within the next decade. Finally, the brightest near- and mid-infrared sources in the central parsec have been and are continued to be examined with infrared interferometry at the ESO Very Large Telescope Interferometer. These first observations clear the way for future ambitious measurements of relativistic effects in the immediate environment of the black hole.
The articles in this volume can also be accessed on-line in electronic form, including full color figures and multimedia files. The proceedings can be accessed via the internet site of the Journal of Physics: Conference Series of Institute of Physics Publishing. A link to this site can be also found on the web site of the GC 2006 Workshop, http://www.ph1.uni-koeln.de/GC06. The complete program of the conference, pictures, and other material can be accessed via this site as well.
We are grateful to everyone who helped with their efforts to make this conference a fruitful and enjoyable one. Special thanks to the LOC and to the employees of the Physikzentrum in Bad Honnef. The location proved to be a perfect choice, providing all the necessary infrastructure on a high level, a fantastic lecture hall, and the very comfortable basement hall for discussing and socializing in the evenings. We also would like to thank all people working as editors for GCNEWS—The Galactic Center Newsletter, who helped with their know-how from previous GC workshops. GCNEWS is a newsletter that appears several times each year with articles and news on the Galactic Center, including abstracts of recently published papers. Please see http://www.aoc.nrao.edu/~gcnews for further information. GCNEWS is a communication platform for the steadily increasing community of GC researchers and is the backbone behind the GC Workshops.
We acknowledge financial support for the conference by the Deutsche Forschungsgemeinschaft (DFG)Sonderforschungsbereich project number SFB 494.
Finally, we would like to thank the more than 100 participants of the GC Workshop 2006 for their enthusiasm and the numerous active contributions which made this conference such a success.
Rainer Schödel, Geoffrey C Bower, Michael P Muno, Sergei Nayakshin and Thomas Ott Editors
The PDF file contains various photographs taken at the conference and the conference schedule.
Bower Geoffrey C.
Muno Michael P.
Nayakshin Sergei
Ott Thomas
Schödel Rainer
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