Physical conditions, dynamics, and mass distribution in the center of the Galaxy

This review emphasizes recent investigations of the central 10 pc of the Galaxy and conclusions on energetics, dynamics, and mass distribution derived from them. New information on the Galactic center comes from X­ and gamma-ray measurements and from infrared and microwave studies, especially from spectroscopy, high-resolution imaging, and interferometry. Section 2 is an overview of the phenomena seen in the Galactic center. In Section 3 we cover the questions of energetics and luminosity, followed by a discussion of the distribution, excitation, and dynamics of the neutral and ionized interstellar matter in Sgr A (Section 4): Our current knowledge about the mass distribution and the evidence for and against a massive black hole is analyzed in Section 5, while in Section 6 we discuss the nature of the central 0. 1 pc of the Galaxy. We conclude in Section 7 with a summary. There are other recent reviews on the Galactic center region, and those by Oort (1 977), Lacy et al. ( 1 982), Townes et al. (1983), Brown & Liszt ( 1984), Lo ( 1 986), Genze1 ( 1987), and Serabyn (1 987) are especially relevant for the present discussion. We also refer the reader to the pro-