Contents -- Preface -- 1. Observational Techniques -- 1.1 The GC Across the Electromagnetic Spectrum -- 1.1.1 Radio Wavelengths -- 1.1.2 Far-Infrared Wavelengths -- 1.1.3 Near- and Mid-Infrared Wavelengths -- 1.1.4 Optical Wavelengths -- 1.1.5 X-Ray Energies -- 1.1.6 y-Ray Energies -- 1.2 NIR Imaging Through the Atmosphere -- 1.3 Speckle Imaging -- 1.3.1 The Knox-Thompson Method -- 1.3.2 The Bispectrum Analysis -- 1.3.3 Seeing Calibration of Fourier Data -- 1.3.4 The Shift-and-Add Algorithm -- 1.3.5 Speckle Spectroscopy -- 1.3.6 Speckle Instrumentation -- 1.3.6.1 SHARP -- 1.3.6.2 NIRC -- 1.4 Single Telescope Adaptive Optics -- 1.4.1 Adaptive Optics Imaging -- 1.4.2 Adaptive Optics Spectroscopy -- 1.4.3 Adaptive Optics Instrumentation -- 1.4.3.1 NAOS/CONICA -- 1.4.3.2 NIRC2 -- 1.4.3.3 PUEO -- 1.4.3.4 ADONIS -- 1.4.3.5 HOKUPA'A -- 1.4.3.6 FASTTRAC -- 1.5 Cleaning and Deconvolution -- 1.5.1 Linear Deconvolution -- 1.5.2 Lucy-Richardson Deconvolution -- 1.5.3 Estimating the PSF -- 1.5.4 Iterative Blind Deconvolution -- 1.5.5 Comparison of Deconvolution Algorithms -- 1.6 Future IR Interferometry -- 1.6.1 VLTI -- 1.6.2 Keck Interferometer -- 1.6.3 LBT LINC/NIRVANA -- 2. Observational Results -- 2.1 The Discovery of Sagittarius A -- 2.2 Large-Scale Structures at the Galactic Center -- 2.3 The Circum Nuclear Disk -- 2.4 The Mini-Spiral -- 2.5 Radio Filaments -- 2.6 Near-lnfrared Images of the Central Stellar Cluster -- 2.6.1 A Brief History of NIR Imaging -- 2.6.2 Diffraction Limited Images -- 2.7 The Radio and lnfrared Positional Reference Frames -- 2.8 Number Density Counts -- 2.8.1 Evidence for a Central Stellar Cusp -- 2.8.2 K-band Luminosity Function -- 2.9 Polarization of Filaments and Stars -- 2.9.1 Extended Filaments in the Sgr A Complex -- 2.9.2 Polarized Emission from Stars -- 2.10 Stellar Velocities and Orbital Accelerations.

2.10.1 Measuring Stellar Proper Motions -- 2.10.2 Motions in the Outer Cluster -- 2.10.3 Motions in the Inner Cluster -- 2.10.4 Accelerations of Stars Near Sgr A -- 2.10.5 Stellar Orbits -- 2.11 Spectroscopy -- 2.11.1 Stellar Populations -- 2.11.2 The Upper Mass Cut-Off -- 2.11.3 The Central Arcsecond -- 2.11.4 Results of Speckle Spectroscopy -- 2.11.4.1 Extraction and Calibration of Spectra -- 2.11.4.2 Spectra in the Central Sgr A* Cluster -- 2.11.5 Adaptive Optics Spectroscopy of the Central Cusp -- 2.12 Star Formation at the Galactic Center? -- 2.12.1 Embedded Objects -- 2.12.2 IR-Excess Objects -- 2.13 Sgr A* Across the Electromagnetic Spectrum -- 2.13.1 Size and Spectrum of Sgr A* at Radio Wavelengths -- 2.13.2 Polarization of Sgr A* at Radio Wavelengths -- 2.13.3 Sgr A* as a Variable X-Ray Source -- 2.13.4 Sgr A* as a Variable NIR Source -- 2.13.5 How Likely are Strong NIR Flares? -- 2.13.6 First Simultaneous X-Ray/NIR Detection of Sgr A* -- 3. Astrophysical Results -- 3.1 The Stellar Velocity Field -- 3.2 Scenarios for Star Formation at the Galactic Center -- 3.2.1 Infall of Stellar Clusters -- 3.2.2 In Situ Formation from Dense Gas -- 3.2.3 Formation of Stars in the Mini-Spiral -- 3.2.4 Capture of Stars by Ejection of Stellar Remnants -- 3.3 The Central Dark Mass -- 3.3.1 First Order Estimates -- 3.3.2 Mass Estimators -- 3.3.3 The Jeans Method -- 3.3.4 The Orbit of the Star S2 -- 3.3.5 Orbits of Other Stars Around Sgr A* -- 3.3.6 A Lower Limit to the Mass -- 3.4 Stability of the Enclosed Dark Mass -- 3.5 Agglomerations of Exotic Particles? -- 3.6 The Central Stellar Cusp -- 3.6.1 Spatial Distribution of the Stars -- 3.6.2 Velocity Distribution of the Stars -- 3.6.3 Mass of the Cusp -- 3.6.4 Young, Massive Stars in the Cusp -- 3.6.5 Dynamics of the Cusp and Presence of Young Stars -- 3.7 Analysis of Stellar Orbits Near the Central Black Hole.

3.7.1 Relativistic Periastron Shift -- 3.7.2 Lense-Thirring Precession -- 3.7.3 Newtonian Effects -- 3.7.4 Orbits in a Uniform Density Sphere -- 3.7.5 Stellar Deflections -- 3.7.6 Constraints from non-Keplerian Orbits -- 3.8 The Central Black Hole -- 3.8.1 Standard Accretion Theory -- 3.8.2 The Low Luminosity of Sgr A* -- 3.8.3 Radiatively Inefficient Accretion Flow Models -- 3.8.4 Sgr A* Flare Models -- 3.8.5 A Spin Measurement of the Black Hole? -- 3.8.6 Gravitational Disk Modes -- 3.8.7 Imaging the Event Horizon of Sgr A* -- 3.9 Comparison to Nuclei of Other Galaxies -- 3.10 Massive Black Holes at High Redshifts -- Appendix A Color Versions of Selected Figures -- Appendix B Table of Individual Sources -- Appendix C Useful Quantities -- Appendix D Table of Abbreviations -- Bibliogruphy -- Index.