The motion of a star around the central black hole in the Milky Way

The left panel shows an infrared NACO image of a ~ 2 x 2 arcsec 2 area, centred on the position of the compact radio source "SgrA*" at the centre of the Milky Way Galaxy; it is marked by a small cross. The image was obtained in the K s -band at wavelength 2.1 µm in May 2002 and the angular resolution (image sharpness) is about 0.060 arcsec. At about the same time, the star designated "S2" came within 0.015 arcsec of the radio source. At the distance of the Milky Way Center, 1 arcsec on the sky corresponds to 46 light-days; the bar is 20 light-days long (0.44 arcsec). The right panel displays the orbit of S2 as observed between 1992 and 2002, relative to SgrA* (marked with a circle). The positions of S2 at the different epochs are indicated by crosses with the dates (expressed in fractions of the year) shown at each point. The size of the crosses indicates the measurement errors. The solid curve is the best-fitting elliptical orbit - one of the foci is at the position of SgrA* . The 2002 data points come from NACO observations done during the early commissioning, fine adjustement, and Science Verification phases for this instrument