This is an infrared image, centred on the position of the compact radio source SgrA* at the centre of the Milky Way Galaxy. The image was obtained in the Ks-band at wavelength 2.1 m in May 2002 by the NACO camera on one of the European Southern Observatory's VLT telescopes.
As the image was taken, the star S2 came within about 17 light-hours of SgrA*.
The chart displays the orbit of S2 between 1992 and 2002, relative to SgrA*. The positions of S2 at the different epochs are indicated by crosses with the dates 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. Other data comes from the 3.5-m New Technology Telescope (NTT) at the ESO La Silla Observatory, Chile and the 10-m Keck telescope, Hawaii, USA.
That data indicates that there is a black hole, around 3 million times more masssive than the Sun, at the center of galaxy.