The central region of our Galaxy, which cannot be seen optically because it is obscured by dense concentrations of dust. Radio and infrared observations reveal a complex environment dominated by the radio source Sagittarius A. The compact radio source Sagittarius A* appears to mark the central point and is used as the origin for galactic coordinates. Within ten light years of the centre there is a ring of gas and dust, rotating at about 110 km/s and surrounding a massive object, probably a black hole, of 4 million solar masses.