Milky Way galactic centre. Chandra X-ray Observatory (CXO) image of nebulae (red, yellow and blue clouds) and star clusters (groups of blue dots) in the central region of the Milky Way galaxy. The blue dots are hot young stars, emitting X-rays. The X-ray sources are ionizing the surrounding gas and dust, causing them to heat up and emit X-rays of varying energy from red/yellow to blue. Three star clusters are seen here: the Arches (upper right); the Quintuplet (upper centre) and the GC Cluster (lower centre). The bright X-ray source behind the GC Cluster is the galactic centre itself. The centre of the Milky Way galaxy is about 25,000 light years from Earth, in the constellation Sagittarius.