Contact binary star. Image 2 of 2. Computer artwork of the contact binary star W Ursae Majoris (W UMa). This system comprises two stars in a very tight orbit around each other. The stars' atmospheres are in contact, and the friction the contact causes slows the stars' orbits so that eventually they touch, and merge into one star. Before the stars touch, they are individual stars, but after they touch, the stars exchange material freely, becoming practically identical in colour and luminosity. See image R620/261 for this system before the stars touched. W UMa lies around 200 light years away in the constellation Ursa Major (the Great Bear).