Contact binary star. Image 1 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, merging into one star. After they touch, the stars exchange material freely, becoming practically identical in colour and luminosity. See image R620/262 for this system after the stars touch. W UMa lies around 200 light years away in the constellation Ursa Major (the Great Bear).