Galaxy Wars: M81 Versus M82

Explanation: In the left corner, wearing a red nucleus surrounded by blue spiral arms, is M81 . In the right corner, sporting light stars and dark dust lanes, is M82 . These two mammoth galaxies have been locked in gravitational combat for the past billion years. The gravity from each galaxy dramatically affects the other during each hundred million-year pass. Last go-round, M82's gravity likely raised circulating density waves rippling around M81 resulting in the richness of M81 's spiral arms. M81, though, left M82 a messy pulp of exploded stars and colliding gas so violent it emits bright X-rays . In both galaxies, colliding gas has created a recent abundance of bright new stars . In a few billion years only one galaxy will remain.