Galaxy Wars: M81 versus M82

Explanation: On the right, surrounded by blue spiral arms, is spiral galaxy M81 . On the left, marked by red gas and dust clouds, is irregular galaxy M82 . This stunning vista shows these two mammoth galaxies locked in gravitational combat , as they have been 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 density waves rippling around M81 , resulting in the richness of M81 's spiral arms. But M81 left M82 with violent star forming regions and colliding gas clouds so energetic the galaxy glows in X-rays . In a few billion years only one galaxy will remain .