Galaxy Wars: M81 versus M82.

In the upper left corner, surrounded by blue arms and dotted with red nebulas, is spiral galaxy M81 . In the lower right corner, marked by a light central line and surrounded by red glowing gas, 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 . This big battle is seen from Earth through the faint glow of an Integrated Flux Nebula , a little studied complex of diffuse gas and dust clouds in our Milky Way Galaxy . In a few billion years, only one galaxy will remain .