Astronomy Picture of the Day

Explanation: 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 galaxyM82. 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 galaxydramatically affects the other during each hundred-million-year pass. Last go-round, M82's gravity likely raiseddensity waves rippling around M81, resulting in the richness of M81'sspiral arms. But M81 left M82 withviolent star forming regions and colliding gas clouds so energetic the galaxyglowsin 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 galaxywill remain.