ASTRONOMY PICTURE

OF THE DAY

MARCH 25, 2008

Galaxy Wars: M81 versus M82

EXPLANATION

On the left, surrounded by blue spiral arms, is spiral galaxy M81. On the right 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.

Credit

Rainer Zmaritsch & Alexander Gross