Galaxy Wars: M81 versus M82 . ... Credit Copyright: Leonardo Orazi 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. ... Last go-round, M82 's gravity likely raised density waves rippling around M81 , resulting in the richness of M81 's spiral arms. ...