The visible disk and spiral arms of NGC 2442 span about 150,000 light years. The asymmetric structure of NGC 2442 with its strong drawn out northern arm (left) and weaker, more loosely defined southern arm are likely the result of a previous tidal interaction with a galaxy not seen in the image. The northern arm which appears to be bent back on itself is producing more than its share of star forming regions likely triggered by gravitational interplay with another massive structure. Ryder et al. (APJ 2001) identified a nearby intergalactic gas cloud containing nearly 1/3 the amount of atomic hydrogen as NGC 2442 itself. Astronomers believe that the cloud which contains the mass of a billion suns was violently stripped from NGC 2442 during an intergalactic tug of war. NGC 2442 has a pronounced central bar and the southern arm has a peculiar "hook" shape which is why some refer to it as the "Meathook" galaxy.
Simulation of an intergalactic interaction with NGC 2442 and its northern arm formation
NGC 2442: Tidal Encounters and the Evolution
of Spiral Galaxies
J. Christopher Mihos
Department of Physics and Astronomy,
Johns Hopkins University, Baltimore, MD 21218