Close Encounters of the Second Kind

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Science  04 Jun 2010:
Vol. 328, Issue 5983, pp. 1208
DOI: 10.1126/science.328.5983.1208-b

The Antennae galaxies are the nearest pair of interacting galaxies. As such, they have been extensively studied. Since the early 1970s, numerical simulations of the Antennae have successfully reproduced the system's large-scale morphology, with two long tidal tails and two distinct galactic disks, but they have failed to account for the observed high rate of star formation occurring in the overlap region between the two merging galaxies. Now, a model by Karl et al. can account for this off-nuclear burst of star formation if the two galaxies are assumed to have had a second encounter 40 million years ago, after a first close passage 600 million years ago. In this timeline, the first passage comes much earlier than predicted by previous models—which implicated only a single close encounter—and puts the system in a later merger phase. The model predicts that the observed starburst has a very short lifetime as compared to the full merging process. This may explain why off-nuclear starbursts are rarely seen in interacting galaxies.

Astrophys. J. 715, L88 (2010).

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