Astrophys. J. 704, 324–340 (2009)

When galaxies merge, the gravitational jostling of gases can lead to a bump in the galaxies' star formation rate. But this effect is short-lived and does not significantly add to overall star numbers, say Aday Robaina of the Max Planck Institute for Astronomy in Heidelberg, Germany, and his colleagues.

In analysing images of 2,551 galaxies from the Spitzer and Hubble space telescopes, the researchers found that merging and closely interacting galaxies gave birth to stars at rates only 1.8 times higher than non-interacting galaxies — a smaller effect than previously thought. For the portion of the Universe between about 1 billion and 2 billion parsecs away, the researchers estimate that only about 8% of star births are triggered by galaxy mergers.