Astrophys. J. 692, 298–308 (2009)

Most astronomers agree that spiral galaxies, which were dominant billions of years ago, morphed into the lens-shaped galaxies that are so prevalent today. One idea describing how this happened assumes the existence of regions of hot gas in the intergalactic space of massive galaxy clusters. The hot gas strips away gas in spiral galaxies as they whip through the intergalactic space, turning them into lenticulars.

But David Wilman of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, and his colleagues have observed lenticular galaxies forming as easily in sparse groups of galaxies, in which the stripping effect of hot gas is negligible. This suggests that, as some astronomers had suspected, galactic mergers are instead an important mechanism.