ESA Science & Technology - Artist's impression of a galaxy forming stars in a gentle and steady fashion

This illustration shows a galaxy which is accreting mass from rapid, narrow streams of cold gas. These filaments provide the galaxy with a continuous flow of raw material to support its star-forming activity at a rather leisurely pace.

This theoretical scenario for galaxy formation is based on the numerical simulations presented by Dekel et al., 2009 (Nature, 457, 451D). However, the actual process of stream accretion onto a galaxy has never been directly observed to date and the scenario remains only speculative.