ESA’s Herschel infrared satellite telescope has clarified the circumstances for rapid star formation in galaxies. In the present (nearby) universe, rapid star formation is observed only in galaxies that have experienced collisions with other galaxies. However, the new findings make it clear that such collisions aren’t necessary for rapid star formation. By careful study of the spectra of much more distant galaxies – which are seen as they were at an earlier time in the universe – it’s been shown that the rate of star formation is directly proportional to the amount of interstellar gas contained in galaxies not undergoing collisions. Since nearby galaxies are significantly older, they have already used up most of their interstellar gas, and only the disturbance caused by a collisions is sufficient to reinvigorate the rate of star formation.
Gas is the raw building material for stars and this work reveals a simple link: the more gas a galaxy contains, the more stars are born.
“It’s only in those galaxies that do not already have a lot of gas that collisions are needed to provide the gas and trigger high rates of star formation”, says Dr Elbaz.