The stellar nurseries of distant galaxies

An international team headed by UNIGE has discovered that the properties of molecular clouds, and the number of stars they produce, are different depending on whether they are in distant or nearby galaxies. Star clusters are formed by the condensation of molecular clouds, masses of cold, dense gas that are found in every galaxy. The physical properties of these clouds in our own galaxy and nearby galaxies have been known for a long time. But are they identical in distant galaxies that are more than 8 billion light-years away? For the first time, an international team led by the University of Geneva (UNIGE) has been able to detect molecular clouds in a Milky Way progenitor, thanks to the unprecedented spatial resolution achieved in such a distant galaxy. These observations density and internal turbulence than the clouds hosted in nearby galaxies and that they produce far more stars. The astronomers attribute these differences to the ambient interstellar conditions in distant galaxies, which are too extreme for the molecular clouds typical of nearby galaxies to survive. Molecular clouds consist of dense, cold molecular hydrogen gas that swirls around at supersonic velocities, generating density fluctuations that condense and form stars. In nearby galaxies, such as the Milky Way, a molecular cloud produces between 10+3 and 10+6 stars. In far-off galaxies, however, located more than 8 billion light-years away, astronomers have observed gigantic star clusters containing up to 100 times more stars. Why is there such a difference?