It is one of the main unsolved problems in astrophysics to determine the physical mechanisms driving star formation. A team of scientists led by Diederik Kruijssen at Heidelberg University and Andreas Schruba at the Max Planck Institute for Extraterrestrial Physics has now managed for the first time to reconstruct the time-evolution of interstellar clouds of gas and dust, so called molecular clouds, and the star formation process within them. Using new observations of the spiral galaxy NGC300, the team was able to demonstrate that star formation proceeds very rapidly, yet is highly “inefficient”. Most of the interstellar gas is not converted into stars, but is instead dispersed by stellar radiation. Molecular clouds are short-lived structures undergoing rapid lifecycles, driven by the intense radiation from the new-born stars within them. This finding shows that galaxies consist of building blocks that flicker as sparkles in fireworks constantly change their appearance.
Star formation in molecular clouds can be explained in two ways. Molecular clouds may be long-lived, and eventually convert all of their gas into stars. In this case, young stars should be found within the molecular clouds from which they have formed. Alternatively, stars may form rapidly and their intense radiation may quickly disperse their birth cloud, causing only a small fraction of the gas to be converted into stars. In this case, young stars and molecular clouds should be generally displaced and coincide only during the short period of star formation.