Header image: ESO/T. Preibisch

Whether most stars form in clusters is an age-old question in star formation. Traditionally, it was assumed that all stars form in open clusters, and as these clusters disrupt, stars become unbound from their formation cluster and disperse into their host galaxy. More recent observations cast doubt on that, however — suggesting that most clusters did not form in clusters.

Well, the picture just got a lot clearer: when using the latest cluster and OB star catalogues and doing corrections for the incompleteness of both catalogues (which is critical!), it seems that most stars did form in clusters. Our short new letter accepted in A&A and led by Alexis Quintana at the Paris Observatory came out today!

We estimate that at least 50% of stars formed in ‘compact’ clusters, but probably more than 80%. This is much higher than previous recent estimates, which usually put the number at 15-35%. However, given that significantly more clusters are now known, and we now have better estimates of their parameters (especially masses), this maybe isn’t surprising.

Long-term, we expect this result to have some impact on models of star formation. While it’s likely that many small, compact clusters disperse very quickly, probably on the order of ~10 million years (that’s quick in astronomy…), our results are incompatible with other recent models and works on star formation that proposed almost all stars form hierarchically, and with a preference for isolated star formation. In reality, the true picture is probably somewhere in-between: stars form in clusters (the traditional model), but those clusters undergo complicated formation processes that are often hierarchical, intertwined, and turbulent.