Massive stars much bigger than our sun always come in pairs or groups, not alone. But astronomers don’t fully understand how these groupings form. In a new study, astronomers using ALMA have serendipitously discovered a young system containing nine baby stars forming together, and they have detailed a rare glimpse of the formation of such a stellar family in its earliest assembly stage in a paper submitted to the arXiv preprint server on June 2.

There are a few competing theories of how groups of stars form: disk, core and filament fragmentation. That is, a spinning disk of gas around a young star breaks apart into multiple pieces, or a big core of gas fragments into multiple star-forming clumps before the stars even form, or a long filamentary cloud of gas breaks into clumps along its length, each clump forming a star.

Massive stars, growing together as a group, are hard to study because they are far away, buried in thick dust and grow up fast while still in dense clouds. So astronomers have not caught many of them “in the act” of forming.