In the distant star-forming region IRAS 07299−1651, roughly 5500 light-years from Earth, a scene is unfolding that astronomers almost never manage to witness firsthand. Two massive protostars — luminaries not yet fully formed, actively gaining mass from the surrounding gas and dust — are moving around each other. Their combined mass already reaches at least 18 solar masses, and the distance between them is currently about 200 astronomical units. And all of this is happening right now, before our eyes, if one measures by cosmic scales.
An international team of researchers led by Yichen Zhang of Shanghai Jiao Tong University tracked this pair for nearly eight years using the ALMA radio interferometer. They recorded the subtlest shifts in the stars' positions in the sky. To the ALMA data they added observations from the Very Large Array, infrared images from the James Webb telescope and the Very Large Telescope. As a result, they were able to reconstruct a complete three-dimensional picture of the system: the orbit, the orientation of the gas disks around each star, and the direction of the jets streaming out of them.
The picture turned out to be nothing like what they had expected to see. The orbit proved to be highly elongated, almost parabolic. The disks around the two protostars are strongly inclined relative to each other and relative to the plane of the orbit. If the stars had been born together from a single large rotating disk, as the classical fragmentation scenario suggests, their spins and disks should have been roughly coaxial. Here, however, everything looks chaotic and "alien."
The researchers concluded that the two objects began forming independently, in separate dense cores of the molecular cloud. Then a close gravitational encounter occurred — a kind of cosmic "meeting" that took place only about 60 years ago by the earthly calendar. On astronomical clocks, that is an instant. The compact disks around each star survived this encounter and retained their structure. Now the system is balancing on a knife's edge: the orbit lies close to the boundary of the bound state, and further interaction with the surrounding gas may yet decide whether these giants remain together forever or part ways.
This work, published in Nature Astronomy, shows that the early life of massive stars can be far more dynamic and unpredictable than was thought. Most massive luminaries exist in binary or multiple systems, and it is precisely such pairs that later determine the fate of entire regions of space — through supernovae, ejections of heavy elements and the formation of the next generations of stars.
In this event one senses the full scale of the Universe. Somewhere in the cold darkness of an interstellar cloud, two enormous clumps of gas drew close by chance, and out of this encounter a system is being born that may shine for millions of years. We live in a world where such grandiose processes occur constantly, and modern instruments allow us to glimpse for a moment into the very heart of this cosmic ballet.
