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Astronomers have observed a rare cosmic phenomenon: about 60 years ago, two massive stars merged to form a binary system. As Robert Lee noted in his article, researchers were able to observe, for the first time, two giant stars orbiting each other while they were still in the process of forming. Using the ALMA (Atacama Large Millimeter/submillimeter Array) radio telescope, scientists tracked the merger of these celestial bodies into a massive star system. It turned out that these stars did not form from a single collapsing cloud of gas and dust, as has traditionally been assumed for most binary systems, but rather came together during their early stages of development.
Because Earth has only one Sun, people are accustomed to thinking of stars as solitary objects. However, approximately half of the Sun-like stars in the Milky Way have a companion, and among massive stars, this figure rises to about 90%. Eventually, such massive stars explode as supernovae, significantly affecting their cosmic surroundings. For this reason, the study of such binary systems is crucial for understanding the evolution of both the stars themselves and galaxies as a whole.
The research team first turned its attention to young, massive protostars in the IRAS 07299−1651 system, located approximately 5,300 light-years away, back in 2019. At first, the scientists saw no signs that these objects had not formed from a single disk-like cloud of material that later disintegrated. However, one significant feature caught their attention: the disks of matter surrounding and feeding the protostars were strangely offset relative to one another.
Over the course of eight years, experts recorded barely perceptible changes in the positions of the stars using the ALMA telescope, the VLA (Very Large Array), as well as infrared images taken with the James Webb Space Telescope and the VLT (Very Large Telescope).
As noted by research team leader Yichen Zhang from Jiao Tong University in Shanghai, China, scientists have for the first time observed two massive stars orbiting each other during their formation. Through their joint efforts, the team was able to reconstruct the complete three-dimensional structure of the IRAS 07299−1651 system, obtaining precise data on the stars’ orbits, the relative positions of their disks, and the angles at which they eject jets into space. Ruben Fedriani, a member of the research team from the Andalusian Institute of Astrophysics in Granada, noted that each telescope provided a unique piece of the overall picture, and the combination of radio and infrared observations provided the greatest possible detail of the formation process of this massive system.
The results came as a complete surprise to the team, as the researchers had expected to see nearly perfect circular orbits. Instead, the orbital trajectories turned out to be extremely elongated or eccentric, resembling parabolas in shape. If the stars had formed from a single gas-and-dust disk, even after its fragmentation, the surrounding disks would have remained parallel to one another. However, in this case, the disks are oriented at sharp angles to one another and to the plane of the stars’ orbits. Another project member, Yao Wang, compared this process to solving a three-dimensional puzzle, where each new observation added another piece, ultimately bringing the orbits, disks, and jets together into a single picture.
It is extremely difficult to explain the chaotic structure of IRAS 07299−1651 using traditional scenarios involving a single disk. Therefore, the researchers proposed a hypothesis according to which both stars formed in separate clouds of gas and dust until a chance encounter brought the young stars and their cocoons into close proximity. By retroactively calculating the orbits, the scientists determined that this fateful event occurred about 60 years ago. On the scale of the universe, where stars exist for billions of years, such a period of time is but a moment. The surrounding gas-and-dust disks were able to withstand this collision, retaining their distinct structures. As Jonathan K. Tan of the Georgia Institute of Technology and the University of Virginia pointed out, the early stages of a star’s life can be extremely chaotic, when a chance encounter escalates into a veritable gravitational dance and a stellar merger.
For now, astronomers cannot definitively say whether these stars are destined to remain neighbors forever or whether they will eventually drift apart in different directions. The system’s ultimate fate remains uncertain, as the continued influence of the surrounding gas could significantly alter its configuration. Researchers hope that new observations of IRAS 07299−1651 will shed light on how events will unfold. At the same time, this long-term monitoring approach opens up new opportunities for science to study young, massive binary systems, which will help determine the prevalence of such random collisions in space.
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