Astronomers discover two stars that joined together to form a binary system just 60 years ago
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Using the ALMA (Atacama Large Millimeter/submillimeter Array) radio telescope, astronomers have watched as two stars come together to form a massive stellar binary. The observations revealed that these stars didn’t form from the same collapsing cloud of gas and dust, as most binary stars are assumed to form, but instead came together later in their infancy.
Here on Earth, we are slightly prejudiced by our single sun to view stars as somewhat solitary bodies. However, around half of sun-sized stars in the Milky Way have a companion star. This percentage of stellar partnership rises to around 90% of massive stars. Eventually, these massive stars go supernova and shape their cosmic surroundings. Thus, understanding these binary systems is vital to our understanding of stars and of galaxies in general.
The team behind this research initially observed the still-growing massive stars, or protostars, in the binary system IRAS 07299−1651, located around 5,300 light-years away in 2019. At first, the researchers didn’t see anything that suggested these stars didn’t form from the same disk-shaped cloud of gas and dust that later fragmented. However, one thing really stood out: the disks of material surrounding and feeding these protostars are oddly misaligned.
Over the course of eight years, the team mapped subtle shifts in the position of the stars using ALMA in addition to the Very Large Array (VLA), as well as infrared images from the James Webb Space Telescope (JWST) and the Very Large Telescope (VLT).
“For the first time, we were able to watch two massive stars move around one another while they were still being born,” team leader Yichen Zhang of Shanghai Jiao Tong University, China, said in a statement.
The team was able to reconstruct the full 3-dimensional structure of IRAS 07299−1651 for the first time, obtaining details about how the stars orbit each other, the way their disks are aligned, and the angle at which they blast jets into space.
“Each telescope revealed a different piece of the puzzle,” team member Rubén Fedriani, of the Instituto de Astrofísica de Andalucía (IAA) in Granada, Spain, said. “The combination of radio and infrared observations provides the most exquisite detail on the formation of this massive protobinary system.”
Unexpected chaos
The team’s observations took them by surprise. They were expecting these stars to orbit each other in neat, near-circular orbits. Instead, the orbits were found to be highly flattened or “eccentric,” almost parabolic.
If the stars had formed from the same disk of material, then even after it fragmented, the individual disks surrounding the stars would be aligned. However, that wasn’t the case; the disks are tilted at a sharp angle to each other and to the orbits of the stars.
“It felt like solving a three-dimensional puzzle,” team member Yao Wang of Shanghai Jiao Tong University said. “Each new observation added another piece, and eventually the orbit, disks, and jets all came together into a single, coherent picture.”
The chaotic structure of IRAS 07299−1651, as observed by the team, is difficult to explain if the two stars emerged from the same disk of material.
Instead, the researchers theorize that the two stars were born in individual clouds of gas and dust, before a chance encounter brought the two infant stars and their respective natal cocoons together.
Tracing back the orbits of the stars, the researchers found that this encounter likely occurred around 60 years ago. Considering stars live for billions of years, that is an instant on a cosmic timescale. The disk-shaped pockets of material around the stars have thus far survived the encounter, retaining their well-defined structures.
“This study demonstrates that the early lives of stars can be quite chaotic, with a chance encounter leading to this gravitational dance and stellar coupling,” team member Jonathan C. Tan of the University of Technology and the University of Virginia said.
What the team can’t yet establish is whether these stars are destined to stick together or if they will eventually move apart. Indeed, this fate may not have been sealed yet; interactions with the surrounding gas could determine what shape this system takes in the future.
The team hopes that further observations of IRAS 07299−1651 will help to better understand what the future holds for these stars.
In the meantime, the long-term monitoring approach adopted by the researchers could provide scientists with a powerful new way of investigating other young massive binary systems. This could reveal how common encounters like this are and if more binary systems are composed of stars brought together by chance encounters.
The team’s research was published on Tuesday (Sept. 8) in the journal Nature Astronomy.
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