ALMA is Watching a Massive Binary Star System Form

Most stars in the Milky Way do not exist in isolation. While about 25-30% of M-dwarfs, 45-50% of Sun-like stars, and 50-70% of A-type stars are binaries, that stellar partnership rate climbs steeply for heavy stars, with at least 75%—and potentially more than 90%—of massive O and B-type stars existing within binary or multiple systems. Because these heavy stars shape their surrounding cosmic environments through supernova explosions and the synthesis of heavy elements, understanding how they form is crucial for stellar evolution theory.

Traditionally, astronomers assumed that massive binary stars formed through standard pathways such as disk fragmentation, core fragmentation, or post-formation dynamical capture. However, a team of international researchers tracking the young binary system IRAS 07299−1651 discovered a structural configuration that upends those standard assumptions, revealing an unexpectedly violent origin story captured in real time.

Tracking a Multi-Observatory Campaign on IRAS 07299−1651

The investigation began when researchers first observed the system using the Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope in 2019. Initial data suggested the protostars might have emerged from a single collapsing cloud, but a glaring anomaly immediately caught the team’s attention: the individual disks of gas and dust feeding each forming star were oddly misaligned.

To solve the puzzle, the international team—led by Yichen Zhang of Shanghai Jiao Tong University—committed to nearly eight years of patient observation. They mapped subtle positional shifts by combining ALMA’s high-precision radio data with observations from the Very Large Array, infrared imaging from the James Webb Space Telescope (JWST), and data from ESO’s Very Large Telescope (VLT) tracking jets of material streaming away from the stars.

Photo: BBC Sky at Night Magazine

Betelgeuse Imaging Reveals Turbulent Surface and Persistent Hotspots

“For the first time, we were able to watch two massive stars move around one another while they were still being born.”

Yichen Zhang, corresponding author of the study at Shanghai Jiao Tong University

By bringing together these distinct radio and infrared datasets, the researchers constructed a comprehensive, three-dimensional model of the system. Each facility contributed a vital perspective, allowing scientists to reconstruct orbital trajectories, disk tilts, and the exact spatial orientation of the bipolar jets.

“Each telescope revealed a different piece of the puzzle. The combination of radio and infrared observations provides the most exquisite detail on the formation of this massive protobinary system.”

Rubén Fedriani, co-author of the study at the Instituto de Astrofísica de Andalucía

Uncovering a Parabolic Encounter and Misaligned Disks

When the 3D model finally came together, the structural architecture of IRAS 07299−1651 defied conventional models. Instead of moving along neat, near-circular orbits, the two massive protostars are hurtling along highly flattened, eccentric paths that closely approximate parabolic trajectories.

Photo: Space

Furthermore, the circumstellar gas disks feeding each star are sharply tilted relative to each other and heavily slanted against the plane of their shared orbit. If the stars had formed together through the simple fragmentation of a single rotating disk, their individual rotation axes and surrounding disks would naturally remain aligned. The stark double-tilt rules out standard co-formation.

Betelgeuse Surface Images Reveal Persistent Hotspots and Turbulent Bubbling

“It felt like solving a three-dimensional puzzle. Each new observation added another piece, and eventually the orbit, disks, and jets all came together into a single, coherent picture.”

Yao Wang, first author of the study at Shanghai Jiao Tong University

Rather than being born as a pair, the stars formed independently in separate pockets of gas and dust before a chance gravitational encounter forced them together.

Implications for Stellar Evolution and Future Observations

This rare glimpse into stellar assembly challenges existing frameworks for how tight massive binaries come to be.

“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.”

Jonathan C. Tan, study co-author at the University of Virginia