Researchers unravel mystery behind birth of triple star system

An international research team led by Professor Jeong-Eun Lee from Seoul National University has uncovered the mysterious origins of triple star systems. Using the Atacama Large Millimeter/submillimeter Array (ALMA), the team delved into the intricate gas structure surrounding protostars in the triple system known as IRAS 04239+2436.

In their groundbreaking study, they detected radio signals of sulfur monoxide (SO) molecules acting as cosmic breadcrumbs, leading the researchers to the discovery of three colossal spiral arms. These arms were found to serve as 'streamers' - cosmic conveyor belts transporting material to the newborn stars.

Through a combination of observations and numerical simulations led by Professor Tomoaki Matsumoto from Hosei University, the team unraveled the mysterious origins of these streamers, providing a breakthrough in our understanding of star formation.

Understanding the mechanism behind the formation of multiple stars is crucial for developing a comprehensive theory of star formation. While several scenarios have been proposed, the exact process has remained elusive. Observing the critical moment when multiple protostars are born is a challenging task that demands cutting-edge technology with high resolution and sensitivity. ALMA's unique capabilities make it the ideal tool for peering into these complex star forming regions.

The ALMA observations of the young trinary protostar system revealed that the distribution of SO molecules forms large spiral arms extending up to 400 astronomical units. They also measured the velocity of the gas containing SO molecule. By analyzing the gas motion in these arms, the researchers confirmed that they are the streamers that supply gas to the triple protostars.

"My first impression was that the structures were dancing together, spinning around the central protostellar system, although we later found that the spiral arms are channels of material feeding the baby stars," says Lee.

Further, the team compared the observed gas velocity with numerical simulations using supercomputers dedicated to astronomy in the Center for Computational Astrophysics at the National Astronomical Observatory of Japan (NAOJ). The simulations modelled three protostars forming in the gas cloud, showing that the spiral arms are formed as a result of gas disturbances around the triple protostars.

Unlike the previously proposed turbulent fragmentation and disk fragmentation scenarios for the formation of multiple stars, the research team explained the triple protostar observed here by a hybrid scenario that combines both aspects. In this hybrid model, the star formation process begins as a turbulent natal gas cloud, which eventually produces the seeds for new protostars in a disk-like structure. The surrounding gas turbulence then extends the spiral arms widely, resulting in the formation of the triple protostar system.

The similarity between the observational and simulation results suggests that the observed triple protostars are the first objects confirmed to demonstrate the formation of multiple stars by a hybrid scenario.

"The actual observation of a multi-star system in formation through the hybrid scenario will significantly contribute to resolving debates over multiple star formation scenarios. Furthermore, this research confirmed the recently noticed streamers' existence and explained how they formed, marking a significant advancement," Matsumoto concluded.