A study led by Paolo Padoan, ICREA research professor at the Institute of Cosmos Sciences at the University of Barcelona, is challenging long-held beliefs about the formation of planetary disks around young stars. The research, which was published on April 21st in Nature Astronomy, reveals that the environment plays a crucial role in determining the size and lifespan of these disks, which are the birthplaces of planets.
When a star forms, it is surrounded by a spinning disk of gas and dust. Over time, this material coalesces into planets. Traditionally, scientists believed that once a disk forms, it simply loses mass over time as it fuels the growing star and planets. However, Dr. Padoan's research introduces a new perspective, showing that young stars actually gain mass from their surroundings through a process known as Bondi-Hoyle accretion. This process helps "refuel" the disk, making it larger and longer lasting than previously thought.
"Stars are born in groups or clusters inside large gas clouds and can remain in that environment for a few million years after their birth," said Dr. Padoan, first author of the study. " After a star is formed, its gravity can capture more material from the parental gas cloud, not enough to change the star’s mass significantly, but more than enough to restructure its disk. To understand how much mass a star can attract with this Bondi-Hoyle accretion, and the disk spin and size induced by the new material, we needed to model and understand some fundamental properties of the chaotic motion of the interstellar gas, known as turbulence. "
The study demonstrates that Bondi-Hoyle accretion can supply not only the mass but also the angular momentum necessary to explain the observed sizes of protoplanetary disks. This revised understanding of disk formation and evolution alleviates several longstanding observational discrepancies and compels substantial revisions to current models of disk and planet formation.
The research also addresses several puzzles in star and planet formation, such as why more massive stars have larger disks, why some planetary systems are unexpectedly massive, and why some disks last longer than expected. By shifting the focus from the star itself to the wider environment, this research provides a fresh perspective on the cosmic recipe for star and planet formation.
Dr. Padoan's team used advanced computer simulations and analytical modelling to explain the size of protoplanetary disks measured by ALMA, the world's most powerful radio telescope. The combination of theoretical models and empirical data provided a robust framework for understanding the complex interactions between young stars and their environments.
"Comparing the observable data from simulations to the actual observations is essential in validating the simulations, " said Dr. Veli-Matti Pelkonen, ICCUB researcher and member of the team. "However, simulations allow us to go beyond the observables to the underlying density, velocity and magnetic field structures, as well as following them in time. In this study, using the simulation data, we were able to show that the Bondi-Hoyle accretion plays an important part of the late-stage star formation, increasing the lifespan and the mass reservoir of the protoplanetary disks. With the increase of the computing power of supercomputers, we will be able to model even more complex physical processes in the simulations, further increasing the fidelity of the simulations. Combined with the new, powerful telescopes such as the James Webb Space Telescope and ALMA doing unparalleled observations of newly forming stars, these advances will continue to increase our understanding of star formation."
The implications of this study extend beyond just the formation of stars and planets. Understanding the role of the environment in disk formation could also shed light on the conditions necessary for the formation of habitable planets. This could have profound implications for the search for life beyond our solar system.
Reference: Padoan, P., Pan, L., Pelkonen, VM. et al. The formation of protoplanetary disks through pre-main-sequence Bondi–Hoyle accretion. Nat Astron (2025). https://doi.org/10.1038/s41550-025-02529-3 https://doi.org/10.1038/s41550-025-02529-3
Contact Information: Paolo Padoan (ICREA-ICCUB), ppadoan@icc.ub.edu
