A study led by Paolo Padoan, ICREA research professor at the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and currently on leave at Dartmouth College (United States), is challenging the understanding of planetary disk formation around young stars. The paper, published in
Nature Astronomy, reveals that the environment plays a crucial role in determining the size and lifetime of these planetary disks, which are the sites of planet formation.
When a star forms, it is surrounded by a spinning disk of gas and dust. Over time, this material eventually forms the planets. Traditionally, scientists believed that once a disk forms, it simply loses too much over time as it feeds the star and the growing planets. However, Professor Paolo Padoan’s study introduces a new perspective that shows that young stars actually gain too much from their surroundings through a process known as Bondi-Hoyle accretion. This process helps to re-accrete the disk, making it larger and more durable than previously thought.
“Stars are born in groups or clusters within large gas clouds and can remain in this environment for several million years after their birth”, says Paolo Padoan, first author of the study.
“After a star forms, its gravity can capture more material from the parental gas cloud, which is not enough to change the star’s mass significantly but enough to restructure its disk. To understand what mass can attract a star with this Bondi-Hoyle accretion, and the spin and size of the disk induced by the new material, some fundamental properties of the chaotic motion of interstellar gas, known as
turbulence, would have to be modelled and understood”.
The study demonstrates that Bondi-Hoyle accretion can provide not only the mass but also the angular momentum needed to explain the observed sizes of protoplanetary disks. This revised understanding of disk formation and evolution resolves long-standing observational discrepancies and forces substantial revisions to current models of disk and planet formation.
Professor Padoan’s team used advanced computer simulations and analytical modelling to explain the size of the protoplanetary disks measured by ALMA, the world’s most powerful radio telescope. The combination of theoretical models and empirical data provided a solid framework for understanding the complex interactions between young stars and their environments.
“Comparing the observable data from the simulations with real observations is crucial to validate the simulations”, says ICUCB researcher and team member Veli-Matti Pelkonen. “However, simulations allow us to go beyond the observables to the underlying density, velocity and magnetic field structures, and to follow them in time. In this study, using simulation data, we were able to show that Bondi-Hoyle accretion plays an important role in late-stage star formation by increasing the lifetime and mass reservoir of protoplanetary disks”.
“With the increase of the computing power of supercomputers, we will be able to model even more complex physical processes in simulations, further increasing the fidelity of the simulations”, continues Pelkonen. “Combined with the new and powerful telescopes (such as the James Webb Space Telescope and ALMA, doing unparalleled observations of newly formed stars), these advances will continue to increase our understanding of star formation”.
The implications of this study extend beyond 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.