ALMA Reveals New Insights into Planet Formation in Binary Systems

11 June, 2024 / Read time: 4 minutes

At the 244^th American Astronomical Society (AAS) meeting, researchers unveiled groundbreaking findings from a pioneering high-angular resolution program that sheds new light on planet formation in circumstellar disks around young stars in binary systems. Leveraging the unparalleled capabilities of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile and the Keck II 10-meter telescope in Hawaii, the study offers a transformative understanding of the conditions that nurture or inhibit planet formation.

Primordial disks of gas and dust around young stars are known to be the birthplaces of planets. However, the factors that ensure these disks last long enough for planet formation and what causes their early dissipation remain unclear. Circumstellar disks in pre-main sequence binary systems offer an ideal setting to investigate these questions. By examining disk properties, such as size, substructure, and inclination, in relation to stellar features like rotation speed and magnetic field strength, researchers are starting to unravel the complex interactions that shape these environments. Since binary and multiple-star systems are ubiquitous, studying them is particularly important.

This innovative research combines millimeter imaging of circumstellar disks with ALMA and high-resolution spectroscopy of young stars using Keck with the NIRSPEC spectrometer. By focusing on binaries with relatively well-determined orbits, the team can control for orbital parameters and highlight critical relationships between the properties of circumstellar disks and their host stars.

The study’s detailed examination of the D.F. Tau binary, quasi-twin stars with an average separation of 14 astronomical units (where 1 au equals the Earth-Sun distance) in an elongated orbit, reveals cool dust in two circumstellar disks detected by ALMA. One disk is magnetically locked to its central star and actively accreting material onto it. In contrast, the inner region of the other disk appears to have eroded and decoupled from its rapidly rotating central star, suggesting a potential link between stellar rotation, magnetic disk locking, and early disk dissipation. Misalignments between D.F. Tau’s orbit, circumstellar disks, and stellar inclinations may impact the disk evolution.

In contrast, another young star twin, F.O. Tau, a 22 au binary in a more circular orbit, displays ALMA-detected disks well-aligned with the binary orbit. Both components exhibit modest rotation speeds and appear magnetically locked to their disks. These observations reveal similar behavior in disks and stars, providing fresh insights into disk longevity and dissipation dynamics.

High-angular resolution observations from ALMA have shown intricate disk sub-structures, including spiral patterns, gaps, and ring formations around single stars and wide binary companions. Although disk substructures are unresolved in D.F. Tau and F.O. Tau, determining bulk disk properties in close binary systems significantly advances our understanding of planet formation environments.

Additional Information

Supported in part by NSF awards AST-1313399 and AST-2109179, this research reveals unique progress in astronomy. The insights gained not only enhance our comprehension of circumstellar disk dynamics but also pave the way for future discoveries in the mechanisms of planet formation.

This work was also supported by a NASA Keck PI Data Award, administered by the NASA Exoplanet Science Institute. Data presented herein were obtained at the W. M. Keck Observatory from telescope time allocated to the National Aeronautics and Space Administration through the agency’s scientific partnership with the California Institute of Technology and the University of California. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Indigenous Hawaiian community and declare themselves most fortunate to have the opportunity to conduct observations from this mountain.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

NRAO is a facility of the National Science Foundation, operated under a cooperative agreement by Associated Universities, Inc.

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