Queen Mary-led team discovers warped planetary nurseries

Visualisation of the warped disc around the young star MWC 758, with warping exaggerated by a factor four to make it visible. Both panels show properties of the disc inferred from CO emission. On the left-hand side, we see deviations in the line-of-sight velocity from the expected rotation if the disc were flat. The variations in velocity can be used to infer the warp structure. On the right-hand side we see variations in the gas temperature, from which we can see evidence of shadowing in areas of the disc. Credit: A. Winter

The textbook picture of how planets form – serene, flat discs of cosmic dust – has just received a significant cosmic twist. New research, published in the Astrophysical Journal Letters, is set to reshape this long-held view. An international team of scientists, wielding the formidable power of the Atacama Large Millimetre/submillimetre Array (ALMA), has found compelling evidence that many protoplanetary discs, the very birthplaces of planets, are in fact subtly warped.
 
These slight bends and twists in the disc plane, often just a few degrees, bear a striking resemblance to the subtle tilts observed among the planets in our own Solar System. This discovery suggests the initial conditions for planetary systems might be far less orderly than previously thought, with profound implications for how planets grow and settle into their final orbits.

Dr Andrew Winter, the lead author of the study from Queen Mary University of London where he is Royal Society University Research Fellow in astronomy, said: "Our results suggest that protoplanetary discs are slightly warped. This would be quite a change in how we understand these objects and has many consequences for how planets form. Particularly interesting is that the couple of degree warping is similar to the differences in inclination between our own Solar System planets."

To uncover these subtle twists, the team meticulously analysed Doppler shifts – tiny changes in the radio waves emitted by carbon monoxide (CO) molecules swirling within the discs. These shifts act like a cosmic speedometer, revealing the gas's exact motion. As part of a major ALMA programme called exoALMA, researchers used this flagship observatory to map the gas's velocity across each disc in unprecedented detail. By carefully modelling these intricate patterns, they were able to detect when different regions of a disc were slightly tilted, thus revealing the warps.

"These modest misalignments may be a common outcome of star and planet formation," Dr Winter added, noting the intriguing parallel with our own Solar System. The research not only provides a fresh perspective on the mechanics of planet formation but also raises new questions about why these discs are warped – a mystery the team is eager to unravel. 

Dr Myriam Benisty, director of the Planet and Star Formation Department at the Max Planck Institute for Astronomy said,“exoALMA has revealed large scale structures in the planet forming discs that were completely unexpected. The warp-like structures challenge the idea of orderly planet formation and pose a fascinating challenge for the future.”

Is it the gravitational pull of unseen companion stars, or perhaps the chaotic dance of gas and dust that twists these stellar cradles? The findings show that these subtle disc warps, often tilting by as little as half a degree to two degrees, can naturally explain many of the prominent large-scale patterns observed in the gas's motion across the discs. They even suggest these warps could be responsible for creating intriguing spiral patterns and slight temperature variations within these cosmic nurseries.

If these warps are a key driver of how gas moves within the disc, it profoundly changes our understanding of critical processes like turbulence and how material is exchanged – ultimately dictating how planets form and settle into their final orbits. Intriguingly, the nature of these warps appears to be connected to how much material the young star is actively drawing in towards its centre. This hints at a dynamic link between the disc's innermost regions, where the star is fed, and its outer, planet-forming areas. 

This discovery offers a thrilling glimpse into the complex and often surprising realities of planet formation, fundamentally changing our cosmic blueprint and opening new avenues for understanding the diverse worlds beyond our Sun.

This research was conducted by the ‘exoALMA’ collaboration that is an international collaboration of institutions including the Max-Planck Institute for Astronomy (MPIA), University of Florida, Leiden Observatory (Leiden University), European Southern Observatory, Università degli Studi di Milano, Massachusetts Institute of Technology, Center for Astrophysics | Harvard & Smithsonian, Univ. Grenoble Alpes, Universidad de Chile, University of St. Andrews, Université Côte d’Azur, The University of Georgia, Monash University, University of Leeds, National Astronomical Observatory of Japan, University of Cambridge, Ibaraki University, Academia Sinica Institute of Astronomy & Astrophysics, The Graduate University for Advanced Studies (SOKENDAI), Wesleyan University, and The Pennsylvania State University. 
 

Read the research.