Astronomers capture winding motion of circumstellar disc

Astronomers have directly captured the winding motion of spiral structures in a planet-forming disc for the first time. These spirals have been observed dynamically twisting around the young star IM Lupi, providing a window into the earliest stages of the formation of a planetary system. Stars form from dense clouds of gas and dust in stellar nurseries, that feed on the surrounding material under the influence of gravity, increasing in temperature and pressure till the conditions can sustain the fusion of hydrogen into helium. The remaining planets are formed in the leftover debris surrounding the newborn star, which is flattened into a disc because of a slight initial motion. 

Astronomers know of over 6,000 exoplanets so far, but the exact process by which these worlds are formed are not entirely clear. Planets are believed to be assembled in the protoplanetary discs surrounding newborn stars. The spiral structures in these discs are believed to play an important role in the process of planet formation, with planets emerging as solid particles accumulate within the spiral arms, or the spirals themselves fragmenting into individual worlds. Astronomers so far did not understand whether a spiral was a precursor to planet formation, or the product of a planet taking shape. 

Theoretical predictions indicated that spirals formed by the gravity of the disk should eventually wind up and disappear. Spirals created by the gravity of planets remain stable, and rotate with the planet. At least in the IM Lupi system, the observations revealed that the gravity of the disk itself creates the spirals. The astronomers were able to create a video spanning seven years showing the dynamic winding motion, with a speed matching theoretical models of spirals driven by disks. This is the first time that astronomers have detected the winding motion of spirals in circummstellar disks. A paper describing the research has been published in Nature Astronomy.