The environment in which planets are born can be much more chaotic than previously thought. This is shown by a new image of the very young star RU Lupi, taken with the Atacama Large Millimeter/submillimeter Array.

Planets form in the disks of gas and dust around young stars. Many of these so-called protoplanetary disks therefore show empty zones, indicating that planets-in-the-making are in the process of swiping disk material. This creates an ordered system of concentric rings of dust around the young star, which is the basic material for the formation of the solid nuclei of planets. In addition, a protoplanetary disk contains much larger amounts of gas, which eventually ends up in the atmospheres of the formed planets.

The new ALMA recording shows that this gas does not have to be distributed nearly as neatly as the dust. Around RU Lupi scientists found an erratic spiral structure of gas that extends up to 150 billion kilometers from the star. (By comparison, the compact dust disk in the center has a radius of about nine billion kilometers.)

This discovery suggests that current ideas about the formation of planets are too simplistic. It seems that this process is much more chaotic than the well-known images of the central dust discs around stars suggest.

How the spiral structure around RU Lupi originated is still unclear. It is possible that the gas disk has so much mass that it collapses under the influence of its own gravity. It is also conceivable that the spiral structure is caused by the gravitational influence of another star, and another possibility is that the gas disk interacts with its environment, and interstellar gas accumulates along the spiral arms.