[Kyushu University] Planetary systems like our solar system are born within a disk of gas and dust (protoplanetary disk) surrounding a newly formed star. Observations with the ALMA telescope have revealed numerous patterns of alternating bright rings and dark grooves in these disks.
However, the mechanism by which these patterns are created remains unknown. Assuming that each groove was carved by a planet often leads to inconsistencies in terms of the time it takes for planets to form and the stability of their orbits. Therefore, an alternative mechanism that does not rely on planets has been sought.
In this study, we focused on the disk of the young star V1094 Sco, located about 500 light-years away in the direction of the constellation Lupus. We showed that the origin of the rings differs depending on the location.
The inner double groove can be naturally explained by assuming the presence of a single planet with a mass tens of times that of Earth. On the other hand, we showed that the regularly arranged rings on the outside can be explained by a mechanism called “secular gravitational instability,” where dust accumulates due to its own gravity.
Project Assistant Professor Masayuki Yamaguchi (also Project Assistant Professor at the National Astronomical Observatory of Japan) and Professor Masahiro Machida of the Faculty of Science, Kyushu University, collaborated with researchers from Japan and abroad to examine this disk in detail.
They integrated publicly available data from the ALMA telescope and applied PRIISM, a super-resolution technology developed in Japan. As a result, they resolved the quadruple rings and grooves in the range of 100 to 230 astronomical units (*5) from the central star with the clearest resolution to date. This disk is larger than any disk studied in nearby star-forming regions. The dust disk extends to about 13 times the distance between the Sun and Neptune, and the gas disk extends to about 25 times that distance.
Furthermore, they compared it with near-infrared images of the disk’s surface. They found that the inner double grooves were in the same position as the surface grooves. On the other hand, the outer rings did not have a corresponding structure on the surface. This difference was the key to indicating that different mechanisms are at work in the inner and outer regions.
The mechanism by which dust aggregates under its own gravity has been theoretically predicted, primarily by Japanese researchers. However, there have been very few examples of quantitative observations investigating whether this condition is met in actual disks. This study demonstrates that even in the distant, cold regions outside the solar system, dust can spontaneously aggregate and prepare the material for planets.
In the future, direct observations of planets believed to be hidden within this disk, as well as similar analyses of other disks, are expected to progress. This is expected to deepen our understanding of where and how planets are born.
A Hybrid Origin for the Multiple Ring-gap Structures in the Large Protoplanetary Disk V1094 Sco: A Low-mass Planet and Secular Gravitational Instability, The Astrophysical Journal (open access)
Astrobiology, exoplanet,
