The protoplanetary disk observed by Alma (left) and the protoplanetary disk during planetary migration simulated by aterui II (right). The dotted line in the simulation represents the orbit of the planet, and the gray area represents the area that does not belong to the simulation calculation domain. Source: Kazuhiro Kanagawa, Alma (ESO / NAOJ / NRAO)

Forming planets may explain the rings and gaps observed in the gas and dust disks around young stars. But this theory is difficult to explain why planets related to halos are rarely found. New supercomputer simulations show that after forming a ring, the planet can leave and leave the ring. This not only supports the theory of planetary ring formation, but also shows that a migrating planet can produce various patterns that match the observed disk planets. The related research was published in the Journal of astrophysics on November 12.

Young stars are surrounded by a protoplanetary disk of gas and dust. Atacama large millimeter / submillimeter array (ALMA) is one of the most powerful radio telescope arrays in the world. It has observed various dense or small rings and gaps in these protoplanetary disks. The gravitational effect of planets in the disk is a theory to explain these structures, but subsequent observation to find planets near the ring is largely unsuccessful.

In this study, teams from Ibaraki University and Tohoku University in Japan used the astronomical supercomputer aterui II of the National Astronomical Observatory of Japan to simulate a planet leaving its initial formation site. Their results show that in a low viscosity disk, the ring formed in the initial position of the planet will not move with the inward migration of the planet. The team identified three different phases. In the first stage, when the planet moves inward, the original halo is still intact. In the second stage, the initial ring begins to deform and the second ring begins to form in the new position of the planet. In the third stage, the initial ring disappears, leaving only the latter ring.

The three stages of ring formation and deformation simulated by aterui II (upper) are compared with the real examples observed by Alma (lower). The dotted line in the simulation indicates the orbit of the planet, and the gray area indicates the area that does not belong to the simulation calculation domain. In the above figure, the simulated protoplanetary disk is shown from left to right at the beginning of planetary migration (phase I), during planetary migration (phase II) and at the end of planetary migration (phase III).

These results help to explain why planets are rarely observed near the outer ring. The three stages determined in the simulation are very consistent with the patterns observed in the actual ring. High resolution observations from the next generation of telescopes will help determine how well these simulations match reality, and these telescopes will be able to better search for planets close to the central star.