February 1, 2023

Stellar “Ashfall” Could Help Distant Planets Grow – 3D Simulation Provides Insights on Protoplanetary Mystery

The dust particles swept up by the bipolar outflow from the center of the protoplanetary disk are stacked up on the external edge of the disk. The worlds very first 3D simulation simultaneously thinking about dust movement and growth in a disk around a young star has revealed that big dust from the main area can be entrained by and then ejected by gas outflows, and eventually fall back onto the external regions of the disk where it might enable planetesimal formation. (1 )The dust grows in the disk and moves to the center of the protoplanetary disk near the protostar. (4 )The dust that leaves the outflow falls on the external edge of the protoplanetary disk. The team discovered that big dust particles grown in the main area can be carried out perpendicular to the disk by streams of gas, called bipolar outflow, erupting out from the disk.

Artists impression of the “Ashfall” in a protoplanetary disk. The dust particles swept up by the bipolar outflow from the center of the protoplanetary disk are accumulated on the outer edge of the disk. Credit: Kagoshima University
The worlds very first 3D simulation at the same time considering dust movement and growth in a disk around a young star has actually revealed that big dust from the central region can be entrained by and then ejected by gas outflows, and ultimately fall back onto the external areas of the disk where it may make it possible for planetesimal formation. This process can be likened to volcanic “ashfall” where ash carried up by gas throughout an eruption falls back on the area around the volcano. These outcomes assist to describe observed dust structures around young protostars.
The circulations of gas (left panel) and dust (best panel). The orange and red lines indicate the gas and dust paths (streamlines), respectively, and the white arrows show the circulation instructions. The yellow area represents the protoplanetary disk formed in the simulation. Credit: Yusuke Tsukamoto
Observations by ALMA (Atacama Large Millimeter/submillimeter Array) have actually revealed gaps in protoplanetary disks of gas and dust around young stars. The gravitational results of planets are believed to be among the factors for the development of these rings. Some rings are seen even further out than the position of Neptune in the Solar System. At these ranges, dust, an important part to world formation, should be scarce. Furthermore, the dust is anticipated to move in towards the central region of the disk as it grows. So how planets can form in the external regions has been a secret.
Artists impression of the “Ashfall” in a protoplanetary disk. (1 )The dust grows in the disk and migrates to the center of the protoplanetary disk near the protostar. (2 )When the dust reaches the vicinity of the protostar, the dust particles are raised vertically by the gas outflow. (3 )Dust particles are separated from the outflow by centrifugal force. (4 )The dust that leaves the outflow falls on the external edge of the protoplanetary disk. Credit: Kagoshima University
A research group led by Yusuke Tsukamoto at Kagoshima University used ATERUI II, the worlds most powerful supercomputer devoted to astronomy calculations at the National Astronomical Observatory of Japan, to perform the worlds first 3D simulation of dust movement and development in a protoplanetary disk. The group found that large dust particles grown in the main area can be brought out perpendicular to the disk by streams of gas, called bipolar outflow, appearing out from the disk. This dust then wanders out from the outflow and gravity pulls it back down to the external part of the disk. Tsukamoto comments, “Living in Kagoshima, in the shadow of the active volcano Mt. Sakurajima, I naturally thought about volcanic ashfall when I saw the simulation results.”

The simulation shows that this “stellar ashfall” can enrich big dust in the outer area of the protoplanetary disk and facilitate planetesimal development, which may eventually trigger planet formation.
NAOJ supercomputer ATERUI II (Cray XC50). Credit: NAOJ
This research study utilized the NAOJ supercomputer ATERUI II (Cray XC50) for the simulations of protoplanetary disks. ATERUI II is operated at NAOJ Mizusawa Campus (Oshu, Iwate) with a theoretical peak efficiency of 3.087 Pflops.
Recommendation: “” Ashfall” caused by molecular outflow in protostar evolution” by Yusuke Tsukamoto, Masahiro N. Machida and Shu-ichiro Inutsuka, 15 October 2021, Astrophysical Journal Letters.DOI: 10.3847/ 2041-8213/ ac2b2f.

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