Science
May 29, 2026

Simulations Explain Baby Carriage Wheels Around Baby Stars

Left: Observations of a star-forming region with a hub-and-spoke shape like a baby carriage wheel. Right: A similar shape produced by a simulation using the ATERUI III supercomputer. (Credit: M. S. N. Kumar, ESA/Herschel, NASA/JPL-Caltech (Spitzer), S. Nozaki, S. Inutsuka) Image (716KB)

Research using multiple supercomputers, including ATERUI III at the National Astronomical Observatory of Japan, has found a possible explanation for the hub-and-spoke pattern seen in some molecular clouds where baby stars are forming. According to the new numerical simulations, if an external shock interacts with magnetic fields which have been warped by the motion of the clouds, gas can be channeled into a shape resembling the spokes on the wheels of a baby carriage.

When parts of molecular clouds become dense enough, they can collapse under self-gravity. As a result of this collapse, the gas in the clouds condenses into protostars which will grow into stars. For this reason, molecular clouds are nicknamed “stellar cradles.” But some of these sites of star formation are more like baby carriages than cradles because they have filaments of gas extending toward a central hub, forming a shape like a spoked wheel.

Researchers from Kyushu University and Nagoya University investigated the possibility that magnetic fields within the clouds might play a role in forming this distinct shape. Using ATERUI III, a dedicated-astronomy supercomputer operated by the National Astronomical Observatory of Japan, they modeled how gas and magnetic fields evolve together over time. The results show that as the cloud collapses under self-gravity, it pulls the magnetic field lines inward, bending them into an hourglass shape. The team then simulated the effects of a disturbance like a shock wave from a nearby supernova remnant or from expanding gas around a massive star. The team found that if this shock hits the curved magnetic field at certain angles, it strengthens parts of the magnetic field, forming invisible channels that guide compressed gas into long, narrow filaments converging toward the center.

The team now plans to conduct more simulations to test whether this mechanism can explain more asymmetric and complex shapes. This will help clarify how the diversity of observed hub-filament systems reflects differences in cloud environments and how such environments shape the formation of massive stars and clusters.

Numerical simulation of the formation of a hub–filament system molecular cloud. After an interstellar shock wave passes through a molecular cloud, multiple filaments characteristic of a hub–filament system develop radially toward the center. The left panels show the cloud viewed perpendicular to the propagation direction of the interstellar shock wave, while the right panels show the view parallel to the direction from which the shock wave approaches. The numbers in the upper left indicate the elapsed time since the start of the simulation. Note that the right panels are displayed using a different density range than the left panels in order to make the higher-density gas easier to distinguish. (Credit: Shingo Nozaki (Kyushu University))

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