Stars are formed through the aggregation of gas in molecular clouds driven by gravity. As gas falls toward the star, it retains its angular momentum, creating a rotating disk known as a protoplanetary disk. The gas and dust in this rotating disk coagulate, eventually forming planets. According to this theory, not all of the gas that falls into the star is absorbed for star formation; rather, much of it is ejected as jets or outflows before returning to the surrounding star-forming environment.

By reanalyzing ALMA archival data of the young star WSB 52, which had previously been identified as having a protoplanetary disk, the research team unexpectedly discovered an explosively expanding bubble structure near the disk (Figure 1). Co-author Ryuta Orihara (the University of Tokyo, formerly a doctoral student at Ibaraki University) said, “ALMA’s high spectroscopic capabilities have unveiled the cross-section of an expanding bubble structure, as if it was examined with a CT scan.”

Further detailed analysis revealed a shock front created by the expanding bubble near the star (the right image of Figure 1), with the disk being distorted by the collision (the left image of Figure 2), and a fragment of gas in the disk blown away (the right image of Figure 2). Similar expanding bubble structures have been detected around other young stars through visible and near-infrared observations; however, none of them have indicated signs of collision between the bubble and the disk as observed this time. This phenomenon was also not predicted theoretically.

In addition, the research team found that the bubble’s center is aligned with the disk’s rotation axis through the analysis on the spatial relationship between the disk and the bubble. Based on this configuration, as well as the shape and energy of the bubble, the team concluded that a high-speed jet, emitted from WSB 52 hundreds of years ago, collided with cold material, causing the gas to compress and then the increased pressure from the compression caused the gas to explode, which resulted in the formation of the expanding bubble. The team also discovered that the explosion may have occurred closer to the central star since the bubble’s center exhibits motion away from the star. This suggests that the impact of the bubble collision immediately after its formation could have been far more intense than observed, indicating that the disk we see today is the result of having undergone such an impact.

Previously, stellar jets were thought to serve primarily as indirect suppliers of matter and energy for the surrounding environment. However, this research proved that star jets have a direct impact on the protoplanetary disk via the formation of bubble structures. Co-author Munetake Momose (Ibaraki University, with a cross-appointment at NAOJ from July 2025) said, “Stellar jets are a universal phenomenon observed in young stars, but this research has revealed a previously unknown role that they play.” If explosive bubble expansion like this one occurs universally around young stars, it may have had a major impact on the formation of various planetary systems, including our Solar System. Future in-depth study is expected to look further into the frequency of these explosions and their impact on disks.

Masataka Aizawa (Ibaraki University), who led this research, said, “We came upon this phenomenon by chance while reanalyzing ALMA archival data. In science fiction, there are scenes where a beam is fired at something to destroy it, causing an explosion with debris flying back at the shooter. Similar things occur in real astronomical phenomena, but with greater intensity. Through this discovery, I once again realized that nature is far more complex than humans think. In future research, I hope to further explore the effects of the explosions on the formation of stars and planetary systems.”

This research has been published in The Astrophysical Journal on 4th August 2025, as Masataka Aizawa et al. “Discovery of Jet-Bubble-Disk Interaction: Jet Feedback on a Protoplanetary Disk via an Expanding Bubble in WSB 52”.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).
ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

Figure 1. The left image shows 12CO (carbon monoxide) emission lines of WSB 52 at various wavelengths. The dashed line represents the expanding bubble model, and the red dot indicates the location of WSB 52. Panel 0 shows the zoom in continuum image of the protoplanetary disk. Panels 7 and 8 show the strong influence of a foreground molecular cloud. The right image is a cross-sectional diagram of the newly found phenomenon, showing the heights of the expansion bubbles that correspond to the number of each 12CO emission line image on the left. Credit: ALMA (ESO/NAOJ/NRAO), M. Aizawa et al.

Figure 2. The left image shows 12CO emissions from the protoplanetary disk of WSB 52. The distortion seen in the disk is thought to have been caused by collision with the bubble. The right image shows the high-velocity component in the disk that exceeds the escape velocity from the star’s gravity. Presumably, it indicates gas outflow from the disk. Credit: ALMA (ESO/NAOJ/NRAO), M. Aizawa et al.

[Movie]

A short animation conceptually showing the chain of events found through this research: A jet emitted by a baby star collides with a cloud of cold molecular gas, setting off the explosive expansion of a bubble.  The shock front created by the expanding bubble collides with the star’s disk and distorts it. Credit: ALMA (ESO/NAOJ/NRAO), M. Aizawa et al.