Astronomers Unveil the Largest Known Bubble Around a Red Supergiant Star in the Milky Way
In a stunning discovery that reshapes our understanding of massive stellar evolution, astronomers from Chalmers University of Technology in Sweden have identified an enormous and expanding bubble of gas and dust enveloping a red supergiant star named DFK 52. This colossal structure is now recognized as the largest of its kind ever observed within our own Milky Way galaxy. Using highly sensitive radio observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, the team has mapped a vast, complex shell of material ejected by the star approximately 4,000 years ago—a mere blink in cosmic time.
DFK 52 is a red supergiant, a stellar behemoth in its terminal phase of life, bearing similarities to the famed star Betelgeuse. These stars are massive—often exceeding eight times the mass of our Sun—and are destined to end their existence in spectacular supernova explosions. However, this star presents a puzzling anomaly: it has undergone a violent mass-ejection event that produced an immense gaseous bubble without detonating as a supernova. The origin of this eruption remains enigmatic, challenging current astrophysical models of how such massive stars lose mass in their final millennia.
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The bubble surrounding DFK 52 stretches an astonishing 1.4 light years across, making it thousands of times larger than the entire Solar System. If this star were as close to Earth as Betelgeuse, the bubble would cover roughly one-third of the full Moon’s apparent diameter in the night sky. The extraordinary scale and complexity of this structure were revealed through ALMA’s capability to detect millimeter-wavelength emissions, specifically targeting molecular species like carbon monoxide (CO) and silicon monoxide (SiO), which trace the cold, dense gas expelled by the star.
ALMA’s observations further allowed the research team to apply Doppler velocity measurements, deciphering how parts of the bubble are moving relative to us. The red-shifted regions indicate segments of the bubble moving away, while blue-shifted regions represent material moving toward us along our line of sight. This Doppler mapping crucially confirmed that the structure is not static but is expanding outward—evidence of a dynamic evolutionary phase in the life of this massive star.
Lead astronomer Mark Siebert expressed his astonishment at the findings. He remarked, “We were surprised to see that DFK 52 is surrounded by such a messy, gargantuan bubble of gas and dust. It is essentially a twin of Betelgeuse in terms of stellar characteristics, yet its environment betrays a turbulent recent history we did not expect.” This chaotic bubble, rich with molecules that once composed part of the star’s outer layers, signals a highly energetic eruption event whose mechanisms and triggers are still under investigation.
The event that generated this bubble likely involved a rapid expulsion of stellar material, ejecting an amount comparable in mass to our Sun in just a few thousand years. Such a forceful shedding dramatically alters the star’s immediate environment, redistributing heavy elements and affecting future star formation processes by enriching the interstellar medium. Moreover, the existence of this bubble opens compelling questions about the survival and stability of such stars after such catastrophic mass-loss episodes.
One intriguing hypothesis to explain these phenomena involves the presence of a hidden binary companion. Companion stars can exert significant gravitational effects, potentially inducing or enhancing mass-loss events in their partners. “The presence of a yet-undetected companion could have played a critical role in catalyzing this violent ejection, much like conjectured for Betelgeuse itself,” Siebert noted. Future targeted observations aim to investigate this possibility.
Red supergiants like DFK 52 represent a fleeting but critical stage in the life cycle of the Universe’s most massive stars. These celestial giants are laboratories for studying nucleosynthesis—the process through which new heavy elements forge inside stars and are later disseminated into space. The elements propagated by such stars eventually become the building blocks for new stars, planets, and, ultimately, life as we know it. Understanding the mass-loss history and final fate of red supergiants helps refine supernova progenitor models critical to astrophysics.
Elvire De Beck, co-investigator on the project, emphasized the broader significance of this discovery: “The bubble’s size and mass hint at highly energetic processes shaping stellar death throes, but exactly how these explosive ejections fit into the supernova timeline remains a profound mystery.” Further monitoring of DFK 52 is planned to observe its ongoing evolution and to determine whether it might be a precursor to one of the galaxy’s next stellar explosions.
Among the community of astrophysicists, this discovery invites fresh theoretical explorations into the late-stage behavior of massive stars, potentially revising existing models of stellar wind interactions, eruption mechanisms, and supernova outburst triggers. The resolving power and sensitivity of ALMA have once again demonstrated its pivotal role in unveiling the hidden details of our cosmic neighborhood, providing unprecedented insight into phenomena that optical telescopes cannot capture.
In sum, the discovery of this expansive, accelerating bubble around DFK 52 is a landmark in Galactic astronomy. Not only does it expand our inventory of known massive stellar ejecta, but it also provides a natural laboratory to examine the physics that dictate the life cycles of the Universe’s giants. By piecing together the sequence of events leading up to supernova explosions, astronomers hope to better predict and understand these cosmic fireworks that dramatically influence galaxy evolution.
This monumental finding also underscores the collaborative nature of modern astronomy, integrating observational expertise from Swedish institutions such as the Onsala Space Observatory and international partners operating one of the world’s premier radio observatories. As data continue to pour in, the structure and dynamics of DFK 52’s bubble offer fertile ground for discovery, promising to deepen humanity’s grasp of the turbulent, transformative final acts of stellar existences.
Subject of Research: Red supergiant star DFK 52 and the large gaseous bubble surrounding it, formed by a past eruption event.
Article Title: Stephenson 2 DFK 52: Discovery of an exotic red supergiant in the massive stellar cluster RSGC2
News Publication Date: 6-Aug-2025
Web References:
ALMA telescope: https://www.eso.org/public/teles-instr/alma
Research Paper DOI: http://dx.doi.org/10.1051/0004-6361/202555975
ESO Picture of the Week: https://www.eso.org/public/images/potw2531a
References:
Siebert, M., De Beck, E., Vlemmings, W., & Quintana Lacaci, G. (2025). Stephenson 2 DFK 52: Discovery of an exotic red supergiant in the massive stellar cluster RSGC2. Astronomy and Astrophysics. DOI: 10.1051/0004-6361/202555975
Image Credits: ALMA (ESO/NAOJ/NRAO)/M. Siebert et al
Keywords
Red Supergiant, DFK 52, ALMA, Stellar Evolution, Stellar Eruption, Gas and Dust Bubble, Supernova Progenitor, Doppler Measurements, Molecular Cloud, Stellar Mass Loss, Milky Way, Radio Astronomy
Tags: astrophysical models of massive starsAtacama Large Millimeter Array observationsBetelgeuse comparison in astronomyChalmers University of Technology researchcosmic time scales in astronomygas and dust structures in spacelargest bubble in Milky Waymass-ejection events in starsmysteries of stellar life cyclesred supergiant star DFK 52stellar evolution discoveriessupernova explosion anomalies
