[NASA] NASA’s Fermi Spots Young Star Cluster Blowing Gamma-Ray Bubbles

[SpaceMan 0]

4 min read

NASA’s Fermi Spots Young Star Cluster Blowing Gamma-Ray Bubbles

For the first time, astronomers using NASA’s Fermi Gamma-ray Space Telescope have traced a budding outflow of gas from a cluster of young stars in our galaxy — insights that help us understand how the universe has evolved as NASA explores the secrets of the cosmos for the benefit of all.

The cluster, called

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, is located about 12,000 light-years away in the southern constellation Ara. It’s the closest, most massive, and most luminous super

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in the Milky Way. The only reason Westerlund 1 isn’t visible to the unaided eye is because it’s surrounded by thick clouds of dust. Its outflow extends below the plane of the galaxy and is filled with high-speed, hard-to-study particles called

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.

“Understanding cosmic ray outflows is crucial to better comprehending the long-term evolution of the Milky Way,” said Marianne Lemoine-Goumard, an astrophysicist at the

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in France. “We think these particles carry a large amount of the energy released within clusters. They could help drive galactic winds, regulate star formation, and distribute chemical elements within the galaxy.”

A

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detailing the results published Dec. 9 in Nature Communications. Lemoine-Goumard led the research with Lucia Härer and Lars Mohrmann, both at the

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in Heidelberg, Germany.

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This image of super star cluster Westerlund 1 was captured with the Near-InfraRed Camera on NASA’s James Webb’s Space Telescope. The cluster is largely hidden at visible wavelengths by dust clouds, which infrared light penetrates. Westerlund 1’s large, dense, and diverse stellar population of massive stars has no other known counterpart in the Milky Way.

ESA/Webb, NASA & CSA, M. Zamani (ESA/Webb), M. G. Guarcello (INAF-OAPA) and the EWOCS team

Download high-resolution images from NASA’s Scientific Visualization Studio

Super star clusters like Westerlund 1 contain more than 10,000 times our Sun’s mass. They are also more luminous and contain higher numbers of rare, massive stars than other clusters.

Scientists think that

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and stellar winds within star clusters push ambient gas outward, propelling cosmic rays to near light speed. About 90% of these particles are hydrogen nuclei, or protons, and the remainder are electrons and the nuclei of heavier elements.

Because cosmic ray particles are electrically charged, they change course when they encounter magnetic fields. This means scientists can’t trace them back to their sources. Gamma rays, however, travel in a straight line.

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are the highest-energy form of light, and cosmic rays produce gamma rays when they interact with matter in their environment.

Most gamma-ray observations of stellar clusters have limited resolution, so astronomers effectively see them as indistinct areas of emission. Because Westerlund 1 is so close and bright, however, it’s easier to study.

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Westerlund 1 is located closer to the center of the Milky Way than our Sun, as shown in this artist’s concept. Westerlund 1 is one of only a few known super star clusters in our galaxy and is the closest, brightest, and most massive one discovered so far.

NASA’s Goddard Space Flight Center/Conceptual Image Lab

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This artist’s concept shows the location of Westerlund 1 relative to our Sun as seen from the underside of our Milky Way galaxy. The magenta bubble illustrates what the nascent outflow might look like in gamma rays. Westerlund 1 is located slightly below the middle of the galactic disk, so stellar activity pushes gas preferentially along a path of lower density beneath the disk.

NASA’s Goddard Space Flight Center/Conceptual Image Lab

In

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, scientists using a group of telescopes in Namibia operated by the Max Planck Institute called the

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detected a distinct ring of gamma rays around Westerlund 1 with energies trillions of times higher than visible light.

Lemoine-Goumard, Härer, and Mohrmann wondered if the cluster’s unique properties might allow them to see other details by looking back through nearly two decades of

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data at slightly lower energies — millions to billions of times the energy of visible light.

Fermi’s sensitivity and resolution allowed the researchers to filter out other gamma-ray sources like rapidly spinning stellar remnants called pulsars, background radiation, and Westerlund 1 itself.

What was left was a bubble of gamma rays extending over 650 light-years from the cluster below the plane of the Milky Way. That means the outflow is about 200 times larger than Westerlund 1 itself.

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Data from NASA’s Fermi Gamma-ray Space Telescope reveal the budding gas bubble of star cluster Westerlund 1. Brighter colors indicate a stronger likelihood that gamma rays arise from specific types of point sources, notably two pulsars located at center and in the brightest portion of the image. Pink contours denote steep changes in likelihood. An underlying orange-magenta feature extends down the image, starting from the cluster’s location, and represents the nascent outflow. The grey lines indicate distance below the galactic plane. The bubble is over 650 light-years long and angles slightly away from us. Westerlund 1’s stellar activity more easily pushes gas outward into lower-density regions of the galaxy’s disk.

NASA’s Goddard Space Flight Center/Lemoine-Goumard et al. 2025; ESA/Webb, NASA & CSA, M. Zamani (ESA/Webb), M. G. Guarcello (INAF-OAPA) and the EWOCS team

The researchers call this a nascent, or early stage, outflow because it was likely recently produced by massive young stars within the cluster and hasn’t yet had time to break out of the galactic disk. Eventually it will stream into the galactic halo, the hot gas surrounding the Milky Way.

Westerlund 1 is located slightly below the galactic plane, so the researchers think the gas expanded asymmetrically, following the path of least resistance into a zone of lower density below the disk.

“One of the next steps is to model how the cosmic rays travel across this distance and how they create a changing gamma-ray energy spectrum,” Härer said. “We’d also like to look for similar features in other star clusters. We got very lucky with Westerlund 1, though, since it’s so massive, bright, and close. But now we know what to look for, and we might find something even more surprising.”

“Since it started operations 17 years ago, Fermi has continued to advance our understanding of the universe around us,” said Elizabeth Hays, Fermi’s project scientist at NASA’s

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in Greenbelt, Maryland. “From activity in distant galaxies to lightning storms in our own atmosphere, the gamma-ray sky continues to astound us.”

By Jeanette Kazmierczak
NASA’s

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, Greenbelt, Md.

Media Contact:
Claire Andreoli
301-286-1940
NASA’s Goddard Space Flight Center, Greenbelt, Md.

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Last Updated

Dec 18, 2025

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