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News — Astronomers have unveiled an explosive cosmic fireworks display of stars interacting with their environment. This dazzling spectacle – due to powerful winds flowing from the stars – marks a major milestone in the ability to study the formation of the largest stars and to better understand how they affect their environments.

The researchers used NASA’s James Webb Space Telescope (JWST) to observe Westerlund 1, a so-called super star cluster with hundreds of very massive and potentially thousands of lower-mass young stars, with the Mid-Infrared Instrument (MIRI). Westerlund 1 is located across the Milky Way galaxy about 12,000 light-years from Earth.

The newly obtained JWST images of Westerlund 1 show many evolved, massive stars violently shedding their outer layers with bright patches throughout the image. These extended structures are known as ‘winds’ and show a surprising diversity in their shapes. The results provide details of the process where enormous amounts of energy from stellar winds and radiation are smashing into the local environment. This forms complex structures and stirs up the giant gas cloud, in which these stars are embedded in.

“We were really surprised to see all these different wind structures in Westerlund 1, as we expected most of the gas and dust to be blown away by the highly energetic radiation emitted by the massive stars”, says Kristina Monsch, an astronomer from the Center for Astrophysics | Harvard & Smithsonian who helped lead the research. “The fact that there is so much dust and gas in Westerlund 1 suggests that massive stars play an important role in shaping their environments, possibly even influencing the formation of stars, similar to our Sun.”

Westerlund 1 is one of the closest and most massive young star-forming clusters in our Galaxy, and it contains many rare supergiant and hypergiant stars, with masses ranging from eight to 100 times that of our Sun. Such stars live fast and die young with ages of only a few million years, which is in stark contrast to lower mass stars like our Sun that live for billions of years. Massive stars use up their hydrogen fuel much faster than lower mass stars, while at the same time losing most of their mass via winds and explosive outbursts from their outer layers, which JWST can observe at infrared wavelengths.

“Despite being rare star-forming environments in our Galaxy today, supermassive star clusters were very common in the early phases of the Universe,” describes Mario Guarcello of INAF - Astronomical Observatory of Palermo in Italy, who led the JWST observing campaign. “Westerlund 1 is therefore one of the best testbeds for extending our knowledge of the formation of stars, especially the most massive ones. The observations simply look like a cosmic fireworks display; the data is showing us that many stars and planets are born in incredibly explosive environments.”

Compared to the Sun, which will enter its red giant phase in five billion years or so, massive stars impact their local environments shortly after their formation, and eventually explode as energetic supernovae, leaving behind neutron stars or black holes. Only one supernova is expected to have gone off so far in Westerlund 1, however, more than 1,500 are expected over the next tens of million years.

“The discovery of these extended winds surrounding the massive stars in Westerlund 1 was only possible because we stared at the region for over six hours.”, says CfA astronomer Joshua Bennett Lovell who co-led the analysis of the JWST MIRI data. “But the time investment was worth the reward: we can now see a wide array of winds and ejecting material, vital clues to directly measure how young high-mass stars influence their surroundings.”

"We pushed our detection limit down to the smallest stars that can form," explained Juan Rafael Martínez-Galarza, also from the CfA, who supported the MIRI data analysis. "Thus, we will be able to determine the true content of the cluster and to measure properties such as the mass distribution of its stars, down to the regime of the least massive stars in the cluster." 

These results were presented today at the press conference of the annual winter meeting of the American Astronomical Society (AAS) in National Harbor, Maryland. A paper describing this work is being published in the Astronomy & Astrophysics journal and is available at [link]

The discoveries were made as part of the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, an international effort led by Mario G. Guarcello from the Palermo Astronomical Observatory (INAF) in Italy, aimed at studying the formation of stars and planets in the massive super star clusters Westerlund 1 and 2 using the James Webb Space Telescope and NASA’s Chandra X-ray Observatory. 

Kristina Monsch and Joshua Bennett Lovell from the Center of Astrophysics | Harvard & Smithsonian (CfA) led the JWST MIRI data calibration of Westerlund 1, which revealed the extended gas structures emanating from the most massive stars in the cluster. Juan Rafael Martinez-Galarza and Konstantina Anastasopoulou, both researchers at the CfA and Jeremy J. Drake (Lockheed Martin), also played important roles in the analysis of these extensive datasets.

About the CfA

The Center for Astrophysics | Harvard & Smithsonian is a collaboration between Harvard and the Smithsonian designed to ask—and ultimately answer—humanity's greatest unresolved questions about the nature of the universe. The Center for Astrophysics is headquartered in Cambridge, MA, with research facilities across the U.S. and around the world.