It’s a bird… it’s a plane… it’s a super star cluster! NASA’s Chandra X-ray telescope has imaged a star cluster that is “super” in every way. Westerlund 1 is super big, super massive, super young, super close – and it’s creating stars at a super fast rate.
Westerlund 1 is about 13,000 light-years away from Earth—which means it’s very close, relatively speaking—and the 3- to 5-million-year-old star cluster is about 7 light-years across. If that age doesn’t seem particularly young to you, remember that our middle-age solar system is about 4.6 BILLION years old. Westerlund 1 also has a mass equal to 100,000 suns, and is one of the few remaining super star clusters in the Milky Way.
Ultimately, the study of Westerlund 1 could help astronomers better understand the inner workings of these cosmic star factories. The image is part of the first data released by the Extended Westerlund Open Cluster Survey 1 and 2 (EWOCS), led by astronomers from the Italian National Institute of Astrophysics in Palermo. As part of the EWOCS program, Chandra observed Westerlund 1 for a total of about 12 days.
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At its current epoch, the Milky Way produces very few stars, with only a handful of stellar bodies formed each year. However, our galaxy was not always so peaceful. It once produced many more stars; at its peak about 10 billion years ago, it was born from tens to hundreds of stars each year.
Astronomers believe that this intense star formation is mostly localized to super star clusters like Westerlund 1. These are young star clusters with masses at least 10,000 times that of the Sun.
The X-rays from Westerlund 1, seen by Chandra and visible in the image as pink and white, are from young stars. Meanwhile, the pink, green and blue spots represent hot gas spread throughout the supercluster.
The new Chandra data have tripled the number of known X-ray sources in Westerlund 1. Before the EWOCS project, Chandra had detected 1,721 X-ray sources in the superstellar cluster; the EWOCS data, on the other hand, have detected almost 6,000 X-ray sources. These include faint stars less massive than the Sun.
This gives astronomers a new population of stars in Westerlund 1 to study. That is, not only does the proximity of Westerlund 1 make it a good target for probing star formation as a whole and decoding how such star accretion environments affect planet birth, but the super star cluster is also useful for examining how stars of different masses evolve.
Chandra also found that 1,075 of the stars it detected are clustered in a 4-light-year region at the heart of Westerlund 1. To imagine how dense this region is with stars, consider that there are 4.24 light-years between the sun and its neighbor its nearest star, Proxima Centauri.
The more diffuse pink dot that dominates the Chandra image of Westerlund 1 represents a halo of hot gas at the center of the super star cluster. Not only could this aspect of this region help give a more accurate estimate of the mass of Westerlund 1, but it could also help assess how this particular collection of stars formed and how it has changed over time.
The EWOCS results are discussed in a paper published in February in the journal Astronomy and Astrophysics.