Tour: 'Super' Star Cluster Shines in New Look From NASA's Chandra

Westerlund 1 is the biggest and closest “super” star cluster to Earth. New data from NASA’s Chandra X-ray Observatory, in combination with other NASA telescopes, is helping astronomers delve deeper into this galactic factory where stars are vigorously being produced. These are the first data to be publicly released from a project called the Extended Westerlund 1 and 2 Open Clusters Survey, or EWOCS.

Currently, only a handful of stars form in our galaxy each year, but in the past the situation was different. The Milky Way used to produce many more stars, likely hitting its peak of churning out dozens or hundreds of stars per year about 10 billion years ago and then gradually declining ever since. Astronomers think that most of this star formation took place in young massive clusters of stars, known as “super star clusters,” like Westerlund 1. These are young clusters of stars that contain more than 10,000 times the mass of the sun.

Only a few super star clusters still exist in our galaxy, but they offer important clues about this earlier era when most of our galaxy’s stars formed. Westerlund 1 is the biggest of these remaining super star clusters in the Milky Way and contains a mass between 50,000 and 100,000 suns. It is also the closest super star cluster to Earth at about 13,000 light-years.

These qualities make Westerlund 1 an excellent target for studying the impact of a super star cluster’s environment on the formation process of stars and planets as well as the evolution of stars over a broad range of masses.

This new deep Chandra dataset of Westerlund 1 has more than tripled the number of X-ray sources known in the cluster. Before the EWOCS project, Chandra had detected 1,721 sources in Westerlund 1. The EWOCS data found almost 6,000 X-ray sources, including fainter stars with lower masses than the Sun. This gives astronomers a new population to study and learn from.