Westerlund 1: A Stellar Laboratory Unveiled by Webb.

The open cluster Westerlund 1, featured as the Webb Picture of the Month, is located approximately 12,000 light-years away in the southern constellation Ara (the Altar). Discovered in 1961 by Swedish astronomer Bengt Westerlund, this cluster resides behind a vast interstellar cloud of gas and dust, making it a prime site for studying extreme stellar physics.

Westerlund 1 stands out for its dense population of massive stars, unparalleled in the Milky Way. It includes evolved stars across various classifications, such as Wolf-Rayet stars, OB supergiants, yellow hypergiants, and luminous blue variables. Astronomers estimate its age to be between 3.5 and 5 million years, marking it as a young cluster. Over time, it is expected to evolve into a globular cluster, a tightly packed assembly of older stars.

In the past, the Milky Way experienced a surge in star formation, peaking around 10 billion years ago. During this era, massive clusters like Westerlund 1 likely formed, harboring over 10,000 times the Sun’s mass in a small volume. Today, only a few super star clusters remain, making Westerlund 1 a crucial subject for understanding star formation processes.

The cluster is home to hundreds of massive stars, some nearly a million times brighter than the Sun. If our Solar System were at its center, our sky would be illuminated by hundreds of stars as bright as the full Moon. Estimated to contain 50,000 to 100,000 times the Sun’s mass within a region less than six light-years across, Westerlund 1 is the most massive compact young cluster identified in our galaxy.

The multitude of massive stars in Westerlund 1 suggests it will significantly influence its surroundings, with predictions of over 1,500 supernovae occurring within 40 million years. This unique cluster offers astronomers an exceptional opportunity to investigate the environmental impacts of super star clusters on star and planet formation.

Captured as part of The Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) using Webb’s Near-InfraRed Camera (NIRCam), these observations aim to reveal the population of low-mass stars and examine the environments surrounding the most massive stars. Webb’s capabilities enable detailed study of stellar feedback processes and their influence on star formation within the cluster’s parental clouds.

The stunning imagery reveals a vibrant cluster of bright stars, each displaying distinctive colors that reflect their types, surrounded by billowing patches of red gas, illuminated by stellar light. This research will enhance our understanding of stellar evolution and the dynamics within these extreme environments.