Westerlund 1 is the largest and closest “super” star cluster to Earth. New data from NASA’s Chandra X-ray Observatory, combined with other NASA telescopes, are helping astronomers peer deeper into this galactic factory of intense star production.
These are the first data published by a project called the Extended Westerlund 1 and 2 Open Clusters Survey, or EWOCS, led by astronomers at the Italian National Institute of Astrophysics in Palermo. As part of EWOCS, Chandra observed Westerlund 1 for a total of about 12 days.
Currently, only a handful of stars are formed in our galaxy each year, but in the past the situation was different. The Milky Way used to produce many more stars, probably reaching its peak of churning out tens or hundreds of stars a year about 10 billion years ago and gradually declining since then. Astronomers believe that most of this star formation took place in massive clusters of stars known as “superclusters,” such as Westerlund 1. These are young clusters of stars that contain more than 10,000 times the mass of the Sun. Westerlund 1 is about 3 to 5 million years old.
This new image shows new deep Chandra data along with previously released data from NASA’s Hubble Space Telescope. X-rays detected by Chandra show young stars (mostly represented as white and pink) as well as diffusely heated gas throughout the cluster (colored pink, green, and blue, in order of increasing gas temperature). Many stars captured by Hubble appear as yellow and blue dots.
Only a few superstar clusters still exist in our galaxy, but they offer an important clue about this earlier period when most of the stars in our galaxy formed. Westerlund 1 is the largest of these remaining superstars in the Milky Way, containing between 50,000 and 100,000 solar masses. It is also the closest supercluster to Earth at a distance of about 13,000 light years.
These properties make Westerlund 1 an excellent target for studying the influence of the supercluster environment on the process of star and planet formation, as well as on the evolution of stars over a wide range of masses.
This new deep Chandra dataset from Westerlund 1 more than triples the number of X-ray sources known in the cluster. Before the EWOCS project, Chandra detected 1,721 sources in Westerlund 1. The EWOCS data found nearly 6,000 X-ray sources, including fainter stars with less mass than the Sun. This gives astronomers a new population to study.
One revelation is that the 1,075 stars detected by Chandra are squeezed into the center of Westerlund 1 within four light-years of the cluster’s center. To give you an idea of ​​how crowded it is, four light years is about the distance between the Sun and the next closest star to Earth.
The diffuse emission seen in the EWOCS data represents the first detection of a halo of hot gas surrounding the center of Westerlund 1, which astronomers believe will be crucial for assessing the cluster’s formation and evolution and for more precisely estimating its mass.
A paper published in the journal Astronomy and Astrophysics, led by Mario Guarcello of the Italian National Institute of Astrophysics in Palermo, discusses the survey and the first results. Follow-up articles will discuss more about the results, including detailed studies of the brightest X-ray sources. This future work will analyze other EWOCS observations involving NASA’s James Webb Space Telescope and NICER (Neutron Star Interior Composition Explorer).
NASA’s Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center manages science from Cambridge Massachusetts and flight operations from Burlington, Massachusetts.
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This is an image of the Westerlund 1 cluster and the surrounding region as detected in X-ray and optical light. The black canvas of the space is dotted with colored dots of light of various sizes, mostly in shades of red, green, blue and white.
In the center of the image is a semi-transparent reddish-yellow cloud of gas surrounding a cluster of closely packed golden stars. The shape and distribution of the stars in the cluster resemble fizzy soda bubbles dancing over the ice cubes of a recently poured drink.
Megan Watzke
Chandra X-ray Centre
Cambridge, Mass.
617-496-7998
Jonathan Deal
Marshall Space Flight Center
Huntsville, Ala.
256-544-0034