Westerlund 1 is the largest and closest ‘super’ star cluster to Earth. New data from NASA’s Chandra
These are the first data released publicly from a project called the Extended Westerlund 1 and 2 Open Clusters Survey, or EWOCS, led by astronomers at Italy’s National Institute of Astrophysics in Palermo. As part of EWOCS, Chandra Westerlund 1 observed for a total of about 12 days.
Currently, only a handful of stars form in our Milky Way each year, but in the past the situation was different. The Milky Way used to produce many more stars, probably reaching its peak of producing tens or hundreds of stars per year about 10 billion years ago, then gradually declining. Astronomers think that most of this star formation took place in massive star clusters known as ‘superstar clusters’, such as Westerlund 1. These are young star clusters containing more than 10,000 times the mass of the Sun. Westerlund 1 is between about 3 million and 5 million years old.
This new image shows the new deep Chandra data along with previously released data from NASA’s Hubble Space Telescope. The X-rays detected by Chandra show young stars (usually shown as white and pink) and diffusely heated gas throughout the cluster (colored pink, green and blue, in order of increasing temperature of the gas). Many of the stars picked up by Hubble appear as yellow and blue dots.
Only a few superstar clusters still exist in our Milky Way, but they provide important clues about this earlier era, when most of the stars in our Milky Way formed. Westerlund 1 is the largest of these remaining superstar clusters in the Milky Way, containing a mass of between 50,000 and 100,000 suns. It is also the closest super star cluster to Earth, about 13,000 light years away.
These properties make Westerlund 1 an excellent target for studying the impact of a superstar cluster’s environment on the formation process of stars and planets, as well as stellar evolution over a wide range of masses.
This new deep Chandra dataset from Westerlund 1 has more than tripled the number of known X-ray sources in the cluster. Before the EWOCS project, Chandra had detected 1,721 sources in Westerlund 1. The EWOCS data found nearly 6,000 X-ray sources, including fainter stars with lower mass than the Sun. This gives astronomers a new population to study.
One revelation is that 1,075 stars detected by Chandra are squeezed into the center of Westerlund 1, within four light-years of the cluster’s center. To get an idea of how crowded this is: four light-years is approximately the distance between the Sun and the nearest star to Earth.
The diffuse emission seen in the EWOCS data represents the first detection of a halo of hot gas around the center of Westerlund 1, which astronomers say will be crucial in assessing the cluster’s formation and evolution, and in giving a more accurate estimate of its mass.
An article published in the journal Astronomy and Astrophysics, led by Mario Guarcello of the Italian National Institute of Astrophysics in Palermo, discusses the research 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 monitors science from Cambridge Massachusetts and flight operations from Burlington, Massachusetts.
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This is an image of the star cluster Westerlund 1 and the surrounding area, as detected in X-ray and optical light. The black canvas of the room is peppered with colored points of light of various sizes, usually in red, green, blue and white.
At the center of the image is a semi-transparent, red and yellow gas cloud surrounding a group of tightly packed gold stars. The shape and distribution of the stars in the cluster are reminiscent of fizzing soda bubbles dancing above the ice cubes of a recently poured drink.
Megan Watzke
Chandra X-ray Center
Cambridge, Mass.
617-496-7998
Jonathan Deal
Marshall Space Flight Center
Huntsville, Ala.
256-544-0034