The text and images in this article were originally published on April 23, 2015 and reflect information about Westerlund 2 available at that time.
NASA Unveils Celestial Fireworks as Official Hubble 25th Anniversary Image
The brilliant tapestry of young stars flaring to life resemble a glittering fireworks display in the 25th anniversary NASA Hubble Space Telescope image released to commemorate a quarter century of exploring the solar system and beyond since its launch on April 24, 1990.
“Hubble has completely transformed our view of the universe, revealing the true beauty and richness of the cosmos,” said John Grunsfeld, astronaut and associate administrator of NASA’s Science Mission Directorate. “This vista of starry fireworks and glowing gas is a fitting image for our celebration of 25 years of amazing Hubble science.”
The sparkling centerpiece of Hubble’s silver anniversary fireworks is a giant cluster of about 3,000 stars called Westerlund 2, named for Swedish astronomer Bengt Westerlund, who discovered the grouping in the 1960s. The cluster resides in a raucous stellar breeding ground known as Gum 29, located 20,000 light-years away from Earth in the constellation Carina.
To capture this image, Hubble’s near-infrared Wide Field Camera 3 pierced through the dusty veil shrouding the stellar nursery, giving astronomers a clear view of the nebula and the dense concentration of stars in the central cluster. The cluster measures between 6 to 13 light-years across.
The giant star cluster is only about 2 million years old and contains some of our galaxy’s hottest, brightest, and most massive stars. Some of its heftiest stars unleash torrents of ultraviolet light and hurricane-force winds of charged particles that etch at the enveloping hydrogen gas cloud.
The nebula reveals a fantasy landscape of pillars, ridges, and valleys. The pillars, composed of dense gas and thought to be incubators for new stars, are a few light-years tall and point to the central star cluster. Other dense regions surround the pillars, including reddish-brown filaments of gas and dust.
The brilliant stars sculpt the gaseous terrain of the nebula and help create a successive generation of baby stars. When the stellar winds hit dense walls of gas, the shockwaves may spark a new torrent of star birth along the wall of the cavity. The red dots scattered throughout the landscape are a rich population of newly forming stars still wrapped in their gas-and-dust cocoons. These tiny, faint stars are between 1 million and 2 million years old—relatively young stars—that have not yet ignited the hydrogen in their cores. The brilliant blue stars seen throughout the image are mostly foreground stars.
Because the cluster is very young—in astronomical terms—it has not had time to disperse its stars deep into interstellar space, providing astronomers with an opportunity to gather information on how the cluster formed by studying it within its star-birthing environment.
The image’s central region, which contains the star cluster, blends visible-light data taken by Hubble’s Advanced Camera for Surveys with near-infrared exposures taken by the Wide Field Camera 3. The surrounding region is composed of visible-light observations taken by the Advanced Camera for Surveys. Shades of red represent hydrogen and bluish-green hues are predominantly oxygen.
The original observations of Westerlund 2 were obtained by the science team: Antonella Nota (ESA/STScI), Elena Sabbi and Carol Christian (STScI), Eva Grebel and Peter Zeidler (Astronomisches Rechen-Institut Heidelberg), Monica Tosi (INAF, Osservatorio Astronomico di Bologna), Alceste Bonanos (National Observatory of Athens, Astronomical Institute), and Selma de Mink (University of Amsterdam). Follow-up observations were made by the Hubble Heritage team: Zolt Levay (STScI), Max Mutchler, Jennifer Mack, Lisa Frattare, Shelly Meyett, Mario Livio, Carol Christian (STScI/AURA), and Keith Noll (NASA/GSFC).
Featured Image Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team
Fast Facts about Westerlund 2
About this Object
| Object Name: | Westerlund 2 and Gum 29 |
| Object Description: | Cluster and Emission Nebula/Star-forming Region |
| Position (J2000): | R.A. 10h 23m 58.10s Dec. –57° 45′ 48.96″ |
| Constellation: | Carina |
| Distance: | 20,000 light-years (6,130 parsecs) |
| Dimensions: | This image is 7.4 arcminutes (43.2 light-years or 13.4 parsecs) wide. |
About the Data
| Data Description: | Data of Westerlund 2 were obtained from the HST proposals 13038: A. Nota (ESA/STScI), E. Sabbi and C. Christian (STScI), E. Grebel and P. Zeidler (Astronomisches Rechen-Institut Heidelberg), M. Tosi (INAF, Osservatorio Astronomico di Bologna), A. Bonanos (National Observatory of Athens, Astronomical Institute), and S. de Mink (University of Amsterdam); and 14039: Z. Levay, M. Mutchler, J. Mack, L. Frattare, S. Meyett, M. Livio, and C. Christian (STScI/AURA), K. Noll (NASA/GSFC), A. Nota (STScI/ESA), and E. Sabbi (STScI). |
| Instrument | Filter | Exposure Date | Exposure Time |
| ACS/WFC | F555W (V) | September 2013–November 2014 | 9531 seconds |
| ACS/WFC | F814W (I) | September 2013–November 2014 | 9755 seconds |
| WFC3/IR | F125W (J) | November 2014 | 3788 seconds |
About this Image
| Image Credit: | NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team |
| Release Date: | April 23, 2015 |
| Colors | These images are composites of separate exposures acquired by the ACS and the WFC3 instruments on the Hubble Space Telescope. Several filters were used to sample broad and narrow wavelength ranges. The color results from assigning different hues (colors) to each monochromatic (grayscale) image associated with an individual filter. |
Additional Images of Westerlund 2
ACS/WFC F555W 
ACS/WFC F814W 
WFC3 F125W 
Scaled Image
A Scaled Image with Westerlund 2
| Stars form from gas and dust in vast clouds in spiral galaxies. We see these star-forming regions relatively nearby in our own Milky Way, and in distant galaxies, so their apparent size varies tremendously, but their true size varies as well, depending on the mass of material and other physical properties. This graphic compares four prominent star-forming regions at the same spatial scale, that is, as we would see them if they were all at the same distance. The Tarantula Nebula (30 Doradus) in our galactic neighbor, the Large Magellanic Cloud, is one of the largest star-forming regions known, much larger than any in the Milky Way, such as the relatively nearby Orion Nebula, more distant Carina Nebula, or Gum 29 (Westerlund 2). Star-forming Region Size Comparison courtesy of Z. Levay (STScI) |
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