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News Release 5 of 34

October 30, 2003 05:00 AM (EST)

News Release Number: STScI-2003-32

Megastar-Birth Cluster is Biggest, Brightest and Hottest Ever Seen

October 30, 2003: A mysterious arc of light found behind a distant cluster of galaxies has turned out to be the biggest, brightest, and hottest star-forming region ever seen in space. The so-called Lynx arc is 1 million times brighter than the well-known Orion Nebula, a nearby prototypical star-birth region visible with small telescopes. The newly identified super-cluster contains a million blue-white stars that are twice as hot as similar stars in our Milky Way galaxy. It is a rarely seen example of the early days of the universe where furious firestorms of star birth blazed across the skies. The spectacular cluster's opulence is dimmed when seen from Earth only because it is 12 billion light-years away.

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Q & A: Understanding the Discovery

  1. 1. If the star-birth cluster is so bright, why has it taken so long to find it?

  2. The super star-birth region is 12 billion light-years away. It is very faint as seen from Earth. Astronomers only came across the megacluster because its image was brightened and magnified as the light traveled toward Earth.

  3. 2. What magnified the image of the distant star-birth cluster?

  4. On its way to Earth the star-birth region's light passed near a foreground cluster of galaxies 5.4 billion light-years away. The gravity of the cluster bent and brightened the image, just like the lens in a magnifying glass does.

  5. 3. How much bigger is the star-birth cluster than those found elsewhere in the universe?

  6. There are no such regions in our Milky Way or in nearby observable galaxies. The largest known star-birth clusters in our galaxy are the Arches clusters in the galactic center, the Carina Nebula in the constellation Fornax, and the 30 Doradus cluster in the Large Magellanic Cloud. These clusters contain only hundreds or thousands of super-hot stars, so they are a fraction of the size of this megacluster.

  7. 4. How do we know the stars are so much hotter?

  8. Analysis of the color and of the intensity of light coming from the megacluster offers clues. The light started out as ultraviolet light from the hottest stars and was stretched to red light. The hotter a star is, the bluer it is, and the more massive it is. So, these are the most massive stars seen in the universe.

  9. 5. Why are the stars more massive than those in our galaxy?

  10. It was easier to make stars over 100 times the mass of our Sun in the early universe. These early generation stars were made almost purely of primordial hydrogen and helium. There were fewer heavier elements in the early universe because they had not been cooked up in stars. Heavier elements help cool a cloud to contract and form a star. A lot more gas was needed to build stars when there were fewer heavier elements. Many of the stars turned out to be hundreds of times as massive as our Sun.

  11. 6. Where is the megacluster today?

  12. The megacluster's stars would have exploded in a crescendo of about a million supernova explosions. The heavier elements created by these stars were blasted back into space. Some of this material may have formed second-generation stars. The megacluster's surviving stars may have coalesced with other clusters to form the earliest galaxies.

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Credit: ESA, NASA and Robert A.E. Fosbury (European Space Agency/ Space Telescope-European Coordinating Facility, Germany)