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Paris, France (ESA) Mar 08, 2010 Located half a billion light-years from Earth, ESO 306-17, is a large, bright elliptical galaxy in the southern sky of a type known as a fossil group. Astronomers use this term to emphasise the isolated nature of these galaxies. However, are they like fossils - the last remnants of a once active community - or is it more sinister than that? Did ESO 306-17 gobble up its next-door neighbours? Gravity brings galaxies together and bigger ones swallow smaller ones. There is evidence that our own Milky Way galaxy has "snacked" on numerous smaller galaxies that strayed too close. ESO 306-17 and other fossil groups may be the most extreme examples of galaxy cannibalism, ravenous systems that don't stop until they've devoured all of their neighbours. In this image, taken by the Advanced Camera for Surveys aboard Hubble in November 2008, it appears that ESO 306-17 is surrounded by other galaxies, but the bright galaxies at bottom left are thought to be in the foreground, not at the same distance in the sky. In reality, ESO 306-17 lies fairly abandoned in an enormous sea of dark matter and hot gas. When zooming in closely on ESO 306-17, one can see faint clusters of stars through the bright shine of the galaxy's large halo. These are globular clusters - tightly bound groups of stars that can often fend off cannibalism from larger, "bully" galaxies. Studying these surrounding clusters will prove helpful to astronomers in their pursuit to put the pieces of ESO 306-17's history together. Researchers are also using this image to search for nearby ultra-compact dwarf galaxies. Ultra-compact dwarfs are mini versions of dwarf galaxies that have been left with only their core due to interaction with larger, more powerful galaxies. Most ultra-compact dwarfs discovered to date are located near giant elliptical galaxies in large clusters of galaxies, so it will be interesting to see if researchers find similar objects in fossil groups.
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Related Links ESA/Hubble Information Centre Stellar Chemistry, The Universe And All Within It
First Of Missing Primitive Stars DiscoveredBoston MA (SPX) Mar 05, 2010 Astronomers have discovered a relic from the early universe - a star that may have been among the second generation of stars to form after the Big Bang. Located in the dwarf galaxy Sculptor some 290,000 light-years away, the star has a remarkably similar chemical make-up to the Milky Way's oldest stars. Its presence supports the theory that our galaxy underwent a "cannibal" phase, growing ... read more |
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