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Re: Yahoo! News Story - Oddball 'Blue Stragglers' Are Stellar Cannibals - Yahoo! News

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  • mahtezcatpoc
    ... http://news.yahoo.com/s/space/20090114/sc_space/oddballbluestragglersarestellarcannibals ... Oddball Blue Stragglers Are Stellar Cannibals Andrea
    Message 1 of 2 , Jan 14, 2009
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      Oddball 'Blue Stragglers' Are Stellar Cannibals



      Andrea Thompson
      Senior Writer
      SPACE.com – Wed Jan 14, 1:19 pm ET

      Astronomers have found what they say is the strongest evidence yet
      that a mysterious class of stars known as "blue stragglers" are the
      result of stellar cannibalism.

      Blue stragglers are found throughout the universe in globular clusters
      — which typically are collections of about 100,000 stars, tightly
      bound by gravity. Because all the stars in these clusters are thought
      to have been born at the same time, they should all be the same age,
      but blue stragglers appear to be younger than their cluster peers.

      The origin of these strange, massive stars has been a longstanding
      mystery, said study leader Christian Knigge of Southampton University
      in England.

      "The only thing that was clear is that at least two stars must be
      involved in the creation of every single blue straggler, because
      isolated stars this massive simply should not exist in these
      clusters," Knigge added.

      Since these oddball stars were first discovered more than half a
      century ago, two competing explanations for their formation emerged:
      "that blue stragglers were created through collisions with other
      stars; or that one star in a binary system was 'reborn' by pulling
      matter off its companion," said study team member Alison Sills of the
      McMaster University in Canada.

      A 2006 study examined the chemical signatures of 43 blue stragglers in
      the globular cluster 47 Tucanae, and found that six of the unusual
      stars had less carbon and oxygen than the others. The anomaly
      indicated that their surface material had been sucked from the deep
      interior of a parent star in a binary system.

      The new study, detailed in the Jan. 15 issue of the journal Nature,
      provides even more evidence in favor of the stellar cannibalism idea.

      The researchers looked at blue stragglers in 56 globular clusters and
      found that the total number of blue stragglers in a given cluster
      didn't match the predicted collision rate – dispelling the theory that
      blue stragglers are created through collisions with other stars.

      But there was a connection between the total mass contained in the
      core of the globular cluster and the number of blue stragglers
      observed within it. Since more massive cores also contain more binary
      stars, the researchers could infer a relationship between blue
      stragglers and binaries in globular clusters. This conclusion is also
      supported by preliminary observations that directly measured the
      abundance of binary stars in cluster cores.

      "This is the strongest and most direct evidence to date that most blue
      stragglers, even those found in the cluster cores, are the offspring
      of two binary stars," Knigge said. Though there is still plenty of
      research on these stars to do.

      "In our future work we will want to determine whether the binary
      parents of blue stragglers evolve mostly in isolation, or whether
      dynamical encounters with other stars in the clusters are required
      somewhere along the line in order to explain our results," Knigge said.

      The study was funded in part by the United Kingdom's Science and
      Technology Facilities Council.
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