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

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  • Mark Holmes
    Mark Holmes (mahtezcatpoc@yahoo.com) has sent you a news article. (Email address has not been verified.) ... Personal message: Oddball 'Blue
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      Oddball 'Blue Stragglers' Are Stellar Cannibals - Yahoo! News

      http://news.yahoo.com/s/space/20090114/sc_space/oddballbluestragglersarestellarcannibals

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    • mahtezcatpoc
      ... http://news.yahoo.com/s/space/20090114/sc_space/oddballbluestragglersarestellarcannibals ... Oddball Blue Stragglers Are Stellar Cannibals Andrea
      Message 2 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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