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Yahoo! News Story - New Observations Detail Milky Way's Big Black Hole - 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: New Observations Detail Milky
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      Mark Holmes (mahtezcatpoc@...) has sent you a news article.
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      New Observations Detail Milky Way's Big Black Hole - Yahoo! News

      http://news.yahoo.com/s/space/20081210/sc_space/newobservationsdetailmilkywaysbigblackhole

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    • mahtezcatpoc
      ... http://news.yahoo.com/s/space/20081210/sc_space/newobservationsdetailm ilkywaysbigblackhole New Observations Detail Milky Way s Big Black Hole Jeanna
      Message 2 of 2 , Dec 10, 2008
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        --- In thefixedstars@yahoogroups.com, Mark Holmes <mahtezcatpoc@...>
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        ilkywaysbigblackhole


        New Observations Detail Milky Way's Big Black Hole
        Jeanna Bryner
        Senior Writer
        SPACE.com – Tue Dec 9, 7:31 pm ET

        Like ballerinas pirouetting around an invisible leader, a collection
        of stars orbits our galaxy's gravity sink, or black hole. New
        infrared images of the cosmic dance confirm that this supermassive
        black hole weighs as much as 4 million suns.


        Supermassive black holes can weigh as much as a billion suns or more
        and are thought to reside at the centers of most, if not all,
        galaxies. They can't be seen, because their gravity is so powerful it
        traps even light, but astronomers infer their presence by watching
        the motions of stars and gas around them.


        Over a period of 16 years, beginning in 1992, researchers monitored
        28 stars orbiting the Milky Way's central region, where the
        supermassive black hole called Sagittarius A* is thought to lurk.


        By watching how the central stars orbited Sagittarius A*, to which
        they are gravitationally bound, the researchers inferred properties
        of the black hole itself, such as mass and distance. They found that
        at least 95 percent of the mass affecting the stars must be within
        the black hole. Results gave a precise distance of 27,000 light-years
        from Earth to the presumed black hole. One light-year is the distance
        light will travel in a year, or about 6 trillion miles (10 trillion
        km).


        "Undoubtedly the most spectacular aspect of our long-term study is
        that it has delivered what is now considered to be the best empirical
        evidence that supermassive black holes do really exist," said team
        leader Reinhard Genzel of the Max-Planck-Institute for
        Extraterrestrial Physics in Germany.


        The new images also reveal common properties among the orbiting
        stars. For instance, the team found the innermost stars trek around
        the black hole in random orbits, while six of the 28 stars, which
        reside farther out, orbit the black hole in the same plane, just as
        our planets mostly do around the sun.


        One particular star, known as S2, orbits the Milky Way's center so
        fast that it completed one full revolution within the study's 16-year
        period.


        The researchers hope to continue to study the dancing stars to solve
        a long-held riddle as to how such stars ended up in their orbits
        about Sagittarius A*. They are too young to have migrated far, and
        scientists think it's improbable the stars formed in their current
        orbits where they'd be exposed to the extreme tidal forces of the
        black hole.


        One explanation put forth recently is that the stars formed out of
        material that survived after a gas cloud plunged in toward the
        central black hole. This scenario was based on computer simulations.
        The researchers suggest that the six stars orbiting in a disk formed
        about 6 million years ago in this gas-cloud scenario.


        The innermost stars could have once been in pairs, said lead
        researcher Stefan Gillessen, also of the Max-Planck-Institute. And so
        when the binary stars got too close to the supermassive black hole,
        the gravitational energy may have been shuffled around between the
        stars. In that way, one member of the pair would've been kicked out
        while the other remained. These innermost stars — each missing a
        partner — are estimated to be about 50 million years old.


        The recent finding involved observations in 1992 with the SHARP
        camera aboard the European Southern Observatory's New Technology
        Telescope at the La Silla observatory in Chile; and more recent
        observations using instruments aboard ESO's Very Large Telescope.
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