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Re: Yahoo! News Story - New Observations Detail Milky Way's Big Black Hole - Yahoo! News

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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 1 of 2 , Dec 10, 2008
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      > New Observations Detail Milky Way's Big Black Hole - Yahoo! News
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      http://news.yahoo.com/s/space/20081210/sc_space/newobservationsdetailm
      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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