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Re: Yahoo! News Story - Collisions Fuel Black Hole Feeding Frenzies - Yahoo! New

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  • mahtezcatpoc
    ... http://news.yahoo.com/s/space/20080623/sc_space/collisionsfuelblackholefeedingfrenzies Collisions Fuel Black Hole Feeding Frenzies Clara Moskowitz Staff
    Message 1 of 1 , Jun 24 9:13 PM
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      http://news.yahoo.com/s/space/20080623/sc_space/collisionsfuelblackholefeedingfrenzies


      Collisions Fuel Black Hole Feeding Frenzies

      Clara Moskowitz
      Staff Writer
      SPACE.com Mon Jun 23, 4:15 PM ET

      Black hole feeding frenzies are fueled by galactic collisions,
      suggests a new study that confirms astronomers' suspicions.


      Astronomers have had their eyes on a certain class of galaxies that
      appear to contain central black holes that gorge on gas and dust. So
      far, scientists have been unsure what triggers these giant meals, but
      new radio observations may help explain how they work.

      Seyfert galaxies are a type of galaxy known as Active Galactic Nuclei
      (AGN), thought to host supermassive black holes in their centers.
      Seyferts are slightly tamer versions of the extremely luminous AGN
      called quasars and blazars.

      Scientists guessed that recent interactions with neighboring galaxies
      might have stirred up Seyferts' gas and dust and propelled it toward
      their giant black holes. But when optical telescopes observe Seyferts
      in light visible to the human eye, the Seyferts show no sign of close
      encounters with other galaxies.

      Now astronomers have used the Very Large Array (VLA) telescope to
      photograph these objects in radio light, and found that the majority
      of Seyferts do indeed seem to have recently collided with a neighbor.
      For comparison, the researchers observed non-Seyfert galaxies and
      found that very few showed signs of an interaction.

      "This comparison clearly shows a connection between close galactic
      encounters and the black-hole-powered activity in the cores," said
      Ya-Wen Tang, who began this work at the Institute of Astronomy &
      Astrophysics, Academia Sinica (ASIAA), in Taiwan and now is a graduate
      student at the National Taiwan University. "This is the best evidence
      yet for the fueling of Seyfert galaxies. Other mechanisms have been
      proposed, but they have shown little if any difference between
      Seyferts and inactive galaxies."

      The VLA telescope was able to study the galaxies' hydrogen gas by
      observing the radio waves emitted by hydrogen atoms. The hydrogen gas
      in many Seyferts left a clear signal of being disturbed by a collision
      with another galaxy.

      "Our results show that images of the hydrogen gas are a powerful tool
      for revealing otherwise-invisible gravitational interactions among
      galaxies," said Jeremy Lim, also of ASIAA. "This is a welcome advance
      in our understanding of these objects, made possible by the best and
      most extensive survey ever made of hydrogen in Seyferts."

      The new study helps scientists better understand these violent
      systems, where gas and dust swirl around dense black holes that
      eventually gobble up the incoming material.

      "The VLA lifted the veil on what's really happening with these
      galaxies," said Cheng-Yu Kuo, a graduate student at the University of
      Virginia. "Looking at the gas in these galaxies clearly showed that
      they are snacking on their neighbors. This is a dramatic contrast with
      their appearance in visible starlight."

      --End story.
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