News ... stars observed by the Sloan Digital Sky Survey, D

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Our galaxy's double halo
http//www.astronomy.com December 12, 2007

• Department of Physics
• National Tsing Hua University
• G.T. Chen
• 2007/12/20

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News

• Using 20,000 stars observed by the Sloan Digital
  Sky Survey, D. Carollo et al. have discovered
  that the outer Milky Way is a mix of two distinct
  components rotating in opposite directions ---
  There are two stellar components in the halo of
  the Milky Way.

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News

• By examining the motions and chemical
  compositions of the stars, they see that the
  inner and outer halos are quite different.
• The inner-halo component dominates the population
  of halo stars found at distances up to 1015 kpc.
• The outer-halo component dominates in the regions
  beyond 1520 kpc.

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• The inner halo formed first from the collision of
  smaller but massive galaxies that rotated with
  the Galaxy.
• The outer halo formed later from small galaxies
  orbiting the Milky Way in the reverse direction.
• ?These were split apart by the Milky Way's
  gravitational forces, dispersing their stars into
  the halo.

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References

• http//www.astronomy.com
• December 12, 2007
• Nature 450, 1020 - 1025 (13 Dec 2007)

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gtgtThank youltlt
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News

• a disk of stars orbiting around the center of the
  Galaxy at an astounding 500,000 miles per hour.
• The inner halo, located well outside the disk,
  rotates in the same direction, but more slowly,
  at 50,000 miles per hour.
• The outer halo, the most remote of these
  components, spins in the opposite direction, at
  about 100,000 miles per hour.

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News

• inner-halo stars contain three times more heavy
  atoms than outer-halo stars
• Fe/Hinner-1.6 ,Fe/Houter -2.2

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• The patterns of chemical elements provide clues
  to the properties of stars that formed in the
  first billion years after the Big Bang.