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The Most Distant Star in the Milky Way

  1. Aug 11, 2014 #1
    A star 890,000 light-years away patrols our galactic frontier

    By Ken Croswell, author of The Alchemy of the Heavens

    Just as every planet in the solar system orbits the sun, so every star in the Milky Way orbits the big black hole at our galaxy's center. But how far out does the Milky Way extend? Astronomers are closer to answering that question with the discovery of two remote giant stars. "They're the most distant stars that we've ever seen in our Milky Way," says John Bochanski of Haverford College, the astronomer who found them. The two stars probe an unexplored region of space and should help gauge our galaxy's total mass, which is poorly known.

    Link includes a color photograph of the farthest star: Scientific American
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  3. Aug 11, 2014 #2
    The red giants ULAS J0744+25 and ULAS J0015+01 are an interesting discovery in my opinion.
    The Milky way's main disk span is only about 100,000 light years across, with a central bulge about 25,000 light years in diameter. John Bochanski and his team know these newly found stars are part of the milky way threw their velocity. The stars being at about 775,000 and 900,000 light-years away are about a third of the distance to Andromeda, our neighbor galaxy.
  4. Aug 11, 2014 #3


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    Isn't that much farther away than the LMC and the SMC, and other dwarf galaxies?
  5. Aug 11, 2014 #4


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    'through' not 'threw'
  6. Aug 11, 2014 #5


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    Here is the journal article in case anyone wants to look at technical details:
    The Most Distant Stars in the Milky Way

    John J. Bochanski, Beth Willman, Nelson Caldwell, Robyn Sanderson, Andrew A. West, Jay Strader, Warren Brown
    (Submitted on 9 Jul 2014)
    We report on the discovery of the most distant Milky Way (MW) stars known to date: ULAS J001535.72+015549.6 and ULAS J074417.48+253233.0. These stars were selected as M giant candidates based on their infrared and optical colors and lack of proper motions. We spectroscopically confirmed them as outer halo giants using the MMT/Red Channel spectrograph. Both stars have large estimated distances, with ULAS J001535.72+015549.6 at 274±74 kpc and ULAS J074417.48+253233.0 at 238 ± 64 kpc, making them the first MW stars discovered beyond 200 kpc. ULAS J001535.72+015549.6 and ULAS J074417.48+253233.0 are both moving away from the Galactic center at 52±10 km s−1 and 24±10 km s−1, respectively. Using their distances and kinematics, we considered possible origins such as: tidal stripping from a dwarf galaxy, ejection from the MW's disk, or membership in an undetected dwarf galaxy. These M giants, along with two inner halo giants that were also confirmed during this campaign, are the first to map largely unexplored regions of our Galaxy's outer halo.
    7 pages, 2 figures. Accepted and in print by ApJL.
  7. Aug 11, 2014 #6


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    That's true and its a good point.
    The distance to LMC, for example, is 158,200 light years.

    BTW these two very distant stars are not in the galactic plane. They give the (l,b) longitude and latitude coordinates and the latitudes of the two stars are around 20 degrees (i.e. in galactic "Northern" hemisphere) and -60 degrees (in the "Southern")

    As I recall what they call N and what they call S is somewhat arbitrary and doesn't follow any clockwise or counterclockwise rotation rule, but it does allow a rough correspondence with the terrestrial directions but skewed by some 60 degrees. Stuff in the earth's northern sky tends to have a positive b, and things in the earth southern tend to have negative b. However if you took off from the galactic plane and went due north for a good long ways and then looked back or DOWN on the galactic plane you would see rotation going CLOCKWISE.

    So galactic "north" is a lefthand thumb. That is just the way the convention went when the time came to have one. As I recall. Correct me if I'm wrong, anybody.
    Last edited: Aug 11, 2014
  8. Aug 11, 2014 #7
    >.< opps thx
  9. Aug 12, 2014 #8
    From the Scientific American article: "The only other Milky Way member at a comparable distance [to 890,000 light-years] is a small galaxy named Leo I, which orbits ours at a distance of 850,000 light-years."

    And yes, both stars are much farther than the Large and Small Magellanic Clouds, which are respectively 160,000 and 200,000 light-years from Earth. Prior to 1994, the Magellanic Clouds were the closest known satellite galaxies to the Milky Way.
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