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Calculating mass of Milky way Galaxy

  1. Jul 18, 2015 #1
    I used the ##v^2=MG/R## to calculate mass of milky way.Now ##v=225000## m/s G=6.7 10-11 and r is 16 kpc source (https://upload.wikimedia.org/wikipedia/commons/7/77/Rotation_curve_(Milky_Way).JPG)
    If I plut them I get ##50,625,000,000=v^2## and the other side G=6.6 10-11 and R =49.6 1019 so ##M=v^2R/G## thats equal 50,625,000,000/5.1020.6.6 10-11 which its ≅ 1.534 10-3

    Whats the point which I am missing
     
  2. jcsd
  3. Jul 18, 2015 #2

    PeterDonis

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    You forgot to include R in the numerator of your calculation, and I don't understand where the 5.1020 in the denominator comes from.
     
  4. Jul 18, 2015 #3
    Oh I made a huge mistake now I see it 5 1020 comes from kpc-meter transformation.Then the answer will be 50,625 106*5 1020/6.6 10 -11.Which we get ≅40 10 36 which means 8 106 Msun
     
  5. Jul 18, 2015 #4
    But again it false
     
  6. Jul 18, 2015 #5

    PeterDonis

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    Check your math. I get as a rough answer ##\left( 5 \times 10^{10} \right) \left( 5 \times 10^{20} \right) / \left( 7 \times 10^{-11} \right)##, which comes out to about ##4 \times 10^{41}##, or about ##10^{11} M_{sun}##, which is about right. (As a rule of thumb, when using scientific notation, always adjust the exponent so that the number in front is between 1 and 10. You didn't do that for the ##v^2## factor and I think it confused you.)
     
  7. Jul 18, 2015 #6
    Probably you are right.Thanks for help
     
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