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How many stars in our galaxy if they had the mass of our Sun.

  • Thread starter balletgirl
  • Start date
  • #1
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Homework Statement



The Sun rotates about the center of the Milky Way Galaxy at a distance of about 3.00x10^4 light years from the center (1ly= 9.50x10^5 m). If it takes about 200 million years to make one rotation, estimate the mass of our galaxy. Assume the mass distribution of our galaxy is concentrated mostly in a central uniform sphere. If all the stars had about the same mass as our Sun, how many stars would there be in our galaxy?


Homework Equations



I have no clue, the most common equation I use is g=GM/r^2 and a=v^2/r.

The Attempt at a Solution



I do not know where to start.
 

Answers and Replies

  • #2
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Treat the galaxy as if it was a planet that the sun was orbiting.
 
  • #3
Char. Limit
Gold Member
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Well, g is just gravitational acceleration, and is the a in a=v^2/r... but there's an equation missing.


[tex]a=\frac{4 \pi^2 r}{T^2}[/tex]
 
  • #4
36
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Okay, so I did T= 200,000,000 yrs = 6.31x10^15 s
& R= 2.85x10^20

a=4pi^2*r/T^2
a= 4(3.14)^2*(2.85x10^20)/(6.31x10^15s)
a=39.4(2.85x10^20)/3.98x10^31
a= 2.81x10^-10

I doubt this is right since it is negative
 
  • #5
Char. Limit
Gold Member
1,204
14
No it's not... the exponent is negative, but the number is positive, just very small. And it should be small...
 

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