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At the Galaxy's Core

  1. May 26, 2008 #1
    1. The problem statement, all variables and given/known data

    Astronomers have observed a small, massive object at the center of our Milky Way galaxy. A ring of material orbits this massive object; the ring has a diameter of about 15 light years and an orbital speed of about 200 km/s. Take the distance of one light year to be 9.461 X 10^15 m. Mass of object = 4.26 X 10^37 kg. Speed of light (c) = 3 X 10^8 m/s. G = 6.67 x 10^(-11).

    Many astronomers believe that the massive object at the center of the Milky Way galaxy is a black hole. If so, what is its Schwarzschild radius R_S?

    2. Relevant equations

    From Wikipedia, I got the equation for the Schwarzschild radius to be R_S = [2Gm]/c^2.

    3. The attempt at a solution

    Using the above equation and the above constants, I got 1.89 x 10^19 m, which is wrong.

    Other wrong answers: 1.90×10^19 and 1.89x10^35.

    Any help would be appreciated! Thanks!
  2. jcsd
  3. May 26, 2008 #2


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    Well it looks like you divided by c instead of c^2.
  4. May 26, 2008 #3
    Doh! Thanks so much.
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