Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Finding the mass of a super-massive Black Hole?

  1. May 20, 2014 #1
    Hi, I am not too sure where to post this. I am studying for my astrophysics final and I came across this question which is pretty easy ( I think) but I can't seem to find the answer...

    S2 is observed to be one of the brightest stars orbiting the black hole at the center of Milky Way. It has period of 15 years and orbit of 950 A.U.

    a) Find the mass of the super-massive black hole
    b)find its event horizon.

    I can do b ( can't find the schwarzchild radius without the mass though). For a, I thought of using the relationship of T^2=a^3 to find my semi major axis to then find my mass with M=A^3/P however that didn't work. I'm not too sure what to use anymore.
  2. jcsd
  3. May 20, 2014 #2


    User Avatar
    Science Advisor
    Gold Member

    This is a homework-type question. You should post it in the homework section.

    Why do you want to use the first equation? Both variables are given in the question. The second equation is incorrect(period should be squared).

    Additionally, you're using T in the first, and P in the second, a in the first and A in the second, where each pair means the same thing. It's good to be consistent in notation.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook