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

Simple Black hole question

  1. Nov 13, 2007 #1
    If I were determining the mass of a black hole, would I do it the same way as if it were a planet?
     
  2. jcsd
  3. Nov 13, 2007 #2
    depends on what way you do it to find the mass of the planet.... but i think the mass of a black hole is found using the gravitational field it exerts on the surroundings
     
  4. Nov 13, 2007 #3

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    If you have the BH in a binary system (with an ordinary star for example), then yes, you measure the mass of the BH by just calculate it from the obseravional data using keplers law and so on.
     
  5. Nov 13, 2007 #4
    no i think maybe you have to work back from its entropy
     
  6. Nov 14, 2007 #5

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    Go back in history, how you deduced for the first time that black holes exists. You use planetary motion, keplers laws etc.
     
  7. Nov 14, 2007 #6

    Chris Hillman

    User Avatar
    Science Advisor

    As Malawi said, in general you would use Kepler's laws just as for any object. Even in the case of a fairly tightly orbiting blackhole-blackhole or neutronstar-neutronstar binary this works pretty well.

    Andrewj's suggestion is nonsense.
     
  8. Nov 15, 2007 #7
  9. Nov 15, 2007 #8

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    yes vazier, in theory. But not in practice.
     
  10. Nov 15, 2007 #9

    Chris Hillman

    User Avatar
    Science Advisor

    No; you'd better read that again. (Hint: extensive versus intensive quantities!)

    As Malawi said, using Kepler is a practical method. No-one has yet detected (or hopes to detect) the Hawking radiation from any black hole!--- it's much too weak.
     
  11. Nov 16, 2007 #10
    i see...... thanks for telling that.... i will go through a few more articles to understand the thing better
     
  12. Nov 16, 2007 #11
    i agree with Vazier
     
  13. Nov 17, 2007 #12

    Chris Hillman

    User Avatar
    Science Advisor

    That's too bad, since as already pointed out he made at least two major errors in what he wrote.
     
  14. Nov 17, 2007 #13
    2 major errors?
     
  15. Nov 17, 2007 #14

    Chris Hillman

    User Avatar
    Science Advisor

    Yes--- reread what you wrote and then reread my comment.
     
  16. Nov 18, 2007 #15
    okay ... i got it i guess XD
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Simple Black hole question
  1. Black hole question (Replies: 4)

Loading...