Understanding Black Holes: Comparing Mass Calculation Methods

[Eternalmetal]

If I were determining the mass of a black hole, would I do it the same way as if it were a planet?

 

[Vazier]

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

 

[malawi_glenn]

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.

 

[andrewj]

If I were determining the mass of a black hole, would I do it the same way as if it were a planet?

no i think maybe you have to work back from its entropy

 

[malawi_glenn]

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

 

[Chris Hillman]

If I were determining the mass of a black hole, would I do it the same way as if it were a planet?

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 black hole-blackhole or neutronstar-neutronstar binary this works pretty well.

Andrewj's suggestion is nonsense.

 

[Vazier]

actually i was checking out the thing abut the using enthropyto find the mass of the black hole and apparently it is possible ( i never knew that till now myself :uhh:) but i found in this link that it is possible

http://www.upscale.utoronto.ca/GeneralInterest/Harrison/BlackHoleThermo/BlackHoleThermo.html

using the entropy we find the heat of the black hole which is actually the mass-energy of the black hole

 

[malawi_glenn]

yes vazier, in theory. But not in practice.

 

[Chris Hillman]

the heat of the black hole

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.

 

[Vazier]

i see... thanks for telling that... i will go through a few more articles to understand the thing better

 

[rubecuber]

i agree with Vazier

 

[Chris Hillman]

i agree with Vazier

That's too bad, since as already pointed out he made at least two major errors in what he wrote.

 

[Vazier]

2 major errors?

 

[Chris Hillman]

Yes--- reread what you wrote and then reread my comment.

 

[Vazier]

okay ... i got it i guess XD