Find the mass of a black hole from just its radius?

AI Thread Summary
To find the mass of a black hole using its radius, the Schwarzschild radius formula can be rearranged to isolate mass. The correct formula is r_s = 2Gm/c^2, which allows for the calculation of mass if the Schwarzschild radius is known. Users reported unsuccessful attempts with alternative equations, indicating confusion in the application of the formulas. A specific online calculator was recommended to assist with the calculations. Understanding the correct manipulation of the Schwarzschild radius formula is crucial for accurate mass determination.
Lamdbaenergy
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I know the original schwarzschild formula for finding the radius of the black hole, but what equation can be used to find its mass if you ONLY know its radius?
 
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Can't you use the same formula? Only instead of using mass to find the Schwartzschild radius, use the Schwartzschild radius to find the mass.
 
Bandersnatch said:
Can't you use the same formula? Only instead of using mass to find the Schwartzschild radius, use the Schwartzschild radius to find the mass.

Nope, got nowhere near the right mass. I tried for a solar mass black hole, too. Any other suggestions?
 
Can you show what you did exactly?
 
Bandersnatch said:
Can you show what you did exactly?

2GR/c^2, then I tried R^2c^2/2G
 
Neither of those is correct. Start with the Schwartzschild radius formula ##r_s=\frac{2Gm}{c^2}## and isolate the mass on one side.
 

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