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

1. Dec 8, 2014

Lamdbaenergy

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?

2. Dec 8, 2014

Bandersnatch

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.

3. Dec 8, 2014

Lamdbaenergy

Nope, got nowhere near the right mass. I tried for a solar mass black hole, too. Any other suggestions?

4. Dec 8, 2014

Bandersnatch

Can you show what you did exactly?

5. Dec 8, 2014

Lamdbaenergy

2GR/c^2, then I tried R^2c^2/2G

6. Dec 8, 2014

Bandersnatch

Neither of those is correct. Start with the Schwartzschild radius formula $r_s=\frac{2Gm}{c^2}$ and isolate the mass on one side.

7. Dec 9, 2014