Question

The condition for a uniform spherical mass m of radius r to be a black hole is [G = gravitational constant and

g = acceleration due to gravity]

• A. $(2Gm/r)^{1/2} \leq c$
• B. $(2Gm/r)^{1/2} = c$
• C. $(2Gm/r)^{1/2} \geq c$
• D. $(gm/r)^{1/2} \geq c$

Answer 1

Answer: (C)

$(2Gm/r)^{1/2} \geq c$

Answer 2

The criterion for a star to be black hole is

$\frac{GM}{c^{2}R} \geq \frac{1}{2}$ or, $\sqrt{\frac{2GM}{R}} \geq c$.