What should be the closest approximate radius of a celestial body twice as massive as the sun so that the escape speed from the celestial body is equal to the speed of light? (The mass of sun is 2 10³⁰ Kg , speed of light is 3 10^8 ~m / s , and universal gravitational constant G=7 10⁻¹¹ ~N ~m ^2 / Kg ^2 .)