Why is it not possible to see a black hole?

Black hole is a pitch-black invisible patch having immensely strong gravity from which neither matter nor radiation, including light, can escape.

Speaking in terms of space-bound rockets instead of the rays of light, the former must achieve the speed of 11.18 kilometers per second in order to escape from the Earth’s gravitational force to enter gravitation-free environment of the space. This speed is known as escape velocity. Rockets launched from Jupiter and the Sun must achieve velocity of 60.8 and 640 kilometers per second respectively in order to escape from their much greater gravitational force. Similarly, the rocket can not leave tremendously strong gravitational force of a neutron star if its escape velocity is less than 160,000 kilometers per second! Let’s assume that such a velocity is possible, at least theoretically; but the escape from black hole will require escape velocity more than 299,792 kilometers per second which is the speed of light! Hence, neither man-made rocket nor rays of light can emerge from a black hole. Since light of the black hole remains confined within it, it is just not possible to see a black hole even with the most powerful telescope.

More reading:
Black hole (Wikipedia)
Escape velocity (Wikipedia)

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