A black hole is a place in space where gravity pulls so strong that even light can not escape. Gravity is so strong, because the matter has been squeezed into a small space. This can occur when a star dies. Since light can not get out, people can not see black holes. They are invisible.
Black holes have a certain aura about them. They are related to the mass consciousness with a certain mysticism or ultra-mystery around them – terrifying objects that absorb everything within its range – the ultimate devouring, doomsday machine, berserker and weapons of mass destruction all in one.
The property we most associated with black holes is a gravity a function of the mass – the greater the mass, the greater the force of gravity. In connection with this concept is the escape velocity – how fast you need to go to avoid the object gravity will never come back.
If you can not see a black hole, how could you know they actually (as opposed to theoretical) exist? Simple – the black holes have severity and gravity of black holes can influence the matter we can see. So if you see a star going too and fro in orbit, we can not see, then that something is probably a black hole.
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