*Edit*
Thank you to everyone for the enlightening responses, I’ve learnt many many things and many have them have been in such clear terms that a giant idiot like myself has been able to understand.
The internet is excellent at times.
In: Physics
Think of this way: You throw a ball vertically up on Earth.. It goes a fair distance then falls back down on the ground. You need to throw it at 11.8 km/s or more for the ball to “escape” Earth and go into Space (I’m ignoring air resistance here).
Similarly, on Moon, you’d need to throw the ball at 2.38km/s, since Moon’s gravity is less than Earth.
This is known as the Escape Velocity.
For our Sun, the Escape Velocity is 615km/s, ie, anything coming out of the Sun slower than that will “fall” back into the Sun.
Escape Velocity also depends upon your distance from the gravitation source(center of the cosmological body, usually). So if you throw the ball from an airplane 35,000 feet in the air, the escape velocity required will be slightly low.
Now think of this way: Event Horizon is the boundary _around_ the black hole where the escape velocity is 3×10^5 km/s. Does this number look familiar to you? It’s the velocity of light. It’s also the Universal cosmological limit, meaning nothing can travel faster than that.
You can work out the next conclusion on your own but I’ll write it here: Since the escape velocity of a black hole at event horizon is “c”, nothing escapes it, not even light.
(Simplified explanation of course)
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