...in explaining to an 8 year old:
What is an event horizon ?
It is a boundary in spacetime.
Beyond this boundary you can no longer escape gravitational pull.
It is the boundary to an area in space which is so dense that no light,
matter can escape it's gravitational field.
Beyond the event horizon you are caught in the gravitational field of a black hole, a super dense area in space.
At the event horizon the escape velocity is the speed of light.
All galaxies have supermassive black holes at their centre.
My dinner table discussions with my sons revolved around “would you rather be machine gunned to death or eaten by a shark? Who would win in a fight between Spiderman and Superman? (everyone knows Spiderman of course)” My wife despaired. Black holes didn’t come-up.