Black Holes
Black Holes is what forms when a huge star dies and its pull grows so strong that not even light gets out.
Think of it this way
A drain in a sink pulls water toward its center. As water gets closer, it moves faster and faster. Right at the drain, the pull is so strong that nothing flows back out. A black hole works the same way — its center pulls so hard that even light gets sucked in and cannot escape.
Explaining black holes by grade level
Think of a drain in a bathtub. Water swirls down and cannot come back up. A black hole works like that in space. A giant star falls in on itself, and its pull is so strong that even light gets trapped.