You can easily compress a football to the size of an olive. If you release it, the football returns to its original size; right? However if you compress Earth to the size of an olive Earth becomes a Black Hole. If you release it, Earth will not return to its original size. You will not be able to release your hands. Gravity would have grown so much that not even light can escape.

The largest Black Hole discovered weighs a whopping 18 billion solar masses, and is as big as our solar system. Although light cannot escape from inside any Black Hole, matter falling into Black Holes emit X-Ray. Some emissions are equivalent to a few billion supernovae (exploding stars)!!! We call these systems Quasars.