Here's why:

* Gravity: Black holes have incredibly dense matter packed into a tiny space. This creates a gravitational pull so strong that nothing, not even light, can escape its grasp.

* Event Horizon: The boundary around a black hole where the escape velocity exceeds the speed of light is known as the event horizon. Anything crossing this boundary is trapped forever.

While we can't directly see black holes, we can observe their effects on surrounding matter and use sophisticated telescopes to detect them.