A massive star starts to collapse when it exhausts its nuclear fuel and can no longer counteract the inward pull of gravity.

The crushing weight of the star’s overlying layers implodes the core, and the star digs deeper into the fabric of space-time.

Although the star remains barely visible, its light now has a difficult time climbing out of the enormous gravity of the still-collapsing core.

The star passes through its event horizon and disappears from our universe, forming a singularity of infinite density.

Pile enough matter into a small enough volume and its gravitational pull will grow so strong that nothing can escape from it. That includes light, which travels at the absolute cosmic speed limit of 186,000 miles per second. In a stroke of descriptive genius, physicist John Wheeler named these objects “black holes.” The radius of a black hole is called the event horizon because it marks the edge beyond which light cannot escape, so any event taking place inside the event horizon can never be glimpsed from outside—in effect, the inside of the black hole is cut off from our universe. It has even been speculated that black holes could be pathways into other universes. Gravity is so strong at the center of a black hole, that even Einstein’s gravitational laws must break down. The theory that governs the incredibly dense matter and strong gravitational fields at the center of a black hole is not yet known.”