The Place Where Light Cannot Escape

A star collapsing until what’s left of it pulls so hard that not even light climbs back out.

Before you start. You need two things already in your head: gravity is mass pulling on mass, harder the closer and heavier things get, and nothing outruns light. Both get a one-line reminder the moment this note leans on them.

The idea in 30 seconds

A black hole is what’s left when enough mass collapses inside a boundary not even light climbs back out of.
That boundary, the event horizon, isn’t a wall - past it, every direction leads further in, like a waterfall’s edge.
Schwarzschild worked out its exact size in 1915; Michell guessed the same number in 1783 with physics wrong in almost every detail.
The equations predict a dimensionless point at the centre, the singularity - a sign gravity’s theory runs out of road there, not proof something infinitely small exists.
Spaghettification happens far outside the horizon for a small black hole and deep inside for a giant one - never right at the edge.
Every black hole detected is absorbing more heat than it gives off, so it’s growing, not shrinking; real evaporation can’t start for 255 billion years.

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