What falling in would be like

Nobody has fallen into a black hole and reported back, and nobody ever will. Everything on this page comes from Einstein's theory, which has passed every test we've given it outside black holes, followed all the way to its conclusions. Keep that in mind. It's a very good guess, not a travel report.

The edge isn't a wall

The boundary you can't come back from is called the event horizon. It's not a surface. There's nothing there to hit, no glowing shell, no sign. It's a point of no return, like the spot on a river above a waterfall where the current gets faster than you can swim. You can drift past it without noticing, and after that, every direction you could possibly move leads further in.

Stretched like spaghetti

Gravity gets stronger the closer you are. Fall feet first and your feet are a little closer than your head, so they're pulled a little harder. On Earth the difference is far too small to feel. The same effect raises the ocean tides, because the Moon pulls harder on the near side of Earth than the far side.

Near a small black hole that difference becomes brutal. Take one about 10 times the Sun's mass, with a horizon roughly 60 kilometers across. Long before you reached the horizon, perhaps a thousand kilometers out, the pull on your feet would outstrip the pull on your head so badly that you'd be stretched long and thin and torn apart. Physicists really do call this spaghettification.

This part isn't only theory. Astronomers have watched whole stars wander too close to supermassive black holes and get shredded. The flare of light from a star being pulled apart can last for months.

Bigger is gentler

Here's the surprise. A supermassive black hole is kinder at the edge than a small one.

The stretch depends on how quickly gravity changes over the length of your body. A huge black hole has a huge horizon, and at that distance from the center, gravity changes very slowly over 2 meters. At the horizon of Sagittarius A*, the stretch would be too gentle to notice. You'd cross the point of no return in one piece, maybe without realizing it.

Play or scrub toward the horizon, then switch masses. At a fixed number of horizon radii, tidal strength falls with the square of the black hole mass.

Your luck runs out later. Inside, the theory says you're carried toward the center, and the stretching grows until it tears you apart there too. For our galaxy's black hole, the whole trip from horizon to center would take at most about a minute by your own watch. For the far heavier one in M87, more like a day.

What's at the bottom?

The math says all the mass ends up crushed into a single point of infinite density, called a singularity. Most physicists don't believe that's literally true. When a theory starts producing infinities, it usually means the theory has stopped working. Something else takes over at the center, probably a theory that joins gravity with quantum physics. Nobody has one that works yet.