Space SimulatorFall into a black hole

What Happens If You Fall into a Black Hole? A Step-by-Step Journey Past the Event Horizon

Published · Space Simulator

A black hole is a place where gravity is so strong that, past a certain distance, nothing can get back out, not even light. That boundary is the event horizon. So what would actually happen to you if you fell in?

The surprising answer: it depends almost entirely on how big the black hole is. Near a small one you would be torn apart long before you got close. Near a giant one you could drift across the point of no return without feeling anything at all. Let's follow the fall step by step, using real black holes and real numbers.

Three real black holes to fall into

The horizon radius grows in direct proportion to mass: about 2.95 km for every solar mass (the Schwarzschild radius, 2GM/c²).

Step 1: the approach, and the sky starts to bend

Long before anything happens to your body, you would notice the view. A black hole bends light around itself, so the stars behind it are smeared into arcs and rings. The dark disc you see, the black hole's shadow, is about 2.6 times wider than the horizon itself, because light that passes too close is captured. This is exactly the dark centre inside the glowing ring in the Event Horizon Telescope images.

As you fall, the shadow grows larger and larger in your view, and the distorted image of the rest of the sky is squeezed into a smaller part of it.

Step 2: tides, and the problem with small black holes

What kills you is not gravity itself but the difference in gravity across your body. Your feet, closer to the black hole, are pulled harder than your head. This stretching is called spaghettification.

Near a small black hole the effect is brutal. For a 10-solar-mass black hole like Gaia BH1, the stretch across a 2-metre person reaches about 100 g at roughly 1,700 km from the centre, far outside the horizon, and grows to around 20 million g at the horizon. You would be pulled apart into a stream of atoms well before crossing.

Near a supermassive black hole the tides are gentle, because the horizon is so far from the centre. At the horizon of Sgr A*, the stretch across your body is about one ten-thousandth of a g: far less than you feel in a lift. At M87* it is smaller still.

Step 3: crossing the event horizon

Here is the strangest part. If you fall into Sgr A*, nothing special happens at the horizon. There is no wall, no flash, no sign. Your watch keeps ticking normally and you feel nothing unusual. The horizon is not a thing; it is simply the place where every path outward has turned inward.

A friend watching from far away sees a completely different story. Your signals arrive slower and slower, and redder and fainter, as you approach the horizon. They never see you actually cross: you seem to freeze and fade into the darkness. Both views are correct. That is general relativity.

Step 4: the last seconds

Once inside, the future points toward the centre, the singularity, as surely as tomorrow follows today. Firing rockets cannot help; it only gets you there sooner.

How long do you have? Falling in from far away, the time on your own watch between crossing the horizon and reaching the centre is:

Near the end, tidal forces grow without limit even in a giant black hole, and spaghettification finally catches up with you. What happens at the singularity itself is unknown: it marks where our current theories stop working.

So, small or big?

If you ever have to choose, choose big. A small black hole tears you apart outside the horizon. A supermassive one lets you cross the point of no return intact, look around for half a minute, and see a view no one has ever seen.

You can try both right now in the Fall into a Black Hole simulator, which computes the light paths and your clock in real time for Sgr A*, M87* and Gaia BH1.

Frequently asked questions

Would you survive falling into a black hole? Not for long. Near a small black hole, tidal forces would pull you apart before you reached the event horizon. Near a supermassive one like Sagittarius A*, you could cross the horizon unharmed, but nothing can then stop you reaching the singularity, about half a minute later.

What is spaghettification? The stretching of an object by tidal forces: gravity pulls harder on the part of you that is closer to the black hole than on the part farther away, so you are stretched along the line of fall and squeezed from the sides.

Can anything escape once it crosses the event horizon? No. Inside the horizon every possible path, even one taken by light, leads inward. That is what defines the horizon.

How long does it take to reach the singularity? It depends on the black hole's mass. Falling in from far away, about 28 seconds of your own time pass between the horizon and the singularity of Sagittarius A*. For a black hole of 10 solar masses it is about 66 millionths of a second; for M87*, about 12 hours.

Explore it yourself: Fall into a black hole · The sound of gravitational waves · How big are the stars? · Exoplanets and the Milky Way in 3D

Sources

Derived figures are textbook Schwarzschild results: horizon radius 2GM/c² (2.95 km per solar mass); tidal stretch across a body of length L, 2GML/r³; time from horizon to centre for a fall from far away, (4/3)·GM/c³; shadow radius √27·GM/c², about 2.6 horizon radii. Rotation changes these slightly.