What if you fell into a black hole?
It depends a lot on which one.
Horizon Station
Two black holes, one research station and a daughter who reads the safety manual.
1. Pip
Horizon Station orbited far out from two black holes. The small one, ten times the Sun's mass, the crew nicknamed Pip. The giant one, four million Suns, sat at the heart of the galaxy like a sleeping god. Ishita's mother ran the station's probes. Ishita, fourteen, read the safety manual for fun.
Rule one, in red: NEVER APPROACH PIP. 'But it's tiny,' Ishita said. Its event horizon was only about 30 km across. 'That's exactly the problem,' her mother said.
2. The Probe
They watched a test probe fall towards Pip. Long before it reached the edge, its nose started pulling ahead of its tail. Near a small black hole, gravity changes so steeply that the front of an object is pulled far harder than the back.
At the horizon, the difference across a two-metre object would be tens of millions of times Earth's gravity. On the screen, the probe stretched into a long thin thread and was gone. 'Spaghettification,' said her mother. 'That's the real word.' Ishita didn't laugh.
3. The Giant
The giant was different. Its horizon was about 24 million kilometres across, wide enough to swallow the orbit of Mercury. So far from its centre, gravity changed only gently across a small object. A person could drift across that edge and feel nothing at all: no stretch, no wall, no warning.
That was what frightened Ishita most. There would be no moment that felt like falling in. Just an ordinary instant after which no signal, not even light, could ever come back out.
4. The Fading Signal
They sent a second probe towards the giant, broadcasting a steady beep. As it approached the horizon, the beeps came further and further apart, and the probe's light shifted from white to red to infrared. Time near the horizon was running slow compared with the station's.
The probe never seemed to cross. It just faded, frozen at the edge, until the instruments couldn't see it any more. Somewhere, the probe's own clock had ticked on and carried it inside. Ishita wrote one line in her journal: 'Both stories are true.'
The end. Now see the science that the story is built on.
See it happen
What would happen, step by step
From a safe distance, a black hole pulls just like any other object of the same mass. If the Sun were replaced by a black hole of the same mass, Earth's orbit wouldn't change. It would just get very cold.
The science behind it
The point of no return
Event horizon radius R_s = 2GM ÷ c² ≈ 2.95 km × (mass in Suns)
A black hole's event horizon is the distance at which the escape speed equals the speed of light. Inside it, nothing can get out. A black hole of 10 Suns has a horizon about 30 km in radius; Sagittarius A*, at the centre of our galaxy, has about 4 million Suns' worth and a horizon about 12 million km in radius.
Tidal forces: why size matters
Stretch across a body Δa ≈ 2GM L ÷ r³
What hurts is not gravity itself but the difference in gravity from your head to your feet. At the horizon of a 10-Sun black hole, that difference across a 2 m body is about 2 × 10⁸ m/s², over 20 million times Earth's gravity. At Sagittarius A*'s horizon it is about 0.001 m/s², far less than you'd notice. Bigger black holes are gentler at the edge.
Frozen at the edge
General relativity says clocks run slower in strong gravity. To a faraway observer, a falling object's clock seems to slow almost to a stop at the horizon, and its light is stretched to longer and longer wavelengths until it can't be seen. The falling object's own clock runs normally, and it crosses in a finite time. Both descriptions are correct; they belong to different observers.
In one line: Tidal force depends on how quickly gravity changes with distance. For bigger black holes, the event horizon is so far from the centre that the change across your body is small, which is why the biggest black holes are the 'gentlest' to fall into.
The black hole information paradox →Think about it
Why might a supermassive black hole be 'safer' to fall into than a small one, even though both are deadly in the end?