If we answer briefly, he will die. More elaborately—it’s not exactly known what will happen. Science can only speculate. But you can be sure that nothing particularly pleasant will occur.
At a respectful distance, a black hole behaves like a star of similar mass—you can achieve a stable orbit around it and remain there for years. Scientists suggest that habitable planets might even exist there. But the closer you get to the black hole, the more problems you’ll encounter.
Radiation Will Kill the Person
If you think that a black hole will harm a person only when they cross the event horizon (the boundary around the black hole from which even light cannot escape), you are mistaken. The difficulties will start much earlier—and they will be literally deadly.
Black holes are rarely isolated. Typically, they are surrounded by a massive amount of matter—gas left over after the black hole consumed some star. This gas orbits at high speed, gaining enormous kinetic energy and heating to extreme temperatures.
This rapidly spinning, scorching-hot structure around the black hole is called the accretion disk.
Viewers of the movie Interstellar are familiar with what an accretion disk should look like. The black hole itself is invisible, as it absorbs all the light that falls on it, but the whirlpool of matter around it is visible. The accretion disk is the glowing orange structure that telescopes from the Event Horizon Telescope project captured in April 2019.
Accretion disks of black holes emit powerful electromagnetic radiation. The energy of X-rays and gamma rays exceeds that of visible light by a factor of a trillion.
Additionally, theoretically, the black hole itself might emit Hawking radiation. However, astrophysicists are still uncertain about this and the radiation’s power is negligible.
All of these streams of charged particles, which the black hole hurls hundreds of light-years around it, are unlikely to be healthy for anyone. The celestial object will kill a person with regular radiation long before any distortions of space or time come into play.
Accretion Disk’s Material Will Burn Them
Suppose the astronaut takes care of radiation safety—by, for example, wearing a lead-lined suit over their spacesuit—and continues their determined fall toward the mysterious depths of the black hole. However, another obstacle awaits: the aforementioned accretion disk.
It’s composed of extremely hot gas. The disk heats up as gas particles collide with each other, spiraling around the black hole at breakneck speeds. Kinetic energy turns into thermal energy—substantial thermal energy.
Matter near a typical black hole can reach temperatures of millions or even trillions of kelvins. That’s significantly higher than, for example, the temperature of our Sun: 5,778 K on its surface, 15 million K at its core. It’s probably unnecessary to remind you that flying through streams of scorching plasma is unsafe. If radiation doesn’t kill a person, the high temperature certainly will.
In fact, accretion disks of supermassive black holes in the centers of galaxies are among the brightest objects in the cosmos. They’re called quasars. The hottest of them, J043947.08+163415.7, burns with the heat of 600 trillion Suns.
Periodically, black holes send relativistic jets—plasma streams moving at near-light speed—into the universe, usually in pairs, launched from the poles in opposite directions.
Astrophysicists are still debating why this happens, but it seems magnetic fields around the black hole do something interesting with the gas in the accretion disk. A jet can erupt continuously for 10 to 100 million years.
So, while falling into a black hole, a person should avoid the poles to not get caught in a relativistic jet.
They Will Be “Spaghettified”
Given all this, it might be better to travel into a black hole without an accretion disk. Such black holes exist—if there are no nearby stars from which to siphon gas. In other words, the black hole has already consumed everything nearby.
For example, the black hole at the center of the galaxy Markarian 1018 has absorbed all the matter around it and is left without nearby gas. Astrophysicists call these black holes “starving.” Poor things.
Or take the supermassive black hole Sagittarius A* at the center of our Milky Way—it has an extremely small, barely noticeable disk. That’s why it’s so hard to observe.
In such a case, it’s possible to approach the event horizon of a black hole without encountering streams of hot plasma.
The problems that will arise for the astronaut beyond this point will depend on the size of the black hole.
If the person is falling toward a black hole with, say, the mass of our Sun (which is 332,946 times greater than Earth’s), the following will happen.
As they approach this intriguing celestial object, the gravitational force acting on them will increase. At a certain distance, the gravitational pull on their feet will be many times stronger than the pull on their head. This difference is called a “tidal force.”
The consequences of this force are described by physicist Neil deGrasse Tyson in his book Death by Black Hole and Other Cosmic Quandaries.
First, the tidal forces of the black hole will tear the astronaut in half right at the torso (if they are falling feet first, not sideways). Then their legs and torso will be torn in half again. This will continue exponentially until even the atoms of which the victim is composed are broken down into elementary particles. These particles will then pass beyond the event horizon.
Earth also exerts a tidal force on your body, but it’s not strong enough to tear you apart, so don’t worry.
That’s it. This phenomenon is humorously called “spaghettification.” Typically, black holes are spaghettify stars, but they can do the same to humans.
Something Terrible Will Happen, but We Won’t Know Exactly What
Tidal forces, as Neil Tyson explains, grow stronger the larger the object relative to its distance from the center of the black hole. This means that a small black hole will tear the astronaut to pieces and break them down into atoms before they even reach the event horizon.
However, if the black hole is massive enough and has a huge radius, its tidal forces will start stretching the traveler only after they have crossed the event horizon.
At that point, the person might even survive, says physicist Leo Rodriguez, because the event horizon is not a physical barrier, just the boundary of the black hole’s gravitational influence, beyond which even light cannot escape.
Before passing the event horizon, the traveler might witness the light of all surrounding stars distort and then compress into a point behind them, which would first turn red, then white, and finally blue. This happens due to the black hole’s gravitational effect on the wavelengths of light passing by (called “blueshift”).
But no one can say for sure what happens beyond the event horizon. The problem is that the familiar laws of physics no longer apply there. Scientists can only speculate about what happens to matter in a black hole.
Most likely, according to Neil Tyson, the person will be spaghettified, just not before the event horizon but afterward. Then what’s left of the traveler will fall into the singularity—the point of infinite density at the center of the black hole.
So, there will be no bookcases or Morse code messages sent to a daughter, as in Interstellar.
