Here’s What Would Happen If You Walked Through a Black Hole

Black holes are enigmatic yet simplistic astronomical forces at the center of science fiction and scientific discovery alike. At the center of our universe, a supermassive black hole with a mass equivalent to 4 million suns lies: Sagittarius A.

Though humans – at least to our knowledge – have never come into contact with a black hole, the potential encounter has long been a source of both regimented research and casual curiosity. The outcome would depend on many factors, mainly the mass, or size, of a black hole. So, what would happen to our bodies if we walked through one?

Walking Through a Black Hole

In general, the scientific community agrees that if a person were to come into close enough contact with a large black hole, its gravitational pull could cause spaghettification, essentially stretching a person into an “infinitely long and infinitely thin” noodle.

But if a small black hole were to pass through a person, it could send a fatal supersonic shockwave akin to a gunshot wound, destroying tissue and pulling interconnected cells apart as it makes its way through the body.

Then again, a person could die from a black hole’s radiation, which would feel like a fireball burning from the inside out.

There are multiple ways to die by black holes – at least, in theory. But to understand how these forces would affect the human body, first, we must explore the science of black holes.

What Is a Black Hole?

A black hole is a simplistic astronomical feature compared to planets like ours. To describe and characterize Earth, for example, one would need to consider what it is made of, its shape and mass, how much of the planet is covered in water, and the makeup of its atmosphere. Black holes, on the other hand, are characterized by three things: mass, spin, and charge.

Sarah Gallagher, a professor of astrophysics at Western University in Ontario, Canada, said that two black holes of the same mass, spin, and charge are indistinguishable from one another.

“They’re just the same black hole,” says Gallagher. “So, in that sense, even though black holes are extremely exotic, they’re quite simple in describing them.”

A black hole is an astronomical object that NASA describes as “a gravitational pull so strong that nothing, not even light, can escape it.”

Types of Black Holes

There are two main classes of black holes observed: stellar-mass black holes that can be dozens of times larger than the sun, and supermassive black holes that can equate to billions of solar masses. Gallagher points to escape velocity to understand the mechanics of a black hole.

“If you’re on the surface of the earth, and you go straight up, you have to go fast enough so that you can overcome the gravity from the earth, or escape speed,” says Gallagher.

Earth’s escape speed is 11 kilometers per second, meaning that a rocket needs to propel at least that fast to escape Earth’s gravity. Something more massive, like the sun, requires a greater speed of about 600 kilometers per second.

“If a planet is massive and dense enough, then the speed to escape is the speed of light. Once the escape speed becomes the speed of light, that means nothing can escape because nothing is faster than the speed of light,” says Gallagher.

In other words, a black hole requires that the escape speed be equal to or greater than the speed of sound, 300,000 kilometers per second. How a black hole would impact a person depends mainly on its size.

Smaller Black Holes and the Human Body

Robert Scherrer, a professor of physics at Vanderbilt University, suggested in a pre-print study last month that a hypothetical, early universe, small primordial black hole would feel like gunshot wound.

At first, Scherrer started looking into whether the gravitational force of a black hole could disassociate human cells but found that a shockwave passing through the body would be much more destructive and is “analogous to a gunshot wound.”

“And we know exactly what gunshot wounds do to the body,” says Scherrer. “Smaller black holes cause gravitational forces to be localized over a much smaller area, so if one were to pass through a person, it would exert force on their cells.” Scherrer adds that the impact of a primordial black hole would also cause a shockwave.

“A shockwave comes from any high-velocity object passing through your body, it sends out a sonic wave if it’s going faster than the speed of sound,” says Scherrer.

Both a bullet and a primordial black hole would emit a shockwave upon impact to act in similar ways but at very different speeds. According to Scherrer’s calculations, a black hole would travel at about 125 miles per second – much faster than a bullet, which is measured in hundreds or thousands of feet per second.

Though there’s no evidence that primordial black holes exist, there’s also no way to prove they aren’t moving through the solar system without our knowledge.

“Luckily, primordial black holes are sufficiently rare, and you’re unlikely to encounter either kind,” says Scherrer.

Larger Black Holes and Spaghettification

Much larger supermassive and stellar black holes – both of which are known to exist – would destroy a human through their gravitational pull, or tidal force.

“The force of gravity is not uniform, rather, it decays with distance,” says Scherrer, adding that as a person gets closer to the black hole, these extreme tidal forces would pull them apart.

If a person were to lie down with their feet closest to the black hole, the stronger gravitational pull would “rip” them apart, pulling harder at the feet than at the head. This is known as spaghettification, a gravitational force that acts on the entire body to stretch a person “infinitely long and infinitely thin,” says Scherrer.

Hawking Radiation

Hawking radiation is a theoretical phenomenon that suggests black holes emit thermal radiation, leading to their gradual evaporation over time. This radiation could also harm a human who comes into too close contact with a black hole.

Avi Loeb, a professor of science and founding director of Harvard’s Black Hole Initiative, explains hawking radiation as a lightbulb that creates its own energy before evaporating into a fireball.

And that’s exactly how radiation from a black hole could kill you. Radiation from a larger primordial black hole would feel like a body being torn apart, says Loeb.

“It’s a feeling that is similar to encountering a dark ghost, something that you can’t see but is inside you,” says Loeb.

A smaller black hole passing through a human would cause an experience more like a “giant fireball” that would feel like being burned from the inside out, says Loeb.

Should we be Concerned?

While theorizing the impacts a black hole would have on the human body is a thought-provoking experiment, experts agree there is no need to lose sleep.

“It’s not like we have to worry about a primordial black hole wiping out humanity,” says Gallagher.

The probability of being hit by a primordial black hole is negligible, says Loeb. Even if each of the 100 billion stars like our Sun hosted 8 billion human-like beings, only one would be killed by a primordial black hole every 20 years.

“Medical insurance companies can ignore these risks, even if they were to open branches on all the habitable planets to serve the entire Milky Way Galaxy, they don’t need to worry about the primordial black holes killing human-like beings,” says Loeb.

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Madison’s reporting focuses on marine and environmental issues, climate change, and novel scientific discoveries related to health and technology. Raised on an island in southeast Alaska, Madison is now based in western Montana. Her writing has been featured in Time, Snopes, Business Insider, Mountain Journal, EcoWatch, and Alaska Magazine, among others. When not writing, Madison teaches yoga, raises chickens, and fosters adoptable dogs and cats.

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