What happens if you’re hit by a primordial black hole?

In the early 2000s, I gave a public lecture called “Seven Ways a Black Hole Can Kill You.” Despite the rather macabre subject matter, it was actually a fun talk – real science disguised as an ironic series of cartoonish astrophysical antics. I covered the usual topics, including simply falling into a black hole and getting spaghettified or being too close to the gamma-ray burst emitted when a new black hole forms.

Now, however, I wish I had been hit by an asteroid-mass subatomic black hole moving at a million miles per hour and born in the first moments after the big bang – and been hit by the shockwave that followed as the black hole traces a narrow corridor through your body.

I mean, obviously that’s what would happen. At least this is the conclusion of research published in 2025 in the International Journal of Modern Physics D. This is a rather unusual topic for a professional article – the title is “Gravitational effects of a small primordial black hole passing through the human body” – but there are real scientific conclusions about black holes and even dark matter that can be drawn from the fact that, fortunately, we have never seen such a macabre event occur.

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In fact, because some people worry about such things, let’s start with some good news: The odds of such an event happening, let alone to you or anyone you know, are so (literally) astronomically long that they’re difficult to express in any meaningful way. I estimate the chance of you dying this way is about the same as the chance of simultaneously winning the lottery and being struck by both lightning and an asteroid in a shark attack while on a unicycle juggling aardvarks.

Are you feeling better? Okay, let’s take a closer look, but not Also much closer, because yeah, look what it’s about.

As I wrote in my March 27, 2026 column, The Universe, primordial black holes, or PBHs, could have emerged in the first infinitesimal seconds after the formation of the cosmos itself, when immense pressures and densities in the hot miasma could theoretically have compressed clumps of matter into volumes so small that the gravity of these clumps became enormous, triggering an uncontrollable collapse. There you have it, the primordial black holes!

There is no real lower limit to the mass of a PBH. But due to strange effects of quantum mechanics, very small black holes actually emit a type of radiation called Hawking radiation, which causes them to evaporate all at once. Any PBH with a mass less than about a billion tonnes would have now completely dissipated. Other theoretical considerations, such as the observable effects of these PBHs emitting radiation and subatomic particles as they evaporate, bring this limit closer to 100 billion tons.

It’s about the mass of a small rocky asteroid, about four or five kilometers across. An impact on Earth from an asteroid like this would be very serious, no enough as bad as the one that wiped out the non-avian dinosaurs 66 million years ago, but it’s still not exactly a fun day.

The strange thing – and probably completely counter to your intuition – is that a PBH with this mass hitting Earth wouldn’t be as devastating.

How is this possible? It’s a black hole. This should tear the planet apart, right?

The reality, however, is that it is very, very little black hole. A PBH with this mass would be much smaller than a hydrogen atom. Although a black hole’s gravity is intense – that’s its defining characteristic – the strength decreases rapidly with distance. From a kilometer away, you would barely feel it.

On the other hand, of a centimeter far away, this PBH’s gravity would be millions of times stronger than Earth’s, so it would do a decent job of attracting matter. However, he wouldn’t have much time to do so. Relative to Earth, the typical speed of a PBH would be several hundred kilometers per second, or about a million kilometers per hour. It would cross our planet cleanly in less than a minute.

The amount of matter it would accumulate during this time would not be large, but it would still strongly affect any material around it through gravity. Combined with the rapid movement of the PBH – traveling at hundreds of times the speed of sound across most of our planet – this would create a shock wave not unlike an earthquake. Research published in the Astrophysics Journal in 2012 indicates that a billion-ton mass PBH passing through the Earth would create a seismic event equivalent to approximately a magnitude 4.0 earthquake. You would feel it, but it wouldn’t be that destructive. A 100 billion ton PBH would of course be more powerful, but still would not be globally destructive.

But what would happen if we hit a human directly?

The 2025 paper concludes that the outcome would not be great. The author calculated the energy of the shock wave that would be deposited in a human body using physics similar to that of a bullet impact, which, while worrying to say the least, is not a bad assumption from a scientific point of view. The author found that the minimum mass for a PBH to produce “significant” injury was just over 100 billion tons, so exactly about the mass we are considering.

The authors also calculated the tidal force effect of such an event: the destruction caused by the rapid change in gravity over distance that could, in effect, tear cells or organs apart. Given the extremely short time it would take for the black hole to pass through a human body – about a microsecond – the damage caused by the tides would be minimal. It would take a mass about 100 times larger to destroy tissue to a biologically unhealthy level, even if it went straight through your brain. It’s a relief, I suppose.

The body tunnel left behind also wouldn’t be as directly damaging as one might think; The PBH would be so small and move so quickly that it would likely interact directly with only a small number of atoms in your body, leaving only a submicroscopic channel behind despite its intense gravity.

Such a collision would be extremely rare anyway. There is a hypothesis that PBHs may make up a percentage of dark matter, the mysterious matter we know exists that outnumbers normal matter by about 5 to 1 in the universe. It’s hard to say how credible this idea is, but we can use it to calculate how often we can expect a PBH to encounter a human. The researcher found that, as an upper limit, we can expect this to happen once a month. billions of billions of years. For a normal person, that means never.

Earth is of course a bigger target and, according to other research, a PBH of 100 billion tonnes is expected to pass through our planet once every billion years. This is an upper limit, mind you, so it would probably be less often, and it assumes that these little black holes exist – we still don’t know if they actually exist. And if PBHs represent a lower percentage of dark matter than is currently theorized, then the rates would be even lower.

I’m an astronomer and I think about black holes. plot, but in my daily life, I worry more about climate change, car accidents, and the possibility of slipping in the shower than I do about having a close encounter like PBH. But just to be safe, I’ll try not to use a unicycle while juggling aardvarks.