Back in the early 2000s I gave a public talk 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 a tongue-in-cheek 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 released when a new black hole is formed.
Now, though, I wish I had covered getting hit by a subatomic asteroid-mass black hole moving at a million kilometers per hour that was born in the first moments after the big bang—and being blasted by the ensuing shock wave as the black hole carves a narrow corridor through your body.
I mean, obviously that’s what would happen. At least, that’s the conclusion of research published in 2025 in the International Journal of Modern Physics D. It’s a rather unusual topic for a professional paper—the title is “Gravitational Effects of a Small Primordial Black Hole Passing through the Human Body”—but there are some actual scientific conclusions about black holes and even dark matter that can be drawn from the fact that, thankfully, we haven’t ever seen such a grisly event occur.
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In fact, because some people fret about such things, let’s start off with a bit of good news: the odds of such an event happening at all, let alone to you or someone you know, are so (literally) astronomically long that they’re hard to express in a meaningful way. I’d estimate the chance of you dying this way is about the same as simultaneously winning the lottery and getting struck by both lightning and an asteroid during a shark attack while on a unicycle juggling aardvarks.
Feel better? Okay, let’s take a closer—but not too much closer, because yikes—look at what this is all about.
As I wrote in my March 27, 2026, The Universe column, primordial black holes, or PBHs, could have emerged in the first few infinitesimally thin slices of a second after the cosmos itself formed, when immense pressures and densities in the hot miasma could theoretically have compressed clumps of matter into volumes so small that the gravity of those clumps became huge, initiating a runaway collapse. Voilà, primordial black holes!
There’s no real lower limit to the mass of a PBH. But because of bizarre quantum mechanical effects very tiny black holes actually emit a type of radiation called Hawking radiation, causing them to evaporate away mass as they do so. Any PBH less than about a billion metric tons in mass would have wholly dissipated by now. Other theoretical considerations, such as any observable effects of these PBHs emitting radiation and subatomic particles as they evaporate, puts that limit closer to 100 billion metric tons.
That’s roughly the mass of a smallish rocky asteroid, perhaps four or five kilometers in diameter. An Earth impact from an asteroid like that would be very bad—not quite as bad as the one that wiped out the nonavian dinosaurs 66 million years ago but still not a really fun day.
The weird thing—and likely completely counter to your intuition—is that a PBH with that mass hitting Earth wouldn’t be anywhere near that devastating.
How can that be? It’s a black hole. It should tear the planet apart, right?
The reality, though, is that it’s very, very small black hole. A PBH with that mass would be far smaller than a hydrogen atom. Although the gravity of a black hole is intense—that’s its defining characteristic—the force drops off rapidly with distance. From a kilometer away, you’d barely feel it.
On the other hand, from a centimeter away, the gravity of this PBH would be millions of times stronger than Earth’s, so it would do a decent job of drawing material in. It wouldn’t have much time to do it, however. Relative to Earth, a typical speed for a PBH would be several hundred kilometers per second, or roughly a million kilometers per hour. It would pass clean through our planet in less than a minute.
The amount of material it would accrete in that time wouldn’t be much, but it would still strongly gravitationally affect any material around it. Together with the rapid motion of the PBH—traveling at hundreds of times the speed of sound through the bulk of our planet—this would create a shock wave not too dissimilar from an earthquake. Research published in the Astrophysical Journal in 2012 indicates that a PBH with a mass of a billion metric tons passing through Earth would create a seismic event equivalent to roughly a magnitude 4.0 earthquake. You’d feel it, but it wouldn’t be all that destructive. A 100-billion-metric-ton PBH would be stronger, of course, but still not globally destructive.
But what would happen if one directly hit a human?
The 2025 paper comes to the conclusion that the result wouldn’t be great. The author calculated the shock wave’s energy that would be deposited in a human body by using physics similar to that of a bullet impact, which, though disquieting to say the least, is not a bad assumption from a scientific standpoint. The author found that the minimum mass for a PBH to produce “significant” injury was just more than 100 billion tons, so right around the mass we’re considering.
The authors also calculated the effect of the tidal force from such an event: the destruction wrought by the rapid change of 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 traverse a human body—roughly a microsecond—the tidal damage would be minimal. It would take a mass approximately 100 times larger to destroy tissues at a biologically unhealthy level, even if it passed right through your brain. That’s a relief, I guess.
The corporeal tunnel left behind would not be as directly damaging as you might think, either; the PBH would be so small and moving so rapidly that it would likely only directly interact with a small number of atoms in your body, leaving behind only a submicroscopic channel despite its intense gravity.
Such a collision would be extraordinarily rare, anyway. There is a hypothesis that PBHs could make up a percentage of dark matter, the mysterious material we know exists and outmatches normal matter by about 5 to 1 in the universe. It’s hard to say how credible an idea this 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 every billion billion years. To a normal person, that means never.
Earth is a bigger target, of course, and, according to the other research, a 100-billion-metric-ton PBH should pass through our planet once every billion years. That’s an upper limit, mind you, so it likely would be less often, and that’s assuming these wee black holes exist at all—we still don’t know whether they really do. And if PBHs make up a smaller percentage of dark matter than currently theorized, then the rates would be even lower.
I’m an astronomer, and I think about black holes a lot, 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 of the PBH kind. But just to be safe, I’ll try to stay off a unicycle while juggling aardvarks.
