26 November 2025
A bizarre-sounding but very real physics question is dominating space-news feeds this week: what would actually happen if a tiny primordial black hole shot straight through your body?
In a new peer‑reviewed paper in International Journal of Modern Physics D, Vanderbilt University physicist Robert J. Scherrer runs the numbers in detail. The headline result: unless the black hole is enormously massive (by human standards), the damage would range from “less than a bullet wound” to “nothing at all” – and the chances of such an encounter are essentially zero. [1]
Since late November 21, coverage of the study has spread from Phys.org and Vanderbilt University’s news site to ScienceAlert, IFLScience, EarthSky, Gizmodo and others, turning a niche cosmology calculation into one of today’s most-read space stories. [2]
Key takeaways
- The study asks a very specific question: What is the minimum mass a tiny primordial black hole must have to cause serious injury or death when passing through a human body? [3]
- Two mechanisms are considered:
- A supersonic shock wave ripping through tissue like a gunshot.
- Tidal gravitational forces that could pull cells – especially brain cells – apart. [4]
- For serious “bullet‑like” injury, the black hole must weigh at least about 1.4 × 10¹⁷ grams, roughly 140 billion metric tons, comparable to a sizeable asteroid. [5]
- At those masses, the black hole’s diameter is still smaller than an atom – about 0.4 picometers, hundreds of times smaller than a hydrogen atom. [6]
- Tidal forces in the brain become competitive only for even larger masses of around 7 × 10¹⁸–7 × 10¹⁹ grams (roughly 7–70 trillion tons), similar to the asteroid Iris. [7]
- Even if all dark matter were made of such black holes, the expected rate of human injuries is about 10⁻¹⁸ per year – equivalent to one accident in a quintillion years, vastly longer than the universe has existed. [8]
- Because we don’t see people mysteriously dying from invisible cosmic bullets, the work helps tighten constraints on primordial black holes as dark‑matter candidates. [9]
From sci‑fi nightmare to serious physics
The question sounds like something lifted straight from 1970s science fiction – and that’s no coincidence. Scherrer has said the project was partly inspired by a story he read decades ago in which someone dies after a tiny black hole passes through them. [10]
But the study isn’t just an exercise in morbid imagination. It’s part of a larger scientific effort to pin down the nature of dark matter, the invisible stuff that appears to make up about 27 percent of the universe’s mass‑energy budget. [11]
One long‑shot idea is that some or all dark matter could be made of primordial black holes – black holes that formed in the very early universe, within the first fractions of a second after the Big Bang, from extreme density fluctuations. [12]
Unlike the “normal” black holes born from dying stars, primordial black holes could span a huge range of masses, from far lighter than an asteroid to heavier than the Sun. Some models allow them to be much smaller than an atom, yet still incredibly dense. [13]
Scherrer’s logic is clever:
- Work out how destructive a passing primordial black hole of a given mass would be to a human.
- Ask whether we’ve ever observed such mysterious, unexplained injuries (we have not).
- Use that absence of horror stories to rule out certain combinations of mass and abundance for primordial black holes. [14]
This builds on his earlier work on MACROs – hypothetical “macroscopic” chunks of dark matter. In that study, he showed that if MACROs were abundant enough, they’d have left a trail of catastrophic human injuries by now, so their properties must be tightly limited. [15]
What exactly is a primordial black hole?
Primordial black holes (PBHs) are hypothetical objects that might have formed before any stars existed, when the early universe was extremely hot and dense. In some models, local regions became so dense that they collapsed directly into black holes. [16]
Phys.org and EarthSky summarize the currently allowed mass range like this:
- At the low end, PBHs could be 100,000 times lighter than a paperclip.
- At the high end, they could be up to 100,000 times more massive than the Sun. [17]
Because they don’t emit light, we’ve never definitively detected one. But they remain intriguing dark‑matter candidates, especially in certain mass ranges where other particle‑physics explanations struggle. [18]
That’s where Scherrer’s “what if one hits a person?” calculation comes in: if PBHs were both common and dangerous, our species’ continued existence would already have ruled them out.
Two ways a tiny black hole could hurt you
In the new paper – initially posted on arXiv in February 2025 and now published in International Journal of Modern Physics D – Scherrer zooms in on two specific effects produced by a fast‑moving PBH: [19]
- Supersonic shock waves
- Tidal gravitational forces
1. Supersonic shock waves: the cosmic bullet
Primordial black holes zooming through our galaxy would typically move at hundreds of kilometers per second – much faster than the speed of sound in air or human tissue. [20]
When any object travels faster than sound through a medium, it creates a shock wave: a cone of compressed material radiating outwards from its path. In the human body, this is exactly what happens when a bullet passes through tissue.
Scherrer calculates that a PBH with a mass of around 100 billion tons would create a shock wave less damaging than a small‑caliber (.22) bullet. [21]
To reach the threshold where this shock wave could cause serious injury or death, the PBH must be heavier – above about 1.4 × 10¹⁷ grams, or 140 billion metric tons. That’s roughly seven times the mass of the asteroid 4179 Toutatis. [22]
And yet, at that mass the black hole’s Schwarzschild diameter is only about 0.4 picometers – hundreds of times smaller than a hydrogen atom (diameter ~106 picometers). [23]
So from your perspective, the encounter would look and feel nothing like being swallowed by a giant cosmic vortex. It would be more like being hit by an invisible ultra‑relativistic BB pellet that punches a neat, destructive channel through your body and exits on the other side.
2. Tidal forces: microscopic spaghettification
The second effect is more exotic. Black holes create extreme tidal forces: differences in gravitational pull between two nearby points. In extreme cases, these forces can stretch objects into long strands – a process often nicknamed “spaghettification.” [24]
Inside a human body, tidal forces might tear individual cells apart, especially delicate brain cells, which are among the most sensitive structures we have. [25]
When Scherrer crunches the numbers, he finds:
- To exert tidal forces strong enough to rip apart brain cells, a PBH needs a mass of at least about 7 × 10¹⁸ grams, and potentially up to 7 × 10¹⁹ grams. That’s roughly 7–70 trillion metric tons – again comparable to a substantial asteroid, such as 7 Iris. [26]
By the time a PBH is that massive, the shock wave effect is already catastrophic, so tidal tearing doesn’t add much to the overall lethality. In Scherrer’s words, the supersonic “bullet” is the dominant killer; gravity’s stretching effect is a secondary concern. [27]
How likely is it that a tiny black hole hits you?
Here’s the part that’s gone viral – and that should let you sleep tonight.
Using standard estimates for how many primordial black holes could exist in our galaxy without conflicting with other observations, Scherrer estimates that a PBH heavy enough to hurt someone would hit a human, somewhere in the universe, with a rate of about 10⁻¹⁸ events per year. [28]
That corresponds to one accident every 10¹⁸ years – a quintillion years. The universe is currently about 13.8 billion years old, so you’re talking tens of millions of times longer than the entire history of everything so far. [29]
Put differently:
- The odds that a lethal primordial black hole hits anyone alive today are effectively zero.
- Smaller PBHs, if they exist, would pass straight through you without you noticing, interacting so weakly that they leave no obvious trace. [30]
Several outlets – from EarthSky to Gizmodo – have emphasized the same bottom line: this is a fun thought experiment, not a new item for your list of real‑world fears. [31]
Why the result matters for dark matter
If primordial black holes were both:
- Common enough to account for a large fraction of dark matter, and
- Massive enough to be lethal when they hit people,
then by now we might expect to have seen mysterious, bullet‑like injuries with no conventional cause. We haven’t. [32]
Scherrer’s calculation translates that observation into quantitative limits on how many PBHs of a given mass can exist. Interestingly, the minimum lethal mass he finds sits right at the lower edge of one of the remaining viable mass windows for primordial‑black‑hole dark matter. [33]
That makes this study part of a broader 2025 trend: using increasingly creative methods – from gravitational‑wave detections to galaxy‑scale surveys – to hunt for or rule out primordial black holes as the long‑sought “missing mass” of the cosmos. [34]
How the story is playing out today (26 November 2025)
As of today, 26 November 2025, the black‑hole‑through‑your‑body study is still everywhere:
- ScienceAlert highlights how even a 100‑billion‑ton black hole would be less damaging than a .22‑caliber bullet, and stresses just how vanishingly rare a dangerous encounter would be. [35]
- IFLScience digs into the dark‑matter angle and notes that the lethal PBH mass range overlaps with the lower bound on PBH dark matter, making the lack of cosmic‑bullet victims a useful constraint. [36]
- Phys.org and EarthSky focus on the underlying Vanderbilt press release, explaining in accessible terms how shock waves and tidal forces would work inside the human body. [37]
- Universe Space Tech (Universe Magazine) and other international outlets have translated and localized the story, underscoring that a PBH big enough to hurt you would be more massive than some famous asteroids yet still smaller than an atom. [38]
- Popular‑science sites like Gizmodo have joined in mainly to reassure readers: you definitely do not need to start worrying about invisible black holes sniping at you from deep space. [39]
Taken together, today’s coverage paints a consistent picture:
Primordial black holes are an intriguing, still‑unproven idea that might help explain dark matter – but they are not a realistic threat to human life.
References
1. phys.org, 2. phys.org, 3. arxiv.org, 4. phys.org, 5. arxiv.org, 6. www.sciencealert.com, 7. www.iflscience.com, 8. www.iflscience.com, 9. arxiv.org, 10. phys.org, 11. www.iflscience.com, 12. phys.org, 13. earthsky.org, 14. phys.org, 15. phys.org, 16. phys.org, 17. phys.org, 18. www.space.com, 19. arxiv.org, 20. www.sciencealert.com, 21. www.sciencealert.com, 22. arxiv.org, 23. www.sciencealert.com, 24. www.sciencealert.com, 25. www.iflscience.com, 26. www.iflscience.com, 27. arxiv.org, 28. arxiv.org, 29. arxiv.org, 30. www.sciencealert.com, 31. earthsky.org, 32. phys.org, 33. www.iflscience.com, 34. earthsky.org, 35. www.sciencealert.com, 36. www.iflscience.com, 37. phys.org, 38. universemagazine.com, 39. gizmodo.com
