A recent study delves into an intriguing question: what happens if a tiny black hole were to pass through a human body? Rather than leaving us disappointed with a bland “nothing much,” physicist Robert J. Scherrer aimed to pinpoint the minimum size of a black hole that could cause serious harm, or even death.
What Are Black Holes?
Black holes form when massive stars exhaust their fuel and collapse under their own gravity. This means that stellar black holes—those formed from stars—can’t be smaller than a certain size; they need a lot of mass packed into a tiny space. For most of us, falling into one is not a concern unless we’re larger than twenty solar masses! Instead, we might “turn into spaghetti” if we encountered one.
On the other hand, primordial black holes are theoretical; they may have emerged in the universe’s earliest moments when matter was densely packed. NASA suggests these could range from lighter than a paperclip to heavier than the Sun. Their existence remains unconfirmed, but some scientists believe smaller ones could pass through Earth harmlessly, while larger ones might make an appearance every thousand years.
Recent observations of black holes and gravitational waves have reignited interest in these cosmic phenomena. Scherrer noted that the collisions between larger black holes have sparked public fascination, creating a context ripe for exploration.
The Study’s Focus
Scherrer’s study builds on earlier work about Macroscopic Dark Matter (or MACRO). It found that if MACRO dark matter passed through a human body, the damage would be significant. Scherrer wondered if black holes might similarly impact humans and set out to find out.
He considered two primary effects:
- Shock Waves: As a primordial black hole moves, it would create a supersonic shock wave, damaging tissues along its path.
- Tidal Forces: These forces could disrupt cells, particularly the sensitive ones in our brains.
Calculating the energy needed to cause harm comparable to a bullet’s impact required a minimum black hole mass of about 1.4 × 10^17 grams, akin to an asteroid’s weight. For more severe damage, like that caused by tidal forces—essentially gravity’s pull on different cells—he found the necessary black hole mass to be around 7 × 10^18 to 7 × 10^19 grams.
In simple terms, while small primordial black holes might zip through us unnoticed, larger ones could mimic the effect of a gunshot, inflicting serious injury. Interestingly, the smallest black hole capable of causing significant harm aligns with the lower limit for these black holes as dark matter candidates.
Despite these findings, Scherrer reassured that even if primordial black holes exist, they’re unlikely to pose a danger to people. Statistically, the likelihood of such an event occurring is nearly zero—around 10^-18 injuries per year.
As Scherrer summarized, “Primordial black holes could theoretically exist, but their density is so low that collisions with humans are almost impossible.” The feasibility of these cosmic oddities brings to light fascinating questions about our universe and the nature of dark matter.
For more insights into black holes and their mysteries, check out this comprehensive overview from NASA.
