Black holes have such strong gravity that not even light can escape. They are very dense and have intense gravitational forces.
Scientists think primordial black holes (PBH) might make up some or all of the Universe’s dark matter. If there are enough PBHs, they could have various effects. Researchers have suggested that a PBH as small as 1015 grams could create a noticeable seismic disturbance on Earth.
Scientists have suggested that primordial black holes (PBHs) could gather inside planets and asteroids, hollowing out their cores. They also noted that a PBH passing through Earth’s material would leave a detectable microscopic tunnel and suggested that such a passage through the human body would not be fatal. This is the question being addressed here.
A new paper by Robert J. Scherrer from the Department of Physics and Astronomy at Vanderbilt University explored the gravitational effects of a PBH passing through the human body. The aim was to determine the minimum black hole size needed to cause significant injury and to see if the lack of such injuries can set any limits on PBH properties.
Scientists were inspired by earlier work on macroscopic dark matter (MACROs), which showed that MACROs could cause severe damage to the human body. The lack of observed impacts helps set limits on MACRO mass and cross-section. While it’s known that a microscopic black hole would harm the human body, there are no precise calculations. Most discussions on this topic appear in popular literature, with the first mention of a PBH’s effect on the human body found in a work of fiction.
Small black holes may be hiding in planets
The paper explores the biological effects of a PBH passing through the human body, including the shock wave it would create and the tidal forces that would tear apart human cells. It calculates the minimum mass needed to cause serious injury or death from each effect and examines whether such effects can set practical limits on PBH properties. While the minimum mass required to cause serious injury or death falls within the interesting asteroid mass range, the allowed PBH abundance in this range is too small to have any observable effects on the human population.
Two main effects are studied:
- Shock Wave: The primordial black hole (PBH) would create a supersonic shock wave as it moves through the body, destroying tissue. This shock wave is similar to the one produced by a bullet passing through the body, where tissue damage depends on the energy deposited.
- Tidal Forces: The tidal gravitational forces from the PBH tear apart cells, especially brain cells, as they move through the body.
As a primordial black hole (PBH) passes through the human body, it exerts strong tidal forces, creating a tensile force on nearby cells and potentially tearing them apart. Brain cells are the most sensitive to this dissociation. A force of 10 – 100 nanonewtons for a few microseconds would be enough to pull apart brain cells.
The brain can be surprisingly resilient to damage over small areas, so the entire brain must experience the tidal force to ensure sufficient destruction of brain tissue to produce a detectable effect.
Robert noted, “The shock wave effect is found to be the dominant factor in causing serious injury or death, with a cutoff mass for primordial black holes (PBHs) being around MPBH>1.4×1017g. The number of PBHs above this mass is too small to have any observable effects on the human population.”
Journal Reference:
- Robert J. Scherrer. Gravitational Effects of a Small Primordial Black Hole Passing Through the Human Body. arxiv. DOI: 10.48550/arXiv.2502.09734
Source: Tech Explorist
