How tiny black holes would behave inside the sun, Earth – and us

Dead Planets Society is a podcast that takes outlandish ideas about how to tinker with the cosmos – from snapping the moon in half to causing a gravitational wave apocalypse – and subjects them to the laws of physics to see how they fare. Listen on Apple, Spotify or on our podcast page.

The early universe may have been littered with black holes smaller than an atom but as heavy as a mountain. If these primordial black holes do exist, they would solve several of the biggest problems in cosmology – and create endless opportunities for the Dead Planets Society to make mischief.

In this episode, our hosts Chelsea Whyte and Leah Crane are joined by black hole astronomer Allison Kirkpatrick at the University of Kansas as they explore what would happen if a primordial black hole was placed inside various objects, from the sun to Earth to the human body. The consequences aren’t quite as simple as one might expect.

For a really tiny black hole, placing it inside a star or planet wouldn’t have much of an effect – it would either pass straight through or stick around in the centre, depending on the mass of the object. But once they get a little bigger, perhaps the mass of Earth but the radius of a grape, things start to get interesting. Such a black hole would dramatically decrease the sun’s lifetime, or swallow up a planet from the inside out.

On the plus side, black holes in this size range could be used to reorganise the cosmos through their gravitational pull. A tiny black hole near the surface of the moon could stop its inexorable retreat from Earth, for example.

For a human being, standing several metres away from a tiny black hole would be reasonably safe, according to Kirkpatrick – but the closer you get, the more its gravity will affect whatever part of your body is closest, and if you get too close it will rip you apart. If you somehow managed to teleport the black hole inside your body, it would also not go well for you.

Kirkpatrick says under no circumstances should a primordial black hole be placed inside a human being, because of the havoc it would immediately wreak upon their body. The American Medical Association did not respond to a request for comment on the effects of a black hole on the human body.