What if a Coin-Sized Black Hole Showed Up?#

So, you’re wondering what would happen if a black hole the size of a coin suddenly popped up nearby? The super short answer? You’d probably die.

But the slightly longer answer is, well, it depends. What do you mean by “size”? Do you mean a black hole that has the mass of a coin, or one that’s as wide as a coin? These are two very different scenarios!

Defining “Size”: Mass vs. Diameter#

Let’s break down what happens in each case.

Scenario 1: Black Hole with the Mass of a Coin#

Imagine a US nickel, which weighs about 5 grams. Now, suppose magically this tiny bit of mass somehow got squished down into a black hole.

• Its Radius: This black hole would be unbelievably small. Its radius would be about 10 to the power of -30 meters.
• Size Comparison: To give you an idea how small that is, a hydrogen atom is way, way bigger, around 10 to the power of -11 meters. Think of it like this: the black hole is as small compared to an atom as an atom is compared to the Sun. That’s just incredibly, unimaginably tiny!
• Lifetime: A black hole this small wouldn’t stick around for long. It would have an unimaginably short life before it decays through something called Hawking radiation. It would radiate away all its little bit of mass in a blink – specifically, in about 10 to the power of -23 seconds.
• The Boom: When its 5 grams of mass is converted into energy, it would release a massive 450 terajoules of energy. This explosion would be roughly three times more powerful than the energy released by the atomic bombs dropped on Hiroshima and Nagasaki combined.

In this scenario? Yes, you definitely die. And you also lose the coin, if you were holding it.

Scenario 2: Black Hole with the Diameter of a Coin#

Now, let’s think about a black hole that’s actually as wide as a common coin, say, the diameter of a US nickel.

• Its Mass: If a black hole was this size across, it would be way, way more massive than just a coin. In fact, a black hole with the diameter of a nickel would be a bit more massive than the entire planet Earth.
• Surface Gravity: The gravity right at its surface? It would be a billion billion (that’s 1,000,000,000,000,000,000) times stronger than Earth’s gravity right now.
• Tidal Forces: The pull of gravity from such a dense object isn’t just strong; it’s uneven over short distances. These are called tidal forces. They’d be so incredibly powerful that they’d rip apart your individual cells. You’d be consumed by the black hole before your brain could even figure out what was happening.

Understanding Gravity Around Dense Objects:

Normally, gravity gets weaker the farther away you are from something. Its pull reaches across the whole universe, getting fainter with distance. Here on Earth, the distance from your head and your toes to the planet’s center is pretty much the same.

But if you were standing on a nickel-sized black hole? Your feet would be hundreds of times closer to its center than your head. This difference in distance means the gravitational force on your feet would be tens of thousands of times larger than the force on your head. This huge difference in pull would stretch you and rip you into a billion pieces.

The Black Hole Consuming the Earth:

It wouldn’t stop with just turning you into cosmic spaghetti. This black hole, now slightly more massive than Earth, becomes the new big boss gravity-wise in the Earth–Moon system. We’d call it the Earth–Moon–Black-Hole-of-Death system.

• You might think the black hole would just sink into the Earth’s core and eat it from the inside.
• But actually, the Earth itself would move towards the black hole, like it’s orbiting it. It would bob around, getting huge chunks of its mass eaten away with each pass. Which, honestly, sounds way creepier.
• As the Earth gets munched from the inside out, it wouldn’t just vanish. It would collapse into a scattered, hot disk of rock spinning tightly around the black hole.
• The black hole would grow, slowly doubling its mass by the time it’s finished its Earth snack.

Effects Beyond Earth:

• The Moon: The Moon’s nice, round orbit would get yanked into a highly elliptical (squashed oval) path.
• The Solar System: The effects on the whole Solar system would be “awesome” in the old-fashioned, Biblical sense – meaning, absolutely terrifying.
  • The black hole’s tidal forces would likely mess up the paths of near-Earth asteroids, maybe even parts of the main asteroid belt.
  • This would send rocks careening wildly through the Solar system.
  • Getting hit by space rocks (bombardment and impacts) might become a regular thing for the next few million years.
• Other Planets: The other planets in the Solar system would feel a little nudge, but they’d mostly stay in their usual orbits.
• The Black Hole’s New Home: The black hole, which used to be Earth, would then continue orbiting the Sun right where Earth used to be.

And yes, in this scenario too? You definitely die.

Behind the Scenes & Shout-Outs#

Just so you know, this deep dive into coin-sized black holes was made possible thanks to contributions from people on Patreon. Seriously, thank you all so much for supporting this!

The whole topic came from a question originally posted on the AskScience subreddit. A big shout-out goes to Matt [Caplin?], who gave a fantastic answer there and also worked with us on this video. You should totally check out his blog, Quarks and Coffee, if you like this kind of awesome science stuff!

If you want to chat about the video or the idea, we’ve even got our own subreddit now.

And hey, if you’re curious to learn more about black holes or their equally wild cousins, neutron stars, there are links you can follow (or click, if you’re watching the video).

Oh, and one last thing – the subtitles for this video were created by the great community over at Amara.org.