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Black Hole Collisions

January 15, 2014

It’s dangerous out there. Earth is threatened by asteroids and comets, storms on the Sun, and exploding stars, among other things. Fortunately, though, a recent study has some good news about another celestial danger: If a black hole hit Earth, you probably wouldn’t even notice it.

A black hole’s gravity is so powerful that nothing can escape its grasp — not even light. Some black holes are as massive as stars, while far heavier ones occupy the centers of many galaxies, including our own.

These black holes are so rare that Earth will probably never encounter one. But it’s possible that huge numbers of tiny black holes were created just after the Big Bang. These “primordial” black holes are as heavy as asteroids, but they’re smaller than an atom. If they exist, they outnumber all other types of black holes put together.

Scientists recently modeled what would happen if one of them hit Earth. Surprisingly, the answer is not much. The black hole would zip through our planet in less than a minute, shaking the surface just as an earthquake would. But the quake would be so weak that you might not even feel it.

And the risk of a collision is small. In fact, even if primordial black holes account for all of the universe’s mysterious dark matter, which outweighs normal matter, one would hit Earth only once every few million years. So black holes of any kind rank far down the list of cosmic threats.

More about black holes tomorrow.


Script by Ken Croswell, Copyright 2013

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