Where did the ‘Oh-My-God’ particle come from?

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April 3, 2026

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Where did the ‘Oh-My-God’ particle come from?

A single subatomic particle from deep space had the same energy as a baseball pitch, and scientists still don’t know how it got here

By Phil Plait edited by Lee Billings

fotograzia/Getty Images

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Our planet is under a constant bombardment of radiation—from space.

Well, maybe it’s not as scary as that makes it seem. “Radiation” is a catchall term astronomers use for forms of light—including visible light, the kind we see—and also for subatomic particles sleeting through space. We don’t normally think of such particles as “rays”—cosmic rays, to be precise—but we still use that nomenclature because of lingo inertia.

Some cosmic rays come from the sun, some from elsewhere in our Milky Way, and others, called extragalactic cosmic rays, trace their origins across vast distances to other galaxies.

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That’s a remarkable thought, actually: Earth gets hit routinely by particles from other galaxies. That’s a long hike—a journey of tens of millions of light-years, sometimes more, ending when one of these wayward rays is absorbed harmlessly by our atmosphere, high above our heads.

These particles come in with a broad range of velocities, which in turn gives them a broad range of kinetic energy, the energy of motion. In our macroscopic universe, we use a unit such as joules to measure energy, which is still rather small. (It takes about four joules to raise a cubic centimeter of water 1 degree Celsius.) Particle physicists, however, use a far smaller unit called an electron volt (or eV). It takes 26 million trillion of them to heat that same amount of water! That’s a more appropriate unit for particles, most of the time. But cosmic rays are moving so rapidly—near the speed of light—that they can have a very high kinetic energy, easily reaching the mega electron volt (MeV) and giga electron volt (GeV) level.

You still wouldn’t feel it if one of these struck you. But shockingly, some cosmic rays have far, far higher energies than this.

In 1991 the Fly’s Eye detector, which monitored the sky for the glow caused by energetic particles slamming into our atmosphere, detected a flash so huge it defied belief: the cosmic ray that sparked it had an energy of 320 quintillion eV, or 320 billion GeV. That’s millions of times the kinetic energy of protons we can spin up in our most powerful particle accelerators. It’s so energetic, in fact, that it actually has a decent macroscopic equivalent: this cosmic ray carried 51 joules of kinetic energy, which is about the same as a slow curveball—but this energy came from a single subatomic particle.

It’s been nicknamed the “Oh-My-God” particle, and it makes the hair on the back of my neck stand up.

Why? Because protons are almost incomprehensibly small—as an analogy, the size of a proton compared to the size of an orange is roughly the same as the size of an orange compared to the diameter of Neptune’s orbit around the sun.

The OMG particle is a big mystery. For one thing, to have that much energy, it must have been traveling incredibly fast relative to Earth. Assuming it was a proton, it was moving at a speed of 99.9999999999999999999995 percent the speed of light. If a photon and the OMG particle had been in a race since the universe first formed, the particle now would only be about 600 meters behind.

So what could kick a particle like this up to such ridiculously high speeds? The answer may shock you.

That’s not clickbait: shock waves, specifically in catastrophically high-energy structures such as the focused beams of matter and energy pouring forth from a supermassive black hole. Ionized gas moving rapidly outward from such events carries along extremely strong magnetic fields. Charged subatomic particles (such as protons, which carry a positive electrical charge) are accelerated when moving through such fields, sometimes to high speed. But if the gas collides with other gas clouds, the subatomic particles can ping-pong between them, gaining energy every time they bounce