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As a SciShow viewer, you can keep building your STEM skills with a 30 day free trial and 20% off an annual premium subscription at Brilliant.org/SciShow. On October 15th, 1991, in the starry night sky above Utah, an object from deep space struck the atmosphere.   This unidentified falling  object wasn’t a spaceship.

Nor was it a meteor or asteroid. It was a single subatomic particle… with enough energy to mimic dropping a bowling ball on your foot. Astronomers dubbed it the Oh-My-God particle, and as we’re filming this episode, it still holds the record for the most energy ever detected  in a single particle.

And after three decades of research, astronomers still don’t know exactly what the Oh My God Particle was, or where the frick it came from. [intro] The Oh-My-God Particle belongs to a more general  category of massive particles, that’s particles with mass. zooming quickly through outer space. They’re called cosmic rays, and they hit the Earth’s atmosphere all the time, with a wide range of energies. And every year, astronomers pick up roughly two that have energies similar  to the Oh-My-God Particle.

They’re called extreme-energy cosmic rays, or EECRs and they all seem to break a pretty  well-established law of physics. . Einstein’s special theory of relativity tells us the universe has a sort of cosmic speed limit, equivalent to how fast light  travels through a vacuum. It also tells us why nothing with mass can ever reach that speed limit.

For every extra bit of energy you pump into a particle to make it go faster, the less and less of a speed boost you get. Lightspeed will always be out of reach, even for something as light as a proton. But thanks to fancy, sophisticated technology like the Large Hadron Collider, physicists on Earth can accelerate particles to about 99.999 9991% of the speed of light That’s pretty darn fast.

But if the Oh-My-God Particle really was a single proton, then it was traveling at ninety-nine point nine… and then twenty more nines… 51 percent the speed of light. It’s not 100%, so the laws of physics are working exactly as they should so far. But regardless of how much energy a cosmic ray particle gets, it shouldn’t be able to keep it.

Because even in the deepest  darkest corners of space, there’s still a sea of particles  it has to slog through, whether it’s the occasional hydrogen ion, or the light left over from the Big Bang that is literally everywhere. So as a cosmic ray travels through the deep space between galaxies, it’s basically guaranteed to bump into something and lose some of its energy in the process. In the 1960s, three scientists worked out that these statistically inevitable collisions impose a limit on how much energy a cosmic ray can maintain.

It has a name, it’s known as the GZK limit, taking the first letter from each guy’s last name, and that’s where the Oh-My-God Particle, and other EECRs, appear to break the law. They all have energies above the GZK limit. So what gives?

Do we have to time travel back to the 60s and slap some chalk out of theoretician hands? Well, maybe. The limit could be wrong.

After all, it’s a model of a rather complicated field of physics. But at the very least, the GZK limit does explain more general observations of cosmic ray energies. Astronomers do see fewer EECRs than they’d they would expect  without the rule in place.

So instead, maybe the thing pumping out these particles is too close, cosmologically speaking, for the GZK limit to kick into effect. Instead of traversing several  hundred million light years, the Oh-My-God particle may have started off in a neighboring galaxy… …and then the first substantial thing it lost energy to was us. It’s a sensible hypothesis, but astronomers have a major hurdle.

They don’t actually know what sources in the sky are making EECRs in the first place, let alone if one of them is nearby. Whatever phenomenon is out  there pumping out EECRs, physicists have already given  it a name: the Zevatron. And a Zevatron is probably something that creates a massive shockwave in the plasma around it, while also spitting out a bunch of  super speedy subatomic particles.

Basically, if those particles are  traveling fast to begin with, they can bounce back and forth between their source and the shockwave. And with each bounce they’ll  get a boost of energy. Eventually, some will get so much energy they break free of the whole shebang, and fly into space as an extreme-energy cosmic ray.

But what kind of astrophysical object could these Zevatrons be? Based on where some EECR  hotspots appear in the sky, and assuming cosmic rays travel  in roughly straight lines from their source to the Earth, whole galactic cores may be responsible. About one in every 1000 galaxies have centers known as Active Galactic Nuclei, where their supermassive black holes are actively gobbling up matter and spewing out a bunch of radiation… and yes, plasma shockwaves, that could be perfect for  making Oh-My-God-like particles.

And lucky for us, a couple  of these active galaxies don’t just align with these hotspots, they’re close enough to us that their EECRs could skirt the GZK limit. But don’t put your party shirt on, just yet. There are a few wrinkles that need to be ironed out.

One is that in October 2022, astronomers announced that they had detected an EECR with about 75% of the Oh-My-God Particle’s energy… that didn’t come from any hotspot. It’s basically… just out in the middle of nowhere! Another wrinkle is that one of our potential Zevatron galaxies has become less of a candidate over time, as fewer EECRs are getting spotted in that particular part of the sky.

But here’s the thing: Astronomers can’t actually assume all cosmic rays travel in mostly straight lines. Stray magnetic fields can deflect them as they travel through space. So just because an EECR looks like it came from the middle of nowhere, doesn’t mean it did.

That makes it even harder to  know where EECRs come from, but with enough data, astronomers might be able to  pin down their true origins. We will never know where exactly the Oh-My-God particle came from. But one day, we may know the answer for its excessively energetic siblings.

And hey, maybe while we’re  all waiting for that day, one of those siblings takes over the title of the most energetic particle ever detected. Then, we can all critique the name that scientists try to give that. And if you think you’ve got a better name already, feel free to leave it in the comments below.

Cause we all know that if  this happened to today…   it’s a good chance we would have called it the WTF particle … If the OMG particle is breaking  the universe’s speed limit, then maybe other limits could  be busted through as well. Like when it comes to how much you can learn, the classroom isn’t the limit! That’s where this video’s  sponsor, Brilliant comes in.

Brilliant is an online learning platform with thousands of interactive lessons in science, computer science, and math. Like their course on Astrophysics! This course is perfect for anyone  watching this video and thinking “You know, Active Galactic Nuclei” are just  a touch outside of my frame of reference.

You can just log into this Brilliant course and get a pretty introductory view  of astrophysics to cover some bases. And once you’ve caught the physics bug, you can go on to take the  Gravitational Physics course too! On Brilliant, there’s always more to learn.

And you can try it for free for 30 days at Brilliant.org/SciShow or by clicking the link in  the description down below. That link also gives you 20% off an annual premium Brilliant subscription. Thanks to Brilliant for  supporting this SciShow video and thanks to you for watching! [ OUTRO ]