OMG! Happy birthday, you super particle!
Way back in 1991, a tiny visitor from outer space arrived on Earth carrying a truly ridiculous amount of energy. 35 years later, scientists are still asking WTF?
OMFG!
At precisely 7:34 am GMT on 15 October 1991, something extraordinary happened in the skies above Utah, USA.
Here’s what we know.
A particle from outer space smashed into Earth’s atmosphere. It was travelling at almost the speed of light. It packed an unbelievable amount of energy into the incredibly small space it occupied. It may well have been a single proton. That’s not certain.
What is certain is this. We’d never seen anything like it before. And understanding exactly what it was could give us new insights into the very fundamental forces of the universe.
And the assembled geeks couldn’t believe the amount of energy we’re talking, get this!
From that day forward, it’s been known simply as the Oh-My-God particle.
35 years on, it’s fair to say we know a lot more about ultra-high-energy particles than we did in 1991. I mean, hey, we’re talking that brief window when Vanilla Ice was considered the future of rap.
But when it comes to the OG-OMG itself, you can only assume it’s somewhere in the cosmos snickering at how blissfully naive we remain about its story.
BPE — Big Particle Energy.
The numbers here are truly stunning.
The OMG particle carried an estimated 320 quintillion electronvolts of energy. That’s 320 followed by 18 zeros.
In everyday language, about 51 joules.
It’s cool. You can admit to me you have no idea how much energy that is. Don’t be self-conscious. I don’t either.
I know we measure dietary intake in kilojoules, so TBH 51 joules doesn’t sound massive.
But it turns out it’s roughly the kinetic energy of a cricket ball travelling at 100 kilometres an hour.
Okay. Now I’m impressed.
Because a cricket ball is a hell of a lot bigger than a subatomic particle. A cricket ball contains something like 10²⁶ protons and neutrons.
Look at it this way. If a proton was the size of a person, a cricket ball would extend out beyond Pluto’s orbit.
When I think of the energy this way, I start to say OMG — I’m even leaning towards FMD.
Another way of looking at it.
CERN’s Large Hadron Collider, the most powerful particle accelerator humans have ever built, can accelerate a proton to an energy of 7 trillion electronvolts.
The OMG particle packed 46 million times as much.
And the particle was travelling so extraordinarily close to the speed of light that, assuming it was a proton, a beam of light racing alongside it would take around 245,000 years to pull just one centimetre ahead.
Fly’s Eye in the Sky.
As is so often the case with these cutting-edge observations from the world of physics, no one actually observed the particle itself.
The dynamic detective in this case was a structure called Fly’s Eye, operating where else but at a military testing ground in Utah.
And when I say detection, it didn’t detect the particle itself, but the physical wreckage created by its collision with our atmosphere.
The impact triggered a spectacular cascade of secondary particles, known as an air shower.
These excited nitrogen molecules in the atmosphere, producing faint flashes of ultraviolet light.
And it was Fly’s Eye’s capturing of that ultraviolet light that allowed researchers to reconstruct the original particle’s energy and the direction from whence it came.
“We were hoping we might pick up something really unusual.” — David Kieda, then an assistant professor of physics and astronomy at the University of Utah and one of the Fly’s Eye scientists.
Don’t worry, Davey boy. You nailed the unusual bit.
Fly’s Eye ran until 1993 and was a comparatively small project. But it will always be able to say to its grandkids:
“Ha! I detected the OMG particle!”
So where the hell did it come from?
If you think the sheer levels of energy are the confusing bit here, well there’s a cherry on top. Where the Oh My God particle came from is even more baffling.
You see, scientists know of some pretty ferocious cosmic particle accelerators. You’ve got exploding stars, active galaxies and the environments surrounding supermassive black holes.
But while these galactic guns can really help fire a particle at incredible speeds, there’s a catch.
The universe is filled with leftover radiation from the Big Bang, known as the cosmic microwave background. Over immense distances, interactions with that radiation should drain energy from particles travelling at these extraordinary speeds.
So something launched this monster. But what? How close to Earth did it happen? And how did it reach us with still so much energy intact?
In 2021, another extraordinarily energetic particle arrived, carrying 244 quintillion electronvolts, about 3/4 of the punch OMG packed. Researchers named it Amaterasu, after the Japanese sun goddess.
But here’s the kicker. Scientists traced its arrival direction back towards a region of space known as the Local Void. A place with precious little going on, let alone anything capable of firing a particle with this much energy.
And just like the OMG particle, nobody could identify the cosmic powerhouse responsible.
“That’s the mystery of this — what the heck is going on?” — John Matthews, University of Utah .
Today, vast detector arrays in Argentina and Utah continue searching the skies.
For 35 years our best and brightest have been perplexed by perhaps the universe’s most spectacular subatomic bullet. Despite all that, we still don’t know who pulled the trigger.
Bring on the next 35 years of cosmological querying.
Further reading:
Scientific research:
• Bird et al. (1995), Detection of a Cosmic Ray with Measured Energy Well Beyond the Expected Spectral Cutoff Due to Cosmic Microwave Radiation. The Astrophysical Journal.
• Telescope Array Collaboration (2023), An Extremely Energetic Cosmic Ray Observed by a Surface Detector Array. Science.
General reporting:
• University of Utah — Why Scientists Haven’t Solved the Mystery of the OMG Particle.
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