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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!
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[ OUTRO ]