Earth telescopes detect highest-energy cosmic rays ever observed, origin unknown

Our Universe is teeming with extreme objects that are often difficult to imagine, like supernova remnants, pulsars, and active galactic nuclei, to name a few.

They’re all capable of emitting charged particles and gamma rays with incredibly high energy levels that often exceed the those produced during nuclear fusion in stars by several orders of magnitude.

Adding to the mystery, scientists have now detected cosmic electrons and positrons with energies over 10 tera-electronvolts (TeV). To put that into perspective, it is 1000-billion times greater than that of visible light.

“We’ve uncovered data in a crucial and previously unexplored energy range,” says Werner Hofmann from the Max Planck Institute for Nuclear Physics in Heidelberg. “It’s likely to remain a benchmark for the coming years.”

This breakthrough comes from the H.E.S.S. collaboration in Namibia. For the past decade, five telescopes have been peering into space, focusing on cosmic radiation and especially gamma rays.

Decade of stargazing pays off

Imagine spending ten years looking up at the sky every night. That’s basically what these researchers have been doing.

Using the H.E.S.S. telescopes, they’ve been collecting data on cosmic rays. And finally, their patience paid off.

They’ve managed to measure the energy distribution of cosmic electrons and positrons up to tens of TeV with incredible precision. Basically, they hit the cosmic jackpot.

What are cosmic rays?

Cosmic rays are high-energy particles that zip through space and occasionally crash into Earth’s atmosphere.

Most of them are protons or atomic nuclei that have lost their electrons, and they’re traveling at speeds close to the speed of light.

They come from all sorts of wild cosmic events like exploding stars (supernovae), distant galaxies, and even our own sun during solar flares.

When these speedy particles slam into the Earth’s atmosphere, they collide with atoms and create a shower of secondary particles. Some of these secondary particles make it all the way down to the surface.

Scientists study cosmic rays to learn more about these extreme events in the universe and to understand the fundamental particles and forces at play.

It’s like getting messages from space that tell us about the most energetic happenings out there.

Tracing cosmic rays is difficult

Because they’re deflected by magnetic fields, it’s tough to trace charged cosmic rays back to their source.

Plus, as they travel, they lose energy interacting with light and magnetic fields. This energy loss is especially big for electrons and positrons above the TeV range.

So, if we detect these high-energy particles here on Earth, they probably didn’t come from too far away.

When the team analyzed their data, they noticed something interesting: there’s a noticeable kink in the energy spectrum around 1 TeV.

Below and above this point, the spectrum behaves differently. This sharp change suggests something funky is happening at that energy level.

Cosmic rays culprit is unknown

To figure out what’s going on, the scientists compared their observations with computer models.

They looked at potential sources like pulsars — those are highly magnetized, rotating neutron stars left over after a supernova explosion.

Some pulsars emit winds of charged particles, and the shock fronts from these winds could be giving particles a big energy boost.

“The measured electrons most likely originate from very few sources in the vicinity of our own solar system, up to a maximum of a few thousand light years away,” says Kathrin Egberts from the University of Potsdam. “Sources at different distances would wash out this kink considerably.”

Why should we care about pulsars?

Think of pulsars as cosmic lighthouses. They’re super-dense remnants of massive stars that exploded in supernovae. Even though they’re only about the size of a city, they can have more mass than our Sun.

They spin incredibly fast — some hundreds of times per second — and shoot out beams of electromagnetic radiation from their magnetic poles.

When these beams sweep past Earth, we detect them as pulses, hence the name “pulsar.”

But they’re not just cool to think about. Pulsars have extreme magnetic fields and rapid rotation, making them natural particle accelerators.

They can boost particles to energies way beyond what we can achieve on Earth. Studying them helps us understand physics under conditions we can’t replicate in labs.

The H.E.S.S. Collaboration

The High Energy Stereoscopic System (H.E.S.S.) in Namibia is a group of telescopes designed to detect very high-energy gamma rays from cosmic sources.

By observing the faint flashes of light produced when gamma rays interact with Earth’s atmosphere — called Cherenkov radiation — H.E.S.S. can figure out the properties of these energetic particles.

Over the last decade, H.E.S.S. has been a game-changer in high-energy astrophysics.

It’s given us insights into all sorts of cosmic phenomena, and now it’s helping us possibly pinpoint the sources of high-energy cosmic electrons and positrons.

What does all of this mean?

To sum it all up, scientists have found that some of the most energetic particles zipping through space — cosmic electrons and positrons with energies over 10 tera-electronvolts (TeV) — are likely coming from a nearby pulsar just a few thousand light-years away.

Using a decade’s worth of data from the H.E.S.S. telescopes in Namibia, they’ve observed a sharp kink in the energy spectrum around 1 TeV, which suggests these particles are originating from a powerful source relatively close to us.

By matching their observations with computer models, the researchers believe that a pulsar — a highly magnetized, spinning neutron star — could be accelerating these particles to such high energies.

This discovery shows us that even nearby, there’s still a lot of mysterious and energetic activity going on that we’re completely unaware of and can’t even begin to explain.

Future observations and more detailed models might help us nail down exactly which pulsar is sending these particles our way.

With better technology and more data, we might even discover other nearby sources contributing to the high-energy cosmic ray population. Stay tuned!

The full study was published in the journal Physical Review Letters.

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