What if the most powerful particle collider in the universe is not a machine on Earth, like the LHC, but rather a product of a distant stellar explosion? A new study confirms that certain supernovae can indeed produce ultra-high-energy particles, a thousand times more powerful than those generated by our technology. However, this spectacular capability only lasts for a few months, rendering the phenomenon almost invisible.
Ultra-Powerful, Yet Discreet Cosmic Rays
For nearly a century, scientists have detected cosmic rays—particles primarily made up of protons that originate from the deep cosmos and regularly strike the Earth. Some of these cosmic rays reach astonishing energy levels, exceeding the petaelectronvolt (PeV) mark, which is equivalent to a million billion electron volts. In comparison, the Large Hadron Collider (LHC) at CERN peaks at only 0.01 PeV.
These extreme cosmic rays have long puzzled astrophysicists: Where do they come from? How can particles be accelerated to such speeds in the interstellar void?
Supernovae in the Spotlight
The idea that supernovae—the cataclysmic explosions marking the death of massive stars—could be the source of these cosmic rays is not new. These events indeed release colossal energy and are accompanied by powerful magnetic fields, two essential ingredients for particle acceleration.
However, until now, the remnants of supernovae observed in our galaxy had never shown cosmic rays of such intensity. This paradox cast doubt on the hypothesis.
A Secret Within the Gas Envelope
A new study set to be published in Astronomy & Astrophysics offers an unexpected answer: Yes, supernovae can indeed become “ PeVatrons ” (the term used for cosmic accelerators capable of reaching PeV energy levels)… but under very specific conditions.
The star that explodes must have lost a significant amount of mass before its end—at least twice the mass of the Sun—through stellar winds. Moreover, this expelled matter must not have dispersed too far; it needs to form a dense, compact shell around the star.
When the supernova occurs, the shockwave travels through this gas envelope, creating a super-powerful magnetic environment that propels particles into a true energetic rollercoaster. With each bounce, they gain speed, reaching extreme levels of energy before escaping into space.
An Invisible Phenomenon… or Almost
The problem is that this ultra-powerful phenomenon lasts only a few months. Afterward, the shockwave weakens, and the acceleration ceases. This explains why we have never observed a supernova actively producing PeV cosmic rays: It would require the supernova to explode at just the right moment and not too far from us, which is extremely rare.
In the meantime, scientists continue to piece together the puzzle by studying the traces left behind by these ancient natural colliders. Perhaps one day, the universe will provide us with a live PeVatron.