Astrophysicists have detected the most energetic electrons ever recorded raining down on Earth. With trillions of times the energy of visible light, these cosmic rays seem to be coming from a powerful source relatively close to our solar system.
Earth is constantly being bombarded by cosmic radiation, most of it from our own Sun. But other sources, like quasars, supernovae and gamma ray bursts, can fire off particles at extremely high energies. And now, scientists have identified the highest energy electrons ever seen blasting in from space.
That energy is measured in electronvolts (eV), where 1 eV is the amount of kinetic energy a single electron gains when accelerated by one volt. Most electrons in cosmic rays have energies of a few hundred gigaelectronvolts (GeV). But the newly detected record-breakers have been measured up to an astounding 40 teraelectronvolts (TeV). That’s trillions of eV.
The discovery was made by a team analyzing 10 years’ worth of data gathered by the HESS Observatory in Namibia. This facility detects cosmic rays in an intriguing way – when they enter the Earth’s atmosphere, they collide with atoms and molecules in the air and trigger a shower of secondary particles. The specific makeup of the showers can reveal the identity of the original particle.
Charged electrons – and their antimatter counterparts, positrons – only make up about 1% of cosmic rays, so it’s hard to detect them among the background noise of other particles. For this new study, the researchers used new algorithms to filter them out of the HESS dataset more accurately. This revealed a never-before-seen range of higher energy cosmic ray electrons, all the way up to 40 TeV.
Unfortunately, tracing back the source of cosmic ray electrons is tricky. Their path to us is bent as they pass by and through magnetic fields out in the cosmos, so by the time they reach us, they essentially could have come from anywhere.
A direction may be off the cards, but astronomers can at least figure out how far they’ve traveled. The longer these energetic particles zip through space, the more energy they dissipate. From this, the team says that the majority of the electrons, boasting energies below 1 TeV, probably came from a range of distant objects.
But those at the higher end of the spectrum could not have traveled very far, to still possess that amount of energy. The team calculated that these electrons must have come from a source within a few thousand light-years of our solar system. In cosmic terms, that’s pretty damn close.
The most obvious candidate, the team says, is a pulsar – a type of neutron star that produces beams of electromagnetic radiation from its poles. Just one pulsar could be responsible, or it might be a few within that distance.
The research was published in the journal Physical Review Letters.
Sources: Max Planck Gesellschaft, CNRS