Cosmic rays coming from space must have 'exotic' origin, scientists say

The unexpected flux of particles might be coming from unknown 'astrophysical sources', the authors suggest

Andrew Griffin
Thursday 16 November 2017 19:59
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An image of the HAWC detector consisting of 300 large (188,000 liter/50k gallon) water tanks, each with 4 photodetectors
An image of the HAWC detector consisting of 300 large (188,000 liter/50k gallon) water tanks, each with 4 photodetectors

Scientists have been left baffled by strange cosmic rays being sent from deep in space.

Numerous observations have found that Earth is being hit by far more positrons than would ever be expected. And it appears that previous explanations for that strange behaviour are wrong.

About 10 years ago, scientists first spotted a very high number of positrons in orbit a few hundred miles above Earth. Scientists then got to work trying to understand where they had come from.

The initial suggestion was that the particles were being thrown out by collapsed stars called pulsars. Others proposed the more mysterious explanation about dark matter.

But scientists have said that neither of those explanation appears to tally with the facts. And the positrons must have come from somewhere altogether more "exotic", they said.

They discovered that by looking at data taken from the High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory in Mexico. They measured two of the pulsars that were previously thought to be the origin of the excess positrons – and found that they are surrounded by a huge, murky crowd that stops most of the particles from escaping, according to the new research.

"This new measurement is tantalizing because it strongly disfavours the idea that these extra positrons are coming to Earth from two nearby pulsars, at least when you assume a relatively simple model for how positrons diffuse away from these spinning stars," said Jordan Goodman, professor of physics at the University of Maryland. "Our measurement doesn't decide the question in favour of dark matter, but any new theory that attempts to explain the excess using pulsars will need to account for what we've found."

The article concludes that the particles must be coming from some other unknown source – each of which will require a rethinking of their model of physics. One of the possibilities includes the "annihilation or decay of dark matter particles", as well as a range of other energetic, mysterious processes churning away deep in space.

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