Excess antimatter does not originate from nearby pulsars, study reports

Astronomers have managed to cross off one potential source for antimatter.
By Ian Marsh | Nov 20, 2017
Researchers working at a mountaintop observatory in central Mexico may have shed light on the origins of antimatter.

Earth is constantly showered by high-energy particles that rain down from numerous cosmic sources. While scientists have identified and accounted for a variety of those sources over the years, the origin of some particles continue to elude experts.

In the new research, a team from various U.S. universities, expands on that research by potentially shedding light on positrons -- the antimatter complements of electrons.

Typically, high-energy particles like protons are able to create pairs of positrons and electrons when they interact with dust and gas in space. Researchers became intrigued by that process in 2008, when they found unusually high numbers -- 10 times what they expected to see -- of earthbound positrons.

The team in the recent study analyzed that phenomenon and came up with a two different explanations for the excess particles. One hypothesis suggests that they come from nearby pulsars -- rapidly spinning cores of burnt-out stars-- while another states they may originate in the mysterious substance known as dark matter.

To look at both ideas, the astronomers used the High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory to take detailed measurements of the gamma-rays coming from the directions of the nearby pulsars Geminga and its companion PSR B0656+14. This revealed that particles from the pulsars stream too slow to account for any excess positrons. As a result, to make it to Earth the particles would have needed to leave before the pulsars formed.

"The most remarkable thing that we could highlight here is that for the first time we've performed a measurement and calculation of the positron flux, and got the opposite of what most people thought." Rubn Lpez-Coto from the National Institute of Nuclear Physics in Italy told Gizmodo.

While this does not prove where the particles come from, it does take away one compelling theory from the list. Narrowing the options is important because it helps scientists learn more about the universe as a whole.

Though dark matter is the next compelling source for the particles, there are many other astrophysical processes that need to be taken into account as well. For instance, supernova remnants and bright objects known as microquasars can also produce positrons. The team plans to look at such phenomena next.

"Our measurement doesn't decide the question in favor of dark matter, but any new theory that attempts to explain the excess using pulsars will need to match the new data," said lead investigator Jordan Goodman, a physicist at the University of Maryland, according toSpace.com

The newstudyis published in the journalScience.

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