The Search for the Mysterious Source of Earth’s Antimatter

Fagjun | Published 2017-12-03 23:13

Something out there is blasting Earth with antimatter particles. What exactly is this source, and why is it flooding our atmosphere with antimatter?

Where is the antimatter in our atmosphere from?



Way back in 2008, the cosmic ray research module Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) found that our atmosphere is flooded with positrons, a kind of antimatter. Antimatter is, in a nutshell, the opposite of normal matter. It’s composed of the antiparticle of ordinary matter particles, with antiparticles being the corresponding “partners” of ordinary particles. Ordinary particles and antiparticles have the same mass, but have opposite charges. When particles and antiparticles collide, they destroy each other and release photons that make up gamma rays.


Positrons are the positively charged antiparticle equivalent of negatively charged electrons. PAMELA found that there were ten times more positrons in the Earth’s atmosphere than the amount that current models predict. If scientists can find the source of these antimatter particles, they may be able to solve some of the biggest mysteries in the universe.

The Slow Flow from Pulsars

Pulsars may or may not be the ones blasting us with positrons.



Years of work led researchers to narrow things down to two possible explanations. According to one hypothesis, the positrons came from nearby pulsars, which are the rapidly-spinning remains of burnt-out stars. The other hypothesis, meanwhile, is that the positrons come from the decaying matter of dark matter, an as-yet theoretical substance that has only been detected because of its gravitational effects on normal matter.


University of Maryland physicist Jordan Goodman and his colleagues took data from the High-Altitude Water Cherenkov (HAWC) gamma-ray observatory and analyzed them to see how plausible the pulsars explanation was. The researchers found that the particles were flowing away from the pulsars at a rate that’s too slow to account for their presence in our atmosphere. These particles should have left the pulsars before the pulsars were even formed for them to have reached Earth by now.


There are physicists who still think that it’s possible for these pulsars to be the source of Earth’s antimatter. However, the researchers say that if these pulsars are ruled out as a possible source, we must consider other things such as “other pulsars, other types of cosmic accelerators such as microquasars and supernova remnants, or the annihilation or decay of dark matter particles”.

The Possibility of Dark Matter

What is dark matter capable of?



Goodman is now leaning more toward the possibility that dark matter is to blame for flooding our atmosphere with antimatter particles. No one has ever directly observed dark matter, just its effects. A type of particle called weakly interacting massive particles (WIMPS), which is associated with dark matter, is what interacts with normal matter. If these particles decay or get annihilated somehow, it’s possible that they could produce pairs of electrons and positrons.


However, scientists also caution against jumping to the dark matter conclusion too quickly. There are those who say that the other possibilities mentioned above, like other pulsars or cosmic accelerators, should all be ruled out first before we even consider dark matter. This is because of the fact that as of now, dark matter is difficult to directly observe. Thus, researchers are set to narrow down these options to come to more conclusive findings.

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