spaceSpace and Physics

Earth Is Being Pummelled With Anti Matter Right Now, And We Have No Idea Why


Jonathan O'Callaghan

Senior Staff Writer

An image of the two pulsars. John Pretz

Scientists have discovered that nearby pulsars, neutron stars that spin incredibly quickly, are unlikely to be the source of antimatter reaching Earth.

The findings, published in the journal Science, come from scientists using the High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory in Mexico. They captured the first wide-angle view of gamma rays coming from two rapidly spinning stars.


The problem centers around things called positrons. These are the antimatter cousins of electrons, and in 2008 we spotted an unusually high number in orbit around Earth as the result of cosmic rays.

Two theories were suggested for the origin, one that they had come from pulsars. The other was that they might be the related to dark matter.

These particular pulsars were thought to be the source, called Geminga and PSR B0656+14, located 1,000 light-years away.

However, studying the stars, the scientists found that the positrons would have lost too much energy had these stars been the source, so that idea can be seemingly ruled out.


"This new measurement is tantalizing because it strongly disfavors the idea that these extra positrons are coming to Earth from two nearby pulsars," said Jordan Goodman, professor of physics at the University of Maryland and the lead investigator, in a statement.

The HAWC detector itself is pretty awesome. It’s at an elevation of 4,100 meters (13,500 feet), sitting on the edge of the Sierra Negra volcano. It’s comprised of 300 huge water tanks, which are used to track cascades of particles coming down from the atmosphere.

The HAWC detector. Jordan A. Goodman

In this case, incoming gamma rays from the pulsars smashed into particles in the atmosphere, producing a shower of particles that could be measured in the tanks by flashes of blue lights.

Measuring the energy from these particles, the researchers could then work out the number of positrons also associated with the pulsars. And the readings show there wasn’t enough energy to account for those seen at Earth.


Essentially, they found that matter wasn’t drifting away from the pulsars’ debris field fast enough to account for the positrons reaching Earth.

Quite what’s going on here, though, isn’t clear just yet. It does sort of point towards the dark matter idea, although this hasn’t been verified yet.

"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 account for what we've found," said Goodman.


spaceSpace and Physics
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  • 2008