An enormous helium balloon floating about 24 miles above Antarctica has detected a mix of high-energy electrons so exotic that researchers say the particles must have been created by some fascinating process: They may have been formed when dark matter particles collided and annihilated each other, or else a surprisingly close astronomical object like a pulsar could be spitting the electrons at Earth. Researchers can't yet determine which answer is correct, but say the dark matter explanation is more exciting.

Dark matter is one of astrophysics' greatest enigmas. It is thought to be five times more common than visible matter, but there is no proof of what it is made of. The existence of dark matter has largely been inferred from its gravitational effects, such as the fact that most galaxies have enough mass to remain as well-defined objects despite having too little visible matter to account for the necessary gravity [National Geographic News].

If the research balloon did detect the signature of dark matter through the particles left over from collisions, it would be the closest researchers have ever gotten to seeing the mysterious stuff. The high-energy electrons detected during the balloon's 30 days aloft matched predictions of the kinds of particles that would be produced by the collision of theoretical dark matter particles, known as "Kaluza-Klein" particles.

The KK particles are predicted by multiple-dimension theories of the universe and have long-been a leading candidate as the substance of dark matter. The new discovery then, if confirmed, would provide evidence that the fabric of space-time has many "compact" dimensions beyond the four that humans perceive. "If the Kaluza–Klein annihilation explanation proves to be correct, this will necessitate a fuller investigation of such multidimensional spaces, with potentially important implications for our understanding of the Universe," the authors conclude [Wired News].

The other potential explanation discussed in the Nature article [subscription required] sounds almost mundane when compared to multidimensional intrigue, although it involves extraordinary astronomical objects. If the electrons are part of the cosmic rays emitted by a pulsar (the spinning remnant of a collapsed star) or a microquasar (the material that orbits a small black hole), that strange object would have to lie within 3,000 light years from Earth, researchers say, because high-energy electrons can't travel far through space before their energy decreases.

But the team has spent four years trying to fit the signal to such an object and has yet to find a good match [New Scientist].

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