FromQuarkstoQuasars

Cosmic Rays Give up Hints about Dark Matter

Joshua FilmerOctober 5th 2014
Image Credit: NASA
Image Credit: NASA

The Alpha Magnetic Spectrometer (AMS) is a particle detector on board the International Space Station. One of it’s primary missions is to help scientists study dark matter. It has already analyzed 41-billion cosmic rays and, last year, helped scientists to learn more about this mysterious substance. The newest results from the AMS has increased our observations by 50% and have helped given us new insights into the nature of cosmic rays and dark matter.

Dark matter has, thus far, only been detected indirectly. We have yet to actually see any particles of dark matter, even though it out numbers visible matter 5 to 1 and makes up about 21% of the universe’s mass-energy (in contrast to visible matter’s tiny 4%). Dark mater is needed so the universe makes sense. Visible matter doesn’t create enough gravity to hold the universe together in the way we see. We’ve been able to detect dark matter’s influence and have been able to watch how it distorts light, thus giving credence to the idea that it’s actually there.

One of the most popular theories to describe dark matter proposes that it is nothing more than a weakly interacting massive particle (WIMPs). Every once in a while, two WIMPs collide and, when they do, scientists think the annihilation will result in the creation of an electron and it’s antimatter twin, a positron. Positrons and electrons are identical with the exception that the former has a positive charge and the latter has a negative one.

AMS is helping particle scientists study this. Cosmic rays are particles, mostly protons, positrons, and electrons. Scientists have found there is a huge imbalance between the number of electrons and positrons that they would expect to see. This imbalance, favoring the positron, shows that there must be some other process responsible for creating positrons, this is where dark mater comes in. The excess of positrons could be explained by dark matter collisions.

Image Credit: NASA
Image Credit: NASA

If the electrons and the positrons seen by AMS were created by the same event, there should be a one to one ratio and the energy levels should match (the energy of one electron should be the same as the energy of it’s positron partner). Samuel Ting, a scientists involved with the AMS project, called this discovery “very, very strange” and stated, “They have no relation to each other. We spent a lot of time checking this; there’s no question this is not correct.” The natural conclusion is the stream of electrons AMS detects are coming from a different source than the positrons it encounters.

For scientists to actually prove dark mater exists, they’d need to catch a particle of dark matter. So, this discovery is a long way from proving that this mysterious substance is actually there, but it really helps us fine tune our search and it may pave the way for the discovery of the universe’s missing matter.

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