The latest clues about dark matter come courtesy of a precision instrument strapped to the International Space Station hurtling some 250 miles above the Earth. And luckily for physicists, they’re just about what they expected.
The Alpha Magnetic Spectrometer aboard the space station (AMS-02) has been searching for dark matter by recording cosmic rays since 2011, the production of which, according to a number of theories, could be evidence of dark matter annihilating itself. Last week, two teams of physicists working independently of one another say they have found evidence in antiproton data that dark matter might be the weakly interacting massive particles (WIMPs) that some physicists have been predicting.
Protons and antiprotons are one hypothesized result of the collision of two WIMPs. Physicists can use the number of antiprotons that interact with AMS-02 to infer whether they were created by WIMP collisions. Essentially, they developed mathematical models to predict the number of antiprotons that AMS-02 would detect, one if WIMPs were colliding and another if they weren’t. If one model is closer to the data recorded by AMS-02, then it’s more likely to be correct.
The two teams used different statistical techniques to estimate the mass of the WIMPs, but their approach was similar. In their WIMP-collision modelß, they fine tuned the expected mass of the WIMPs until their modeled results fit the data seen by AMS-02. In one, they predicted a mass of 80 GeV, and in the other, they predicted a range of 20–80 GeV.
But wait, there’s more. Here’s Xaq Rzetelny, reporting for Ars Technica:
Another important characteristic of dark matter is its cross-section, or the likelihood of two dark matter particles colliding. That’s determined by a lot of factors, such as how closely packed dark matter particles are within a galaxy, as well as the speed they’re traveling. So learning the cross-section would help researchers model the effect that dark matter has on galaxies and on the Universe on larger scales. Cuoco et al. estimate a cross-section of about 3×10-26 cubic centimeters per second, while Cui et al. estimate a range between .2×10-26 and 5×10-26. Again, the two papers are in agreement.
The models both teams used also accurately predict the number of gamma rays originating from the center of the galaxy, which gives them additional validity. In other words, they didn’t just make up models to fit the data from AMS-02—they used gamma ray data as independent evidence that the model can do more than just correctly predict the number antiprotons AMS-02 detected.
Two groups of physicists agreeing on two different results doesn’t mean that they’ve discovered what dark matter is. But it’s definitely the start of something promising.