Antiproton count hints at dark matter annihilation

New analyses of data from Space Station’s AMS experiment show signs of elusive cosmic mass

AMS experiment

ANTIPROTON ODDITY Two teams of researchers report possible signs of dark matter in data from the AMS experiment on the International Space Station (shown). Some of the antiprotons detected by AMS could have come from dark matter particles annihilating one another in space.


Whiffs of dark matter may be blowing in on a cosmic ray breeze. Antiprotons streaming down on Earth from space could be hinting at the existence of the invisible substance, two teams of researchers suggest.

Particles known as cosmic rays are constantly whizzing through space. These particles include protons and their antimatter partners, antiprotons. While antiprotons are produced in run-of-the-mill processes like particle collisions, additional ones could theoretically be birthed when dark matter particles annihilate one another.

In two papers in the May 12 Physical Review Letters, the two teams — one from Germany; the other from China and Taiwan — analyzed antiprotons detected by the Alpha Magnetic Spectrometer, located on the International Space Station. When dark matter’s contribution was included in predictions of the numbers of antiprotons expected, the calculations better matched the data, hinting that some of the antiprotons might come from dark matter annihilation.

The results agree with another potential glimmer of dark matter: a glut of high-energy radiation, known as gamma rays, seen in the center of the Milky Way. “That could just be a coincidence,” says theoretical astrophysicist Dan Hooper of Fermilab in Batavia, Ill., who was not involved with the new analyses. But “it does look pretty encouraging to me for that reason.” Other physicists, however, have recently questioned the gamma rays’ link to dark matter (SN Online: 4/24/17).

AMS previously spotted another potential dark matter hint: an overabundance of positrons, or antimatter electrons (SN: 5/4/13, p. 14). But some physicists believe that excess can be explained by more mundane sources, like spinning stars called pulsars.

Physics writer Emily Conover has a Ph.D. in physics from the University of Chicago. She is a two-time winner of the D.C. Science Writers’ Association Newsbrief award.

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