Space station ‘s antimatter detector finds its first evidence of dark matter

NASA file

A fish-eye view of the International Space Station from July 2011 shows the $2 billion Alpha Magnetic Spectrometer (AMS) in the foreground. A Russian Progress cargo ship and a Soyuz crew capsule are docked on the left end of the station. The structure extending to the left of the AMS is a thermal radiator. Off to the right, the shuttle Atlantis is docked to the station's Tranquility module.

By Alan Boyle, Science Editor, NBC News

Scientists say a $2 billion antimatter-hunting experiment on the International Space Station has detected its first hints of dark matter, the mysterious stuff that makes up almost a quarter of the universe.

The evidence from the Alpha Magnetic Spectrometer, revealed Wednesday at Europe's CERN particle physics lab, is based on an excess in the cosmic production of anti-electrons, also known as positrons. The AMS research team can't yet rule out other explanations for the excess, but the fresh findings provide the best clues yet as to the nature of dark matter.

"Over the coming months, AMS will be able to tell us conclusively whether these positrons are a signal for dark matter, or whether they have some other origin," Samuel Ting, an astrophysicist at the Massachusetts Institute of Technology who leads the international AMS collaboration, said in a CERN news release.

The results are to be published in Physical Review Letters and will be discussed during a NASA news conference at 1:30 p.m. ET Wednesday.

Dark matter is so named because it hasn't been detected directly through electromagnetic emissions, but primarily through its gravitational effect. Precise measurements of the movements of galaxies and galaxy clusters, as well as studies of the big bang's afterglow, indicate that it accounts for 22.7 percent of the universe's content. Another mysterious factor known as dark energy makes up 72.8 percent, leaving just 4.5 percent for ordinary matter.

Scientists have theorized that ultra-high-energy collisions involving dark matter particles could produce more positrons than expected. The best places to detect such collisions are in huge underground experiments such as CERN's Large Hadron Collider or in outer space, where cosmic rays can be measured more easily than they are on Earth.

The Alpha Magnetic Spectrometer is the most sensitive cosmic-ray detector ever put into orbit. Researchers from 16 countries worked for well more than a decade to get AMS ready for the space station, but it literally took an act of Congress to get the extra money needed for the launch. The bus-sized device was brought up on the shuttle Endeavour and installed in 2011, during the shuttle fleet's second-last mission.

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Space station 's antimatter detector finds its first evidence of dark matter