A Whiff of Dark Matter on the ISS   
       
   April 15, 2013: In science fiction, finding antimatter on board your spaceship   
   is not good news. Usually, it means you're moments away from an explosion.   
       
   In real life, though, finding antimatter could lead to a Nobel Prize.   
       
   On April 3rd, researchers led by Nobel Laureate Samuel Ting of MIT announced   
   that the Alpha Magnetic Spectrometer, a particle detector operating onboard   
   the International Space Station since 2011, has counted more than 400,000   
   positrons, the antimatter equivalent of electrons.  There's no danger of an   
   explosion, but the discovery is sending shock waves through the scientific   
   community.   
       
   http://www.youtube.com/watch?v=54AxeJFlVgI   
       
   A new ScienceCast video explores the possibility that signs of dark matter   
   have been detected onboard the International Space Station. Play it"These data   
   show the existence of a new physical phenomenon," wrote Ting and colleagues in   
   an article published in the Physical Review Letters. "It could be a sign of   
   dark matter."   
       
   The Alpha Magnetic Spectrometer ("AMS" for short) was delivered to the ISS by   
   the space shuttle Endeavour on its final flight in May 2011. In its first 18   
   months of operations, from May 19, 2011 to December 10, 2012, the AMS analyzed   
   25 billion cosmic ray events. Of these, an unprecedented number were   
   unambiguously identified as positrons.   
       
   Cosmic rays are subatomic particles such as protons and helium nuclei   
   accelerated to near-light speed by supernova explosions and other violent   
   events in the cosmos. Researchers have long known that cosmic rays contain a   
   sprinkling of antimatter.  Italy's PAMELA satellite detected high-energy   
   positrons in 2009, and NASA's Fermi gamma-ray observatory confirmed the find   
   two years later.   
       
   But where do the positrons come from?  The Universe is almost completely   
   devoid of antimatter, so the positron fraction of cosmic ray electrons--as   
   much as 10%--is a little surprising.   
       
   One idea is dark matter. Astronomers know that the vast majority of the   
   material Universe is actually made of dark matter rather than ordinary matter.   
   They just don't know what dark matter is.  It exerts gravity, but emits no   
   light, which makes it devilishly difficult to study.   
       
   http://tinyurl.com/cfwlrme   
       
   The Alpha Magnetic Spectrometer mounted outside the International Space   
   Station. A leading theory holds that dark matter is made of a particle called   
   the neutralino. Collisions between neutralinos should produce a large number   
   of high-energy positrons, which the AMS should be able to detect with   
   unprecedented sensitivity.   
       
   "The accuracy of our measurements is 1%, which is excellent, and we have   
   statistics unmatched by any other spacecraft," says Ting.   
       
   "So far the evidence supports the hypothesis of dark matter. But," he   
   cautions," it does not rule out another possibility--pulsars."   
       
   Pulsars are strongly-magnetized neutron stars formed in the aftermath of   
   supernova explosions.  They can spin on their axes thousands of times a   
   second, flinging particles into space with fantastic energies that   
   accelerators on Earth can't match.  Among these particles are pairs of   
   electrons and positrons.   
       
   AMS can distinguish between pulsars and dark matter--but not yet.  "We need   
   more data at higher energies to decide which is the correct explanation," says   
   Ting.  "It is only a matter of time, perhaps months or a few years."   
       
   Built by scientists from 16 countries with support from the US Dept. of   
   Energy, the Alpha Magnetic Spectrometer will continue operating for the rest   
   of the life of the space station - at least until 2020. Between now and then,   
   the mystery of dark matter could be solved, once and for all.   
       
   Credits:   
       
   Author: Dr. Tony Phillips | Production editor: Dr. Tony Phillips | Credit:   
   Science@NASA   
       
   More information:   
       
   Alpha Magnetic Spectrometer -- home page   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.91   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)