In the quest to learn the nature of dark matter, today brings a bit of good news. NASA announced that the Alpha Magnetic Spectrometer (AMS) particle detector on board the International Space Station had detected cosmic rays that may have been sent our way by the self-destruction of dark matter particles.
In May 2011 the shuttle Endeavour ferried the Alpha Magnetic Spectrometer (AMS) to the space station. The device uses a powerful magnet cooled to near absolute zero and particle detectors to record cosmic rays, high-speed subatomic particles – mostly protons – from beyond the solar system traveling through space at a significant fraction of the speed of light. No one’s sure exactly where cosmic rays originate but violent phenomena like supernovae are likely to be one source. Since start-up in May 2011 AMS had recorded over 30 billion cosmic ray events.
Among the great many speedy protons, AMS looked for high-speed electrons and their antimatter counterpart positrons. Antimatter is identical to ordinary matter except its particles have the opposite electric charge. Electrons, those little packets of energy whizzing around an atom’s nucleus, have a negative charge in our neck of the universe, but in the antimatter world, electrons are positively charged. Physicists call them positrons; the first one was discovered in 1932.
There are anti-hydrogen atoms made of oppositely charged electrons and protons. There may even be entire anti-planets, anti-stars and anti-galaxies out there. But be careful. If you happen to run into your antimatter self one day, you’ll utterly destroy one other. When matter and antimatter touch, they explode as pure energy.
Appearances to the contrary, the material universe has more than five times more “dark matter” than the normal matter – about 27% vs. 5%. No one can see dark matter because it neither shines nor reflects light of any kind – visible, radio, X-rays. We only know it’s there by its gravitational influence on ordinary matter. If it weren’t for the tug of dark matter, many galaxy clusters would simply fly apart. Dark matter also accounts for the shapes and rotations observed in individual galaxies.
Oddly enough, dark matter is thought to be its own antimatter. A leading theory says that it could be made of particles called neutralinos, which produce showers of electrons and positrons (antimatter) when they collide. In a study of 25 billion cosmic rays between May 2011 and Dec. 2012, AMS detected 6.8 million electrons and their antimatter counterpart, positrons. Of those, 400,000 positrons were found, the largest number of energetic antimatter particles directly measured and analyzed from space.
The large number of positrons points to two possible sources – dark matter particles colliding and annihilating or pulsars. A pulsar is a city-sized, rapidly rotating star that sends out beams of powerful radiation along with hordes of electrons and positrons. More data from AMS may soon allow scientists to distinguish between the two and clue us in on the nature of dark matter. Will it be neutralinos or another particle not yet on the radar? Either way, AMS will keep us hot on the trail. Read more about the results HERE.