NASA Hot On The Trail Of Dark Matter-antimatter Connection

The AMS operates in space from the International Space Station. Its purpose is to study cosmic rays in search of dark matter and antimatter. Credit: NASA

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.

When antimatter (left) meets normal matter the two annihilate each in a blaze of pure energy. Credit: NASA

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.

This Hubble Space Telescope composite image shows a ghostly ripples of dark matter in the galaxy cluster Cl 0024+17. The ripples aren’t really glowing but inferred by how the gravity of the foreground galaxy cluster bends the light of a more distant cluster (blue specks) in the background. They formed during a collision of the two clusters in the distant past. Click to read more. Credit: NASA/ESA

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.

An artist’s concept of the newly discovered pulsar. Clouds of charged particles like electrons and positrons move along the pulsar’s magnetic field lines (blue) and create a lighthouse-like beam of gamma rays (purple) and high-speed particles. Credit: NASA

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.

5 Responses

  1. Lynn

    Hi Bob
    What on earth is the Boltzman, is it just a theory as I tried to read up on it but a bit too much physics for me and a few of the articles are from 2007 and 2008 etc but the one mentioned above is 2013, and did an asteroid really hit Jupiter recently, I just can’t make sense of it, so i’m hoping you do as your good at physics and i’ve not recently left a comment, but just wanted to say that I still read your blogs every night and I’ve been reading some fascinating things that you have written 🙂

    1. astrobob

      No asteroid we know of has hit Jupiter recently though it has been struck a few times in the past that we’re aware of. The Boltzmann thing has to do with how organized matter can spontaneously form out of unorganized matter in the universe including something as complicated as a living entity. It’s a hypothesis.

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