April 4, 2013
Dark Matter Evidence From The Alpha Magnetic Spectrometer
[ Watch the Video: AMS Time Lapse Installation ]
John P. Millis, Ph.D. for redOrbit.com — Your Universe Online
For decades scientists have wondered whether a mysterious form of matter — known simply as Dark Matter since it does not interact directly with light — makes up the majority of the “stuff” in the Universe.
Researchers have pointed to the seminal work on the Bullet Cluster of galaxies as evidence that dark matter is a real substance. But similar observations of other galaxy clusters have yielded inconclusive results.
Opponents of the theory suggest that perhaps dark matter is not really matter at all. Instead perhaps our theory of gravity — Einstein´s Theory of General Relativity — is somehow flawed or incomplete. To find the answer, research is ongoing to observe, either directly or indirectly evidence that dark matter actually exists in our Universe.
Now a new study from an international collaboration of scientists has released new, compelling data that suggests that dark matter exists throughout our Universe.
Using an instrument known as the Alpha Magnetic Spectrometer (AMS), the team sorted through over 30 billion cosmic ray events — very high energy particles; mostly protons, electrons and other nuclei — that triggered the detector. They were particularly interested in the ratio of positrons to their antimatter counterpart, the electron.
Certain theories of dark matter predict that the candidate particle is of a special class of self-annihilating matter. Therefore, there is a statistical probability that dark matter collisions could release a significant amount of energy. This energy would eventually manifest itself as electron and positron pairs.
While electrons are commonly produced by several mechanisms, positrons are less prevalent — typically arising from pair production processes. If dark matter is real and theories such as supersymmetry are correct, then dark matter annihilations would cause a rise in the ratio of positions to electrons above 10 billion electron volts (10 GeV).
Using roughly 10% of the data the instrument will accumulate, the AMS sees just such a rise up to about 250 GeV. The AMS has sensitivity enough to probe even higher energies, but with fewer events in those regimes, a greater amount of data is needed to have sufficient statistics on the data.
The research also reports an isotropic distribution to the positron flux, meaning that the particles appear to come from all directions equally. This is certainly consistent with the expected dark matter distribution. However, such conclusions are rather soft, as the interstellar magnetic field can bend the bath of the particles, masking the direction from which they originated.
Therefore, researchers are not ready to call the matter closed. There is still the possibility that these particles were produced by some other mechanism, perhaps even one that we have not even imagined yet. As additional data is analyzed, the picture will hopefully come into clearer focus. But for now evidence continues to mount for the existence of dark matter.
NASA Administrator Charles Bolden had this to say on the matter:
"The AMS cosmic ray particle results announced today could help foster a new understanding of the fields of fundamental physics and astrophysics. I am confident that this is only the first of many scientific discoveries enabled by the station that will change our understanding of the universe. Multiple NASA human spaceflight centers around the country played important roles in this work, and we look forward to many more exciting results from AMS.
"For more than 50 years, NASA has pushed the boundaries beyond Earth to unveil the underlying architecture of the cosmos, revealing new knowledge about our place within it. The International Space Station is a gateway to the universe, teaching us how humans can live, work, and thrive in space as we endeavor to venture deeper into the solar system. It's a remarkable testament that the orbital laboratory could play such an important supporting role in research at the very smallest scale of the physical universe. It's proof positive the space station is humanity's greatest achievement in low-Earth orbit."
The AMS results are published in the journal Physical Review Letters.