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Astronomy News - Beyond the Milky Way
First direct detection of dark matter? - 15th February 2010
The Cryogenic Dark Matter Search (CDMS) collaboration has reported two candidate events consistent with Weakly Interacting Massive Particles (WIMPs). If confirmed, this will be the first evidence that dark matter is partially composed of WIMPs. The results, published in Science, state that the signals collected during the final exposure of the detectors exceed the expected background. However, it is also noted that the detection rate was not sufficiently high to be statistically significant.
The CDMS experiment takes place in Minnesota, USA. Cryogenic detectors are placed deep underground in a mine to reduce the level of interfering background particles. The experiment aims to detect the recoil of particles in germanium and silicon crystals when struck directly by WIMPs.
|A CDMS assembly: The six detectors that form the edges of this assembly are kept at 4 degrees above absolute zero.|
Theory predicts that WIMPs should be common but the likelihood of direct collisions with nuclei in the detectors is small and background particle collisions may drown out the signal.
Dark matter may consist of Massive Astrophysical Compact Halo Objects (MACHOs), massive objects such as neutron stars or black holes drifting through space that emit little or no radiation. They would be hard to detect but would still contribute mass to the universe. These objects are composed of the matter that we are familiar with (known as baryons). The standard model of the big bang limits the amount of baryonic matter in the universe and this is not enough to account for dark matter; non-baryonic matter is required. The leading candidates are WIMPs, single particles more massive than protons and neutrons that do not interact with matter the same way as the more familiar baryonic particles. They would not emit or absorb light but would respond to gravity and the weak nuclear force. It is through these interactions that researchers hope to detect them.
Dark matter is thought by many to make up the majority of the universe's mass. Only 5% is accounted for by matter in the form of visible gas, stars and planets. An additional 70% is predicted to be in the elusive form of dark energy and the remaining 25% as dark matter.
For more on the CDMS collaboration, see http://cdms.berkeley.edu/
C. Gareth Few