The existence of dark matter has been known for decades, but working out what it is actually made from has been a frustrating quest. Now, however, Professor David Cline has told a UCLA symposium of the finding of what could be the first cold dark matter particle, an object weighing 30 billion electron volts.
The first evidence for dark matter emerged in 1932 when Jan Oort noted that objects are circling the galactic plane as if our galaxy has substantially more mass than we can see. Further study on other galaxies found the same pattern. Two main theories emerged: Weakly Interacting Massive Particles (WIMPS) or Massive Compact Halo Objects (MACHOs). The first involves subatomic particles with no electromagnetic charge or strong nuclear interaction; the second posits objects the size of planets or stars that don't shine.
The problem is far from trivial. It is estimated that the dark matter we cannot see accounts for more than five times as much mass in the universe as the ordinary matter we can. Over time the weight of scientific support has shifted to the idea that WIMPS account for most of what we are missing, but finding them has been more of a problem. Neutrinos were thought to be the answer, but the neutrinos left over from the formation of the universe travel too fast, and so would be too evenly spread, to account for the mass clumped around galaxies.
What is needed is “cold dark matter” particles, ones that travel slowly enough that those produced in the big bang would have clumped together in the spots that became modern day galaxies.
Every two years UCLA convenes a symposium to discuss progress in the search for dark matter of one form or another. Nothing has yet been published, but Cline, of the home campus's College of Letters and Science, commented, "At this symposium, it was obvious that excitement is building in the fields of dark matter theory and, especially, detection."
The Fermi telescope has found mysterious gamma rays, which Cline thinks may be emitted by the particles. Attempts to get WIMPs to interact with atomic nuclei in underground laboratories have failed to find anything, but Cline said, "there is no incompatibility [in these detectors' null results] with the interesting excess in the FERMI data."
Subatomic particles are classified by their mass, but by the famous E=mc2 mass can be converted to energy, making electron volts, a unit of energy, often the favored way to describe them. For comparison, protons have a mass of just under a billion electron volts.
"Because dark matter makes up the bulk of the mass of galaxies and is fundamental in the formation of galaxies and stars, it is essential to the origin of life in the universe and on Earth," said Cline.