Artwork by Rachel Wilson.
Dark matter is believed to account for about 80 percent of the mass of the universe; however, since it does not emit any light, the only proof it exists is the effects it has on objects around it. Physicists strongly believe that the amount of visible mass in our galaxy, the Milky Way, is not enough to keep it in the spiral formation that it sits in. There must be dark matter there, otherwise the galaxy would fly off in all directions out to infinity.
Astronomer, Fritz Zwicky first proposed the existence of dark matter in the 1930s when he calculated that the amount of ordinary matter in the Coma cluster of galaxies wasn’t enough to keep the cluster from flying apart. Additional, unseen material could provide the extra gravitational tug, he suggested. Since the 1970s, astronomers have accumulated further evidence that the Milky Way and other galaxies are bathed in dark matter.
“Many different measurements in astronomy now indicate that we really only understand 5% of what the universe is made of. Of the other 95% of the mass/energy that comprises the universe we know almost nothing. Of this 95% about 20% is dark matter and the other 75% is dark energy. About dark energy we don’t have a clue – except that it is there. We DO have ideas what the dark matter could be. Some people think it could be made of MACHOS – massive compact halo objects – things like dark burnt out stars that we can’t see. Other people think it could be made of WIMPS – weakly interacting massive particles that are extremely difficult to detect in any kind of physical experiment,” said TJ Physics Teacher, Nelson Vore.
Analyzing results of the Cryogenic Dark Matter Search (CDMS) experiment in the northern Minnesota Soudan mine, physicists report the possible detection of particles of dark matter. The experiment relies on thirty detectors made of germanium and silicon crystals cooled to just above absolute zero. The detectors record tiny vibrations imparted by a proposed type of dark matter called weakly interacting massive particles, or WIMPs, which are among the most popular candidates for dark matter. Recently, the detectors in the mine recorded two hits with characteristics consistent with those expected from WIMPs.
WIMPs streaming in from space would very rarely jostle the germanium nuclei, some 800 meters underground in the Soudan mine, generating a tiny amount of heat and slightly altering the charge on the detectors in a characteristic pattern. When such an interaction happens, a WIMP careens like a billiard ball off an atom, the theory goes. But the collision leaves behind a unique signature in the form of a small amount of heat, which can be detected, and also creates charged atoms, or ions, that are detectable.
The team behind the experiment cautions that there is a one-in-four chance that the particles detected are not dark matter but ordinary subatomic particles such as neutrons. Lauren Hsu, one of the members of the team said, “Physicists typically require a much lower chance that a signal is false before regarding a result as conclusive.”
Astronomer, Fritz Zwicky first proposed the existence of dark matter in the 1930s when he calculated that the amount of ordinary matter in the Coma cluster of galaxies wasn’t enough to keep the cluster from flying apart. Additional, unseen material could provide the extra gravitational tug, he suggested. Since the 1970s, astronomers have accumulated further evidence that the Milky Way and other galaxies are bathed in dark matter.
While astronomers need dark matter to explain the growth and motions of galaxies, particle physicists who subscribe to a theory called supersymmetry have proposed that every subatomic particle has an as yet undetected heavier partner. The least massive, electrically neutral of those partners might be the WIMP.
The Large Hadron Collider could also present further evidence of the existence of dark matter, ideally in the first half of 2010. “One reason the LHC in Switzerland is such a big deal is that it might answer the question of ‘what is dark matter?’” said Vore.
According to theorist, Craig Hogan, three or four more WIMP-like interactions recorded over the next few years by the experiment, now being upgraded with detectors containing three times as much germanium, would constitute proof of dark matter. This would give scientists an entire new form of matter to study. Vore said, “Whenever you get the first look at something, for the first time, often all sorts of huge revolutionary discoveries are made.”
