Professor Flavio Cavanna “What is Dark Matter and why is it so mysterious?” Written by Veronica Watters, Sarah McMahon, and Grey Hamilton Professor Flavio Cavanna, researcher at Gran Sasso National Laboratory and professor of physics at the University of L’Aquila, lectured on the subject of dark matter. Professor Cavanna used examples from astronomy and physics to prove that some unknown force exists, holding our universe together. As of now, we have given this unknown the name dark matter and dark energy. So far, dark matter is defined as matter in the universe that is not visible to humans and their technology. Scientists are convinced dark matter exists because of calculations done using the Doppler Effect. According to the Doppler Effect, the speed of rotating galaxies is too great for the amount of visible matter. Without more matter, the speed of rotation would cause the galaxies and universe to fly apart instead of being held together by gravity. Scientists believe that up to 90 percent of the universe is made up of dark energy and dark matter. Little is known about dark energy. Scientists believe dark energy could close the universe’s energy balance. Further evidence that most of the matter in our universe is dark is provided by calculations using gravitational lensing. Gravitational lensing is the distortion of distant objects’ light being bent by a huge source of mass, usually a cluster of galaxies. In effect, the more distorted the distant object, the larger the source of distortion (the mass). Galaxy clusters typically cause a thirty arc second distortion. Using calculations from gravitational lensing, scientists found that not enough visible matter was contained in the galaxy clusters to cause the distortion observed. Again scientists found that visible matter only attributed to ten percent of that matter needed to cause the lensing effect. When galaxies form clusters, they contain enormous amounts of hot gas between them. The color of the hydrogen gas indicates a very high temperature. The high temperature indicates a high energy. By knowing the temperature, energy and distribution of the hot gas, the force of the gravity within the clusters can be calculated. Using the equation E=mc^2, the amount of visible matter in the galaxy clusters is not massive enough to account for the enormous energy amounts indicated by the color of the hydrogen gas. To explain the “missing” mass, scientists have come up with the concept of dark matter. While scientists believe dark matter exists, they only have theories explaining the properties of this new energy and matter. Scientists believe dark matter has not been detected because it does not have a high probability of interaction with normal matter. Since dark matter does not interact with light, scientists have determined that dark matter lacks an electromagnetic force. However, a gravitational force could explain the large amount of mass dark matter is believed to have. If dark matter has a weak force, it is possible experiments could be designed to detect this elusive particle. Until detection, the properties of dark matter can only be theorized. Strong evidence of dark matter’s existence comes from photographs taken by the Hubble Space Telescope’s. In 2004, the Hubble observed a collision of two galaxy clusters, the most massive bodies in the universe. When these two clusters collided, a ripple effect was observed. Scientists believe the ripple effect was caused by the collision of the massive amounts of dark matter present in the galaxy clusters. Scientists believe dark matter and energy exists in “halos” around galaxies and galaxy clusters. Within the Milky Way and other galaxies, scientists theorize dark matter clumps into “subhalos”. The subhalos of dark matter are believed to cause the warping of the tips Milky Way’s arms. The ripple and warping of visible matter is strong evidence for the existence of dark matter. Dark Matter is one of the current projects attempting to detect dark matter at Gran Sasso National Laboratory. DAMA is the only experiment to claim having detected dark matter particles. After seven years of observation, the DAMA project has seen a cycle in the supposed dark matter particles detected. A flux of interactions was observed during the summer, because the earth’s rotation corresponds with the rotation of the galaxy’s arm and the dark matter is closer. During the winter the number of interactions decreased as the rotation moved away from the dark matter. DAMA’s detection is indirect because it cannot distinguish between dark matter particles and background. Of the experiments that disagree with DAMA’s findings, the WIMP Argon Programme experiment was discussed. WIMPs are weakly interacting massive particles, the name scientists have given to dark matter. WARP uses a large argon liquid scintillator in detecting WIMP particles. If dark matter actually carries a weak charge, WARP would detect the particles when a WIMP collides with the argon particle and causes the argon nucleus to recoil. No signal was found in the region expected. Because no experiments besides DAMA have found a WIMP signal, many are skeptical about the interpretation of the DAMA results. At this point dark matter is still an unknown, seeing as there is no direct proof of the existence of said matter. Though strong evidences have been produced by experimentation and observation (i.e.: WARP, and the Hubble space telescope pictures), the fact remains that a direct and undeniable instance of dark matter has yet to be found. In fact, a majority of the current experiments designed to look for dark matter, have not found any evidence, at all, of the existence of dark forces. The results are inconclusive, but the search is still on for the elusive dark matter.