14 DAY TRIAL // Earth, like many other bodies in space, is constantly being bombarded with streams of highly energetic sub-atomic particles of matter, coming from all directions. But, while some emissions of particles inside the atmosphere can be explained relatively easy, one type of cosmic rays remained, so far, mostly a mystery. From time to time, faint blue flashes of radiation are being emitted, when particles traveling faster than light hit the atmosphere.
This posed a physical paradox, since nothing in the universe can travel faster than the speed of light, while cosmic rays showed evidence that such particles could exist. These particles of matter raining down on Earth from outer space could average a density of tens of thousands of elementary particle per second per square meter. During the study of what could emit such particles, observations taken from Pierre Auger Cosmic Ray Observatory suggested that the most energetic particles emitted in the universe come from the central region of active galaxies.
However, most of the particles that hit Earth come from within our own galaxy, originating in unknown sources and thus preventing the process of understanding the phenomena. The most popular theory regarding the source of these high energy particles was formulated more than 50 years ago by Enrico Fermi from the University Of Chicago, and stated that they could be a result of the shock wave of exploding stars, but the possibility of it remains yet untested.
Scott Wakely, assistant professor in physics at the University of Chicago, has been recently granted a funding of $625,000 from the National Science Foundation to design a device capable of revealing the true nature of these cosmic rays. This device was supposed to be able to detect Cerenkov radiation, that is emitted when particles traveling faster than light pass through the atmosphere.
But this time around the same paradox was encountered as well - of particles traveling faster than the speed of light. Scott Wakely explains that the fact that sub-atomic particles seem to travel faster than the speed of light is, in fact, merely an illusion. Photons traveling through voids define the maximum speed in the universe; however, in air and water, light travels slower than in a vacuum; thus, the conclusion that only light can travel faster than light was reached.
As these energetic photons hit the atmosphere, they produce an effect similar to the sonic boom, emitting electromagnetic radiation in the process, called Cerenkov radiation. Using the Cerenkov detection technique presents difficulties in measuring the energy and the mass of the cosmic rays since, as the high-energy particles hit the upper layer of Earth's atmosphere, they decay in a shower of other particles that are impossible to measure directly.
During the process of entering the atmosphere, the cosmic rays produce two distinct Cerenkov radiation emissions: one as the energetic particle enters the atmosphere, and the second as a result of the stream of particles resulted from the decay of the original one. According to Wakely, the Cerenkov detection technique can be greatly improved while using a combination of balloon-borne instruments to gather precise data with the VERITAS and HESS experiments, that have a greater detection area and less precision.
The second approach would involve avoiding the build of extensive experiments on the ground, and flying the instruments at high altitudes with helium balloons, where the atmosphere is thiner.
The large majority of cosmic ray emissions consists mostly of sub-atomic charged particles such as protons. However, studies show that they can also contain nuclei of heavy elements such as iron which, when traveling at a speed close to that of the light, emit about 700 times more light than a single proton.