NYU physicist Glennys Farrar has proposed an answer to one of the vexing questions of physics and astronomy: What is the origin of extremely high-energy cosmic rays and where do they get their energy? Farrar has determined that the very highest energy cosmic rays appear to come from extremely distant quasars. Furthermore, Farrar has proposed that these cosmic rays are composed of a new type of subatomic particle.
Farrar and astronomer Peter Bierman of the Max Planck Institute for Radio Astronomy studied the five most energetic cosmic rays ever detected on Earth. The researchers were able to retrace the trajectory of each cosmic ray using data collected by the Fly's Eye detector in Utah, England's Haverah Park detector and Japan's AGASA shower array. The points of origin for these 5 rays corresponded with the locations of 5 compact radio loud quasars, which are among the most powerful sources of energy in the universe. The nearest of these 5 quasars is 4-5 billion light years away. The furthest is 13-16 billion light years away.
Seemingly, Farrar's theory violates the Greisen-Zatsepin-Kuzmin (GZK) cutoff, a theoretical result that states that cosmic rays above a certain energy cannot travel more than about 60 million light years because the protons that form them are steadily sapped of energy as they collide with photons that have littered the cosmos since the Big Bang.
This seeming violation of the cutoff, combined with the absence of deflection en route from the quasar source which protons would experience due to intergalactic magnetic fields, has led Farrar to theorize that high-energy cosmic rays are not made of protons. Instead, she argues that such cosmic rays are made principally of a new subatomic particle. According to Farrar, this could be the SO, a neutral particle made up of three quarks (up, down and strange) bound together with a gluino.
The SO has at least two characteristics that would help it endure the trip across space. In contrast to protons, which are positively charged, the SO would be neutral, making it less likely to interact with the big-bang photons. Second, its predicted mass - 2-3 times that of a proton - would contribute to its resistance to energy loss.
Farrar said, "The correlation we found between the directions of these cosmic rays and the position of quasars of this very special class is extremely striking. The probability that it's just a statistical fluke is less than .5 percent. If our correlation is confirmed by future data, it will simultaneously pinpoint the astronomical objects that produce the highest energy cosmic rays, and it will also demonstrate that there must be a different type of particle than the one that is responsible for lower energy events. If so, it's amazing to realize that these events may be due to the arrival on earth of a piece of matter that has traveled three-forths of the way across the visible Universe."
Farrar's findings will be reported in an article entitled "Correlation Between Compact Radio Quasars and Ultrahigh Energy Cosmic Rays" in the October 26th issue of Physical Review Letters. Her research is funded by the National Science Foundation.
Farrar, the chair of NYU's physics department, is a theoretical elementary particle physicist specializing in "phenomenology" -- the art of confronting experiments with theory and vice versa. She also works in cosmology and astroparticle physics.