In a paper published in today's Physical Review Letters, the team of scientists explain how they have been able to determine an approximate location of the gamma rays place of origin within the Milky Way based on observations of the secondary, or air shower, particles that are generated when gamma rays hit Earth's atmosphere. These air shower particles are detected as they pass through the water in the 6-million-gallon pond that comprises the Milagro telescope and create a phenomenon called Cerenkov radiation. This Cerenkov radiation produces visible and ultraviolet photons that are detected by the telescope's 737 floating photon detectors. The gamma rays that enter the atmosphere are the same as the photons that make up visible light, but are roughly one trillion times more energetic than visible light.
According to Gus Sinnis, the Los Alamos astrophysicist in charge of the Milagro telescope, "The gamma rays we observed at Milagro might very well be particle fragments that were scattered across the galaxy when even higher energy cosmic rays struck the matter distributed throughout the Milky Way. These cosmic rays may, in turn, have come from a collapsing star or a supermassive black hole."
With the ability to continuously monitor the entire Northern hemisphere sky in the 1 TeV energy range, Milagro is the largest gamma ray detector of its kind in the United States. The latest discovery is the result of an analysis that isolated roughly 70,000 TeV gamma-ray events emanating from within a region of the Milky Way plane out of roughly 150 billion TeV-level events recorded by Milagro for the three years beginning in July 2000.
In addition to researchers from Los Alamos, the Milagro Milky Way gamma ray team includes researchers from George Mason University, New York University, Michigan State University, the University of California-Irvine, University of California-Santa Cruz, University of Maryland-College Park, University of New Hampshire and the University of Wisconsin.
The Milagro telescope has been in operation at the Laboratory's Fenton Hill research site since 1998. The continuing operation of Milagro is made possible by support from the National Science Foundation, the Department of Energy's Office of Science, Los Alamos National Laboratory and the University of California's Institute of Geophysics and Planetary Physics.
Los Alamos National Laboratory, a multidisciplinary research institution engaged in strategic science on behalf of national security, is operated by Los Alamos National Security, LLC, a team composed of Bechtel National, the University of California, The Babcock & Wilcox Company, and Washington Group International for the Department of Energy's National Nuclear Security Administration.
Los Alamos enhances national security by ensuring the safety and reliability of the U.S. nuclear stockpile, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to energy, environment, infrastructure, health, and global security concerns.