Discovery Links Highest-Energy Cosmic Rays with Violent Black Holes
Credit: Stephane Coutu, Penn State
Penn State scientists and other members of the 17-nation Pierre Auger Collaboration will announce on 9 November their discovery that Active Galactic Nuclei — thought to be powered by supermassive black holes — are the most likely source of the highest-energy cosmic rays that hit Earth. Using the Pierre Auger Observatory in Argentina, the largest cosmic-ray observatory in the world, the research team has closed in on a long-standing scientific mystery by linking the sources of the origins of these mysterious highest-energy particles to the locations of nearby galaxies that have active nuclei in their centers. The results will appear in the 9 November issue of the journal Science.
"This discovery not only reveals the likely origins of the highest-energy particles in the universe, but it also reveals, for the first time, that those particles are almost surely protons," says Paul Sommers, professor of physics at Penn State and associate director of the Penn State Institute for Gravitation and the Cosmos. "With this knowledge, it now becomes possible to study the properties of particle interactions at these energies, which are much higher than can be attained using particle accelerators on Earth."
Sommers has worked on the Auger Project since its inception in 1992 and was the task leader for its air fluorescence detectors during the design-and-development stages of the project. He subsequently served as the co-chair of the Auger Project's international Collaboration Board.
Most galaxies have supermassive black holes at their centers, but only a fraction of them are the kind of Active Galactic Nuclei (AGNs) that long have been considered sites where high-energy particle production might take place. These AGNs swallow gas, dust, and other matter from their host galaxies and spew out particles and energy. The exact mechanism of how AGNs can accelerate particles to energies 100-million times higher than the most powerful particle accelerator on Earth is still a mystery.
A surface detector station with the Andes in the background. Credit: Pierre Auger Observatory
"We have taken a big step forward in solving the mystery of the nature and origin of the highest-energy cosmic rays, first revealed by French physicist Pierre Auger in 1938," said Nobel Prize winner James Cronin, of the University of Chicago, who conceived the Pierre Auger Observatory together with Alan Watson of the University of Leeds. "We find the southern hemisphere sky as observed in ultra-high-energy cosmic rays is non-uniform. This is a fundamental discovery. The age of cosmic-ray astronomy has arrived. In the next few years our data will permit us to identify the exact sources of these cosmic rays and how they accelerate these particles."
Cosmic rays are protons and atomic nuclei that travel across the universe at close to the speed of light. When these particles smash into the upper atmosphere of our planet, they create a cascade of secondary particles called an air shower that can spread across 40 or more square kilometers (15 square miles) as they reach the Earth's surface.
"This result heralds a new window to the nearby universe and the beginning of cosmic-ray astronomy," said Watson, a spokesperson of the Pierre Auger Collaboration. "As we collect more and more data, we may look at individual galaxies in a detailed and completely new way. As we had anticipated, our observatory is producing a new image of the universe based on cosmic rays instead of on light."
The Pierre Auger Observatory is a hybrid detector. On the hill is one of the 4 Fluorescence Detector buildings and communications tower. In the bottom foreground is one of the 1,600 Surface Detectors. Credit: Pierre Auger Observatory
The Pierre Auger Observatory records cosmic-ray showers through an array of 1,600 particle detectors placed 1.5 kilometers (about one mile) apart in a grid spread across 3,000 square kilometers (1,200 square miles). Twenty-four specially designed telescopes record the emission of fluorescence light from the air shower. The combination of particle detectors and fluorescence telescopes provides an exceptionally powerful instrument for this research.
"It's difficult to truly comprehend the scale of the effort required to investigate these extremely rare and most energetic of particles," says Stephane Coutu an associate professor of physics and astronomy and astrophysics at Penn State and a member of the Auger team since 1997. "The detectors are deployed out on the Argentine pampa nearly a mile apart, over an area the size of Rhode Island, so that one can seldom even see more than two or three of the detectors with the naked eye. Yet dozens of detectors can record particles of an air shower produced by a single energetic cosmic ray. It really is a sobering experience being out there and realizing that such high-energy particles exist in Nature."
To aid in visualizing the layout of the Auger Observatory, the Penn State team has put together freely downloadable movies and an interactively explorable 3-D model of the observatory structures and detectors using Google Earth. The movie in English can be downloaded here. The model files, other versions of the movie, and more information sources are on the Web at <http://www.phys.psu.edu/~coutu/Auger_Google_Earth.htm>, along with instructions on installing and using the model.
"Spending a few minutes navigating around the Argentine site, tilting the field of view and flying over the detector array in Google Earth, really brings home the scale of the task we have undertaken," Coutu comments. "Seeing the first hints of the astrophysical origins of these extraordinarily energetic particles is a welcome reward after the many years of effort it took to design and deploy this largest of observatories."
An aerial view of the Fluorescence Detector building at Los Leones. The building contains 6 bays, each of which houses a complete telescope and camera assmebly viewing a part of the sky over the array. The communications tower is behind the detector building. Credit: Pierre Auger Observatory
The Auger collaboration discovered that the 27 highest-energy events, with energy above 57 EeV, do not come equally from all directions. Comparing the clustering of these events with the known locations of 381 AGNs, the collaboration found that most of these events correlated well with the locations of AGNs in some nearby galaxies, such as Centaurus A.
While the observatory has recorded almost a million cosmic-ray showers, only the rare, highest-energy cosmic rays can be linked to their sources with sufficient precision because they are deflected less by magnetic fields. Unfortunately, such energetic cosmic rays hit Earth at a rate of only about one per square kilometer per century — requiring a very large observatory.
The Auger collaboration is developing plans for a second, larger installation in Colorado to extend coverage to the entire sky while substantially increasing the number of high-energy events recorded.
The observatory is named for French scientist Pierre Victor Auger (1899-1993), who in 1938 was the first to observe the extensive air showers generated by the interaction of high-energy cosmic rays with the Earth's atmosphere.
CONTACTS:
Barbara K. Kennedy at Penn State (PIO): (+1)814-863-4682, science@psu.edu
Paul Sommers: (+1)814-865-4306, sommers@phys.psu.edu
Stephane Coutu: (+1)814-865-2015, coutu@phys.psu.edu
IMAGES AND MORE INFORMATION:
Freely downloadable movies and an interactively explorable 3-D model of the observatory structures and detectors using Google Earth. The movie in English can be downloaded here. The model files, other versions of the movie, and more information sources are on the Web at
<http://www.phys.psu.edu/~coutu/Auger_Google_Earth.htm>, along with instructions on installing and using the model.
More photos, as well as press information from the countries participating in the Auger Project are on the Web at <http://www.auger.org/media>.
Auger Observatory funding agencies (by country):
--- International: ALFA-EC / HELEN, UNESCO
--- Argentina: Comisión Nacional de Energía Atómica, Fundación Antorchas, Gobierno De La Provincia de Mendoza, Municipalidad de Malargüe
--- Australia: Australian Research Council
--- Brazil: Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq),
Financiadora de Estudos e Projetos (FINEP), Fundação de Amparo à Pesquisa do Estado de Rio de Janeiro (FAPERJ), Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), Ministério de Ciência e Tecnologia (MCT)
--- Czech Republic: Ministry of Education, Youth and Sports of the Czech Republic
--- France: Centre National de la Recherche Scientifique (CNRS), Conseil Régional Ile-de-France, Département Physique Nucléaire et Corpusculaire (PNC-IN2P3/CNRS), Département Sciences de l'Univers (SDU-INSU/CNRS)
--- Germany: Bundesministerium für Bildung und Forschung (BMBF), Deutsche Forschungsgemeinschaft (DFG), Finanzministerium Baden-Württemberg, Helmholtz-Gemeinschaft Deutscher Forschungszentren (HGF), Ministerium für Wissenschaft und Forschung, Nordrhein Westfalen, Ministerium für Wissenschaft, Forschung und Kunst, Baden-Württemberg
--- Italy: Istituto Nazionale di Fisica Nucleare (INFN), Ministero dell'Istruzione, dell'Università e della Ricerca (MIUR)
--- Mexico: Consejo Nacional de Ciencia y Tecnología (CONACYT)
--- Netherlands: Ministerie van Onderwijs, Cultuur en Wetenschap, Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), Stichting voor Fundamenteel Onderzoek der Materie (FOM)
--- Poland: Ministry of Science and Higher Education
--- Portugal: Fundação para a Ciência e a Tecnologia
--- Slovenia: Ministry for Higher Education, Science, and Technology, Slovenian Research Agency
--- Spain: Comunidad de Madrid, Consejería de Educacíon de la Comunidad de Castilla La Mancha, FEDER funds, Ministerio de Educacíon y Ciencia, Xunta de Galicia
--- United Kingdom: Science and Technology Facilities Council
--- United States: Department of Energy, Grainger Foundation, National Science Foundation
Auger Observatory collaborating institutions (by country):
--- Argentina: Centro Atómico Bariloche (CNEA); Instituto Balseiro (CNEA & UNCuyo); CONICET, Instituto de Astronomía y Física del Espacio (CONICET), Laboratorio Tandar (CNEA); CONICET; Univ. Tec. Nac. (Reg. Buenos Aires), Pierre Auger Southern Observatory, Universidad Nacional de la Plata; IFLP/CONICET; Univ. Nac. de Buenos Aires, Universidad Tecnológica Nacional - Regionales Mendoza y San Rafael
--- Australia: University of Adelaide
--- Bolivia: Universidad Catolica de Bolivia, Universidad Mayor de San Andrés
--- Brazil: Centro Brasileiro de Pesquisas Fisicas (CBPF), Pontifícia Universidade Católica, Rio de Janeiro, Universidade de Sao Paulo, Inst. de Fisica, Universidade Estadual de Campinas (UNICAMP), Universidade Estadual de Feira de Santana (UEFS), Universidade Estadual do Sudoeste da Bahia (UESB), Universidade Federal da Bahia, Universidade Federal do ABC (UFABC), Universidade Federal do Rio de Janeiro (UFRJ), Universidade Federal Fluminense
--- Czech Republic: Charles University Prague, Institute of Particle and Nuclear Physics, Institute of Physics (FZU) of the Academy of Sciences of the Czech Republic
--- France: Institut de Physique Nucléaire, Orsay (IPNO), Laboratoire AstroParticule et Cosmologie Université Paris VII, Laboratoire de l'Accélérateur Linéaire (LAL), Orsay, Laboratoire de Physique Nucléaire et de Hautes Energies (LPNHE), Université Paris 6, Laboratoire de Physique Subatomique et de Cosmologie (LPSC) - Grenoble
--- Germany: Bergische Universität Wuppertal, Forschungszentrum Karlsruhe - Institut für Kernphysik, Forschungszentrum Karlsruhe - Institut für Prozessdatenverarbeitung und Elektronik, Max-Planck-Institut für Radioastronomie and Universität Bonn, Rheinisch-Westfälische Technische Hochschule (RWTH) Aachen, Universität Karlsruhe (TH) - Institut für Experimentelle Kernphysik (IEKP), Universität Siegen
--- Italy: Dipartimento di Fisica dell'Università and INFN, L'Aquila, Dipartimento di Fisica dell'Università and Sezione INFN, Milano, Dipartimento di Fisica dell'Università di Napoli “Federico II” and Sezione INFN, Napoli, Dipartimento di Fisica dell'Università di Roma “Tor Vergata” and Sezione INFN Roma II, Dipartimento di Fisica e Astronomia dell'Università di Catania & Sezione INFN, Catania, Dipartimento di Fisica Sperimentale dell'Università and Sezione INFN, Torino, Dipartimento di Fisica, Università del Salento and Sezione INFN, Istituto di Fisica dello Spazio Interplanetario (INAF), Dipartimento di Fisica Generale dell'Università and Sezione INFN, Torino, Laboratori Nazionali del Gran Sasso, INFN, Osservatorio Astrofisico di Arcetri
--- Mexico:?Benemérita Universidad Autónoma de Puebla (BUAP), Centro de Investigación y de Estudios Avanzados del IPN (CINVESTAV), Universidad Michoacana de San Nicolás de Hidalgo, Universidad Nacional Autónoma de México
--- Netherlands: Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud Universiteit , Kernfysisch Versneller Instituut (KVI), Rijksuniversiteit Groningen, Nationaal Instituut voor Kernfysica en Hoge Energie Fysica (Nikhef), Stichting Astronomisch Onderzoek in Nederland (ASTRON), Dwingeloo
--- Poland: Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, University of Lodz
--- Portugal: Laboratory of Instrumentation and Experimental Particle Physics (LIP)
--- Slovenia: University of Nova Gorica
--- Spain: Instituto de Física Corpuscular, CSIC-Universitat de València, Universidad Complutense de Madrid, Universidad de Alcalá de Henares, Universidad de Santiago de Compostela, University of Granada
--- United Kingdom: Oxford University, University of Leeds, School of Physics & Astronomy
--- United States: Argonne National Laboratory, Case Western Reserve University, Colorado School of Mines, Colorado State University, Fort Collins, Colorado State University, Pueblo, Columbia University, Fermi National Accelerator Laboratory , Louisiana State University, Michigan Technological University, New York University, Northeastern University, Ohio State University, Pennsylvania State University, Southern University, University of California, Los Angeles, University of Chicago, University of Colorado, University of Hawaii, University of Minnesota, University of Nebraska, University of New Mexico, University of Utah, University of Wisconsin-Madison, University of Wisconsin-Milwaukee
--- Vietnam: Institute of Nuclear Science and Technology of Hanoi (INST)