Scientists link mysterious highest-energy cosmic rays with violent black holes

The results will appear in the Nov. 9 issue of the journal Science.

Active Galactic Nuclei (AGN) are thought to be powered by supermassive black holes that are devouring large amounts of matter. They have long been considered sites where high-energy particle production might take place. They swallow gas, dust and other matter from their host galaxies and spew out particles and energy. While most galaxies have black holes at their center, only a fraction of all galaxies have an AGN. 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.

“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 light.”

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.

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. Auger scientists so far have recorded 77 cosmic rays with energy above 4 x1019 electron volts, or 40 EeV. This is the largest number of cosmic rays with energy above 40 EeV recorded by any observatory. At these ultra-high energies, the uncertainty in the direction from which the cosmic ray arrived is only a few degrees, allowing scientists to determine the location of the particle’s cosmic source.

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 318 Active Galactic Nuclei, the collaboration found that most of these events correlated well with the locations of AGNs in some nearby galaxies, such as Centaurus A.

“Low-energy cosmic rays are abundant and come from all directions, mostly from within our own Milky Way galaxy. Until now the only source of cosmic ray particles known with certainty has been the sun. Cosmic rays from other likely sources such as exploding stars take meandering paths through space so that when they reach Earth it is impossible to determine their origins. But when you look at the highest-energy cosmic rays from the most violent sources, they point back to their sources. The challenge now is to record enough of these cosmic bullets to understand the processes that hurl them into space,” said Paul Mantsch, project manager of the Pierre Auger Observatory.

Cosmic rays with energy higher than about 60 EeV lose energy in collisions with the cosmic microwave background, radiation left over from the Big Bang that fills all of space. But cosmic rays from nearby sources are less likely to lose energy in collisions on their relatively short trip to Earth. Auger scientists found that most of the 27 events with energy above 57 EeV came from locations in the sky that include the nearest AGNs, within a few hundred million light years of Earth.

Scientists think that most galaxies have black holes at their centers, with masses ranging from a million to a few billion times the mass of our sun. The black hole at the center of our Milky Way galaxy weighs about 3 million solar masses, but it is not an AGN. Galaxies that have an AGN seem to be those that suffered a collision with another galaxy or some other massive disruption in the last few hundred million years. The AGN swallows the mass coming its way while releasing prodigious amounts of radiation. The Auger result indicates that AGNs may also produce the universe's highest-energy particles.

Cosmic-ray astronomy is challenging, because low-energy cosmic rays provide no reliable information on the location of their sources: as they travel across the cosmos, they are deflected by galactic and intergalactic magnetic fields that lead to blurry images. In contrast, the most energetic particles come almost straight from their sources, as they are barely affected by the magnetic fields. Unfortunately, they hit Earth at a rate of only about one event per square kilometer per century, which demands a very large observatory.

Because of its size, the Auger Observatory can record about 30 ultra-high-energy events per year. 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.

“Our current results show the promising future of cosmic-ray astronomy,” said Auger cospokesperson Giorgio Matthiae, of the University of Rome. “So far we have installed 1400 of the 1600 particle detectors of the Auger Observatory in Argentina. A northern site would let us look at more galaxies and black holes, increasing the sensitivity of our observatory. There are even more nearby AGNs in the northern sky than in the southern sky.”

The Pierre Auger Observatory is being built by a team of more than 370 scientists and engineers from 17 countries.

“The collaboration is a true international partnership in which no country contributed more than 25 percent of the US$54-million construction cost,” said Danilo Zavrtanik, of the University of Nova Gorica and chair of the Auger Collaboration Board. The names of the funding agencies contributing to the Pierre Auger Observatory as well as the names of the participating institutions are listed below.

Groundbreaking for the southern hemisphere site of the Pierre Auger Observatory took place on March 17, 1999, in Argentina’s Mendoza Province. Following a period of detector deployment and testing, scientific data collection began in January, 2004.

“Argentina is pleased to host and participate in this unique scientific endeavor,” said Alberto Etchegoyen, of Comisión Nacional de Energía Atómica and Southern Observatory spokesperson, “and now, looking back into these years of efforts and excitement, a feeling of gratitude and respect arises for all collaboration members who took care of every single minor detail leading to today’s announcement.”

Source: Fermi National Accelerator Laboratory

Study confirms 1966 prediction: The most energetic particles in the universe are not from the neighborhood
Final results from the University of Utah’s High-Resolution Fly’s Eye cosmic ray observatory show that the most energetic particles in the universe rarely reach Earth at full strength because they come from great distances, so most of them collide with radiation left over from the birth of the universe.
Human genetic variation -- Science's 'Breakthrough of the Year'
In 2007, researchers were dazzled by the degree to which genomes differ from one human to another and began to understand the role of these variations in disease and personal traits. Science and its publisher, AAAS, the nonprofit science society, recognize “Human Genetic Variation” as the Breakthrough of the Year, and identify nine other of the year’s most significant scientific accomplishments in the 21 December issue.
Radiation flashes may help crack cosmic mystery
Faint, fleeting blue flashes of radiation emitted by particles that travel faster than the speed of light through the atmosphere may help scientists solve one of the oldest mysteries in astrophysics.
Searching for Exotic Particles from Cosmic-Ray Collisions
Our planet is constantly bombarded with cosmic rays. Most collide with atoms in our atmosphere, producing sprays of particles that fall to the ground, thousands striking each square meter every second. Cosmic rays with extremely high energies are infrequent, but their interactions in the atmosphere open a tiny but important window to ultra-high-energy physics – a window that even the most advanced particle accelerators are incapable of achieving. Recently, three physicists took a peek in.
Messengers from the Extreme Universe
A unique observatory in a remote location in Argentina is starting to unravel the mysteries of High Energy Cosmic Rays. There is no scientific consensus on the source of these particles which the shower the Earth at energies 10 million times higher than can be produced in particle accelerators! But the Pierre Auger Observatory is shedding new light on these energetic particles from space and using them as messengers to tell us more about the wider Universe.
Ultra-High Energy Cosmic Particles Produce Unusual Radio Flash
New radio telescope sees and hears brightest radio blasts on the sky

Using the LOPES experiment, a prototype of the new high-tech radio telescope LOFAR to detect ultra-high energy cosmic ray particles, a group of astrophysicists, in collaboration of Max-Planck-Gesellschaft and Helmholtz-Gemeinschaft, has recorded the brightest and fastest radio blasts ever seen on the sky. The blasts, whose detection are reported in this week's issue of the journal Nature, are dramatic flashes of radio light that appear more than 1000 times brighter than the sun and almost a million times faster than normal lightning. For a very short moment these flashes - which had gone largely unnoticed so far - become the brightest light on the sky with a diameter twice the size of the moon.
Cosmic Ray Observatory to Resolve Puzzling Mysteries
A groundbreaking ceremony will be held 9 a.m. MDT Saturday Aug. 28 in the desert southwest of Delta, Utah, for the Telescope Array – a Japanese and American cosmic ray observatory designed to find the source of the most energetic particles in the universe.
“This is the first step towards implementation of an $18 million cosmic ray project to resolve the puzzling mysteries of the highest-energy cosmic rays,” says Kai Martens, an assistant professor of physics at the University of Utah.

Britain's top prizes for physics announced
Research that revealed for the first time that the Earth’s core is almost as hot as the Sun, groundbreaking new work on cosmic strings and black holes, and a scientist who believes he could build a viable desktop quantum computer by 2010, have won Britain’s most prestigious prizes for physics, the Institute of Physics Awards 2006.

Scientists link mysterious highest-energy cosmic rays with violent black holes

Related stories:

News discussion: