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Universe's high-energy haze gets murkier

The universe's most powerful particle accelerators are responsible for just a fraction of the fog of gamma-ray light beyond the Milky Way, a new study suggests. The source of the rest remains a mystery, but dark matter could be a contributor.
The gamma-ray sky is dominated by the glow of our Milky Way as well as other known galaxies and individual neutron stars. But the universe is also aglow with a diffuse haze of gamma-ray light, produced by sources that may be too distant, dim, or diffuse to resolve individually.

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Ultra-high energy cosmic rays
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Astrophysicists ponder whether ultrahigh-energy particles really do come from the centre of galaxies.

Astronomers using a giant array of detectors in Argentina had thought three years ago they were close to solving the mystery of the Universe's highest energy cosmic rays. But the same researchers have now had to backpedal in the face of new observations that threaten their earlier conclusions about the origins and composition of these intense particles.
In 2007, the team at the Pierre Auger Observatory in Mendoza, Argentina, found that a handful of cosmic-ray detections suggested a tentative alignment between these incoming particles and active galactic nuclei (AGN) - a hint that the supermassive black holes in the AGN might be the long-sought cosmic particle accelerators that give the rays their huge energies.
But at a meeting of the American Physical Society in Washington DC on 16 February, the Auger team revealed new data that weaken the link between the particles and the AGN.

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A new map of the sky made using a telescope sensitive to the most powerful kind of light, called gamma radiation, shows that some cosmic rays are coming from those exploding stars known as supernovas. The new maps should give astronomers a better chance of understanding the birth of the mysterious rays.
Cosmic rays are energetic particles that stream through the universe. Some slam into Earth's atmosphere, triggering a cascade of other particles detectable on the ground. A popular theory holds that cosmic rays are created in supernovas. But until now this has been difficult to prove. The rays must travel to Earth from distant parts of our galaxy, or even from other galaxies far away. Magnetic forces can deflect the rays during their trip through space, confusing our sense of their origin.

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Ultra-high energy cosmic rays
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Title: A High Rate of White Dwarf-Neutron Star Mergers & Their Transients
Authors: Todd A. Thompson, Matthew D. Kistler, K. Z. Stanek

We argue that the recent groundbreaking discovery by Badenes et al. (2009) of a nearby (~50 pc) white dwarf-neutron star (or black hole) binary (SDSS 1257+5428) with a merger timescale ~500 Myr implies that such systems are common; we estimate that there are of order 10^6 in the Galaxy. Although subject to large uncertainties, the nominal derived merger rate is ~5 x 10^-4 per yr in the Milky Way, just ~3-6 and ~20-40 times less than the Type Ia and core-collapse supernova (SN) rates, respectively. This implies that the merger rate is ~0.5-1 x 10^4 per Gpc^3 per yr in the local universe, ~5000-10000 times more than the observed (beaming-uncorrected) long-duration gamma-ray burst (GRB) rate. We estimate the lower limit on the rate in the Galaxy to be >2.5 x 10^-5 per yr at 95% confidence. We briefly discuss the implications of this finding for the census of long- and short-duration GRBs and their progenitors, the frequency of tight binary companions to Type Ib/c SN progenitors, the origin of ultra-high energy cosmic rays (UHECRs), the formation of rapidly rotating neutron stars and ~2-3 M_sun black holes, the census of faint Ia-like SNe, as well as for upcoming and current transient surveys (e.g., LOSS, PTF, LSST), and for high- (LIGO) and low-frequency (LISA) gravitational wave searches.

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Baby black holes are puny compared with their humongous cousins at the centres of galaxies, but their birth may spew out the universe's mightiest particles.
Subatomic particles are routinely detected smashing into Earth's atmosphere at incredibly high energies, but the origin of these ultra-high-energy cosmic rays (UHECRs) remains a mystery. Some have argued that energy released by the collapse of a massive single star to form a black hole might produce the UHECRs, but the rate of such events is too low.
Todd Thompson at Ohio State University in Columbus and his colleagues argue that UHECRs may instead originate in the merger of two types of dead star, which gives birth to a black hole.

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Starburst galaxy sheds light on longstanding cosmic mystery
An international collaboration that includes scientists from the University of Delaware's Bartol Research Institute in the Department of Physics and Astronomy has discovered very-high-energy gamma rays in the Cigar Galaxy (M82), a bright galaxy filled with exploding stars 12 million light years from Earth.
The gamma rays observed by the team have energies more than a trillion times higher than the energy of visible light and are the highest-energy photons ever detected from a galaxy undergoing large amounts of star formation.
The discovery, made from data taken over a two-year-long observing campaign by the VERITAS collaboration of more than 100 scientists from 22 different institutions in the United States, Ireland, United Kingdom, and Canada, appears in the Nov. 1 advance online edition of the scientific journal Nature.


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VERITAS Telescopes Help Solve 100-Year-Old Mystery: The Origin of Cosmic Rays
Nearly 100 years ago, scientists detected the first signs of cosmic rays - subatomic particles (mostly protons) that zip through space at nearly the speed of light. The most energetic cosmic rays hit with the punch of a 98-mph fastball, even though they are smaller than an atom. Astronomers questioned what natural force could accelerate particles to such a speed. New evidence from the VERITAS telescope array shows that cosmic rays likely are powered by exploding stars and stellar "winds."
These findings were published in the Nov. 1 online issue of the journal Nature, and are being featured today in a press conference at the Fermi Science Symposium in Washington, DC.

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Cosmic Rays Hit Space Age High
Planning a trip to Mars? Take plenty of shielding. According to sensors on NASA's ACE (Advanced Composition Explorer) spacecraft, galactic cosmic rays have just hit a Space Age high.

"In 2009, cosmic ray intensities have increased 19% beyond anything we've seen in the past 50 years. The increase is significant, and it could mean we need to re-think how much radiation shielding astronauts take with them on deep-space missions" - Richard Mewaldt of Caltech.

The cause of the surge is solar minimum, a deep lull in solar activity that began around 2007 and continues today. Researchers have long known that cosmic rays go up when solar activity goes down. Right now solar activity is as weak as it has been in modern times, setting the stage for what Mewaldt calls "a perfect storm of cosmic rays."

"We're experiencing the deepest solar minimum in nearly a century, so it is no surprise that cosmic rays are at record levels for the Space Age" - Dean Pesnell of the Goddard Space Flight Centre.

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Milky Way's super-efficient particle accelerators caught in the act
Thanks to a unique "ballistic study" that combines data from ESO's Very Large Telescope and NASA's Chandra X-ray Observatory, astronomers have now solved a long-standing mystery of the Milky Way's particle accelerators. They show that cosmic rays from our galaxy are very efficiently accelerated in the remnants of exploded stars.
During the Apollo flights astronauts reported seeing odd flashes of light, visible even with their eyes closed. We have since learnt that the cause was cosmic rays - extremely energetic particles from outside the Solar System arriving at the Earth, and constantly bombarding its atmosphere. Once they reach Earth, they still have sufficient energy to cause glitches in electronic components.
Galactic cosmic rays come from sources inside our home galaxy, the Milky Way, and consist mostly of protons moving at close to the speed of light, the "ultimate speed limit" in the Universe. These protons have been accelerated to energies exceeding by far the energies that even CERN's Large Hadron Collider will be able to achieve.

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Pierre Auger Observatory
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Radiation from the stars sheds "light" on universe
Did you know that Adelaide is playing a key role in a major international project that is changing the way we "see" the universe?
Astrophysicists from the University of Adelaide are among a group of scientists across the globe who are no longer using light to explore the deepest reaches of space.

"When most people think about 'looking at the stars', they think of using a traditional telescope to view space - that is, using light. But in the 21st century, new observatories are using high-energy particles of radiation to gain a much clearer picture of what's going on out there" - Professor Roger Clay, an astrophysicist with the University of Adelaide's School of Chemistry & Physics.

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