Cosmic gamma rays - Astronomy News

Blobrana

L

Posts: 131433

Date: Nov 8 19:41 2007

Ultra high-energy cosmic rays	Permalink

Black holes are the most likely source of the mysterious ultra high-energy cosmic rays that bombard the planet, scientists have discovered. Observations at the world's largest cosmic ray detector suggest the particles are emitted by huge black holes in the middle of nearby galaxies. The findings, unveiled in Science, may solve a long-running puzzle. The origins of the highest energy forms of cosmic rays have been a mystery since their discovery in 1912. The observations were made by more than 370 scientists from 17 countries working at the Pierre Auger Observatory in Argentina. Read more __________________

Blobrana

L

Posts: 131433

Date: Oct 22 21:16 2007

Ultra-high-energy cosmic rays	Permalink

Vast magnetic cocoons associated with galaxies whose black holes have stopped eating may be responsible for accelerating charged particles called cosmic rays to within a whisker of the speed of light. It could explain one of the great mysteries of astrophysics how enormously energetic cosmic rays make it to Earth, when common sense says they should long ago have run out of steam. Cosmic rays are high-speed atomic nuclei, most commonly of hydrogen. Most come from objects within our galaxy, such as supernova remnants and pulsars. But ultra-high-energy cosmic rays (UHECRs) each packing the punch of a baseball are an outstanding mystery. Although it is conceivable that they are produced near the Milky Way by the decay of super-heavy dark matter particles or by defects in space-time, the most likely sources are the most powerful objects in the universe 'active' galaxies whose colossal black holes are devouring nearby matter, and gamma-ray bursts. These are far beyond our galaxy and herein lies a very serious problem. Read more __________________

Blobrana

L

Posts: 131433

Date: Oct 13 20:51 2007

RE: Cosmic gamma rays	Permalink

An international team of astronomers has produced the first ever image of an astronomical object using high energy gamma rays, helping to solve a 100 year old mystery - an origin of cosmic rays. The astronomers studied the remnant of a supernova that exploded some 1,000 years ago, leaving behind an expanding shell of debris which, seen from the Earth, is twice the diameter of the Moon. The resulting image helps to solve a mystery that has been puzzling scientists for almost 100 years - the origin of cosmic rays. Cosmic rays are extremely energetic particles that continually bombard the Earth, thousands of them passing through our bodies every day. Source __________________

Blobrana

L

Posts: 131433

Date: Oct 11 19:34 2007

Cosmic rays	Permalink

Recent observations from NASA and Japanese X-ray observatories have helped clarify one of the long-standing mysteries in astronomy -- the origin of cosmic rays. Outer space is a vast shooting gallery of cosmic rays. Discovered in 1912, cosmic rays are not actually rays at all; they are subatomic particles and ions (such as protons and electrons) that zip through space in all directions at near-light speed, with energies tens of thousands of times greater than particles produced in Earths largest particle accelerators. Cosmic rays incessantly bombard Earth, smashing into the atoms and molecules high up in the atmosphere, and producing cascades of secondary particles that reach the surface. Since the 1960s scientists have pointed to supernova remnants -- the tattered, gaseous remains of supernovae -- as the breeding ground of most cosmic rays. These remnants expand into the surrounding interstellar gas, an energetic interaction that produces a shock front containing magnetic fields that can accelerate charged particles to enormous energies, producing cosmic rays. According to theory, charged subatomic particles bounce like pinballs around the shock front. They pick up speed until they move nearly the speed of light. Last year, observations from NASAs Chandra X-ray Observatory suggested that electrons are being accelerated rapidly (as fast as theory allows) to high energies in the supernova remnant Cassiopeia A. Expand (2.44mb, 2372 X 1836) These images from NASA's Chandra X-ray Observatory show small portions of an edge of RXJ1713.7-3946. The small images on the right show hot spots appearing and disappearing. The rapid rise and fall of the spots indicate that electrons are being accelerated to near-light speed in the presence of strong magnetic fields. Click image for unlabeled version. Credit: CXC/Yasunobu Uchiyama/HESS/Nature Read more __________________

Blobrana

L

Posts: 131433

Date: Aug 14 12:12 2007

UHECRs	Permalink

Title: Evidence that a cluster of UHECRs was produced by a burst or flare Authors: Glennys R. Farrar The angular clustering of 5 Ultrahigh Energy Cosmic Rays (UHECRs) in the combined published AGASA-HiRes data has a probability of ~ 2 10^-3 of occurring by chance. A first analysis of the implications of the event energies and angular spreading is presented, which is applicable if the source is close enough that GZK losses can be ignored. Under this assumption, the observed energies of the events in this cluster favour a bursting rather than continuously emitting source, with the events emitted on a time scale short compared with 300 D_Mpc years. Assuming the UHECRs experience many incoherent small magnetic deflections enroute from source to Earth, the arrival direction distribution allows estimation that < B² lambda > D ~ 7.7 nG² Mpc², where lambda is the coherence length of the field and D is the source distance. If the spectrum at the source ~ E^{-2}, the total isotropic equivalent energy emitted in UHECRs is > 10^43 D_Mpc³ ergs. Read more (24kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Jul 4 03:03 2007

Highest energy cosmic rays	Permalink

An otherwise inexplicable excess in the highest energy cosmic rays crashing into Earth has been explained in the simplest way: The excess simply doesn't exist. The new result may disappoint physicists who had perceived hints of exciting new phenomena in the overabundance of individual subatomic particles cruising along with as much energy as a large hailstone. It also leaves some mysteries unanswered. Really energetic particles should hit Earth only very rarely. After all, the number of cosmic rays pelting Earth decreases steadily as the energy of the rays increases. Above a specific energy, the rate ought to drop even faster. For example, if the rays consist mainly of protons, then at such tremendous energies they ought to break into other subatomic particles when they collide with photons in the afterglow of the big bang, the cosmic microwave background. That effect is known as the GKZ cutoff and it should limit the energy of cosmic rays to about 10^18 electron volts, a million times the energy achieved with particle accelerators. But from 1990 to 2004, physicists working with the Akeno Giant Air Shower Array (AGASA) west of Tokyo spotted roughly a dozen particles with energies 100 times higher. That excess puzzled physicists, both because they could not explain how the rays got past the GZK cutoff or how they could gain so much energy in the first place. Now, a new gigantic cosmic ray detector that employs both techniques has settled the issue. The almost-completed Pierre Auger Observatory on the plains of the Pampa Amarilla in western Argentina comprises more than 1200 ground detectors and 24 telescopes and covers an area of 300 square kilometers. And the array has already collected enough data to rule out an excess in cosmic rays above 10²⁰ eV. Source __________________

Blobrana

L

Posts: 131433

Date: Mar 24 21:05 2007

Cosmic gamma rays	Permalink

In 2002, when astronomers first detected cosmic gamma rays — the most energetic form of light known — coming from the constellation Cygnus they were surprised and perplexed. The region lacked the extreme electromagnetic fields that they thought were required to produce such energetic rays. But now a team of theoretical physicists propose a mechanism that can explain this mystery and may also help account for another type of cosmic ray, the high-energy nuclei that rain down on Earth in the billions. The new mechanism is described in a Physical Review Letters paper published online on March 20. The theoretical study was headed by Thomas Weiler, professor of physics at Vanderbilt, working with Luis Anchordoqui at the University of Wisconsin-Milwaukee; John Beacom at Ohio State University; Haim Goldberg at Northeastern University; and Sergio Palomares-Ruiz at the University of Durham. Existing methods for producing cosmic gamma rays require the ultra-strong electromagnetic fields found only in some of the most extreme conditions in the universe, such as stellar explosions and regions surrounding the massive black holes found at the core of many galaxies. So they couldn't explain how a "starburst" region in the Cygnus galaxy dominated by young, hot, bright stars could produce such energetic rays. The newly proposed mechanism, however, shows how two constituents present in such an area — fast-moving nuclei found in stellar winds and ultraviolet light — can interact to produce cosmic gamma rays. Cosmic rays provide an invisible but important link between the Earth and the rest of the universe. They have a number of subtle effects on everyday life. They cause chemical changes in soil and rock and trigger lightning strikes, and some scientists have suggested that they may affect the climate by influencing the process of cloud formation. The circuitry in computer chips is now so small that individual cosmic rays can cause non-reproducible computer errors, and cosmic rays increase the risk of cancer among frequent airline passengers. There is also speculation that waves of cosmic rays streaming down the spiral arms of the galaxy could have contributed to past episodes of mass extinction on earth. Read more __________________

* Astronomy