Sunday, 24 February 2013

NASA confirms the origin of cosmic rays

A multiwavelength composite image of supernova remnant IC 443, known as the Jellyfish Nebu... Hi Friends,
The study of data collected by NASA's Fermi Gamma-ray Space Telescope has revealed that cosmic rays, some of the fastest traveling particles in the universe, are produced by supernovae. A separate study by the European Southern Observatory (ESO) has made similar findings, largely corroborating the Fermi results.
Cosmic rays are subatomic particles, made up of around ninety percent protons, that move through space at close to the speed of light. Magnetic fields deflect and distort the path of the particles, making it near impossible to determine their point of origin. However, the presence of cosmic rays
can, under certain circumstances, lead to the emission of gamma rays, a form of light that travels to us directly from its source.
NASA's Fermi Large Area Telescope (LAT) has been observing these gamma rays since its launch in 2008, focusing on two supernova remnants known as IC443 and W44. Both of these are expanding into clouds of interstellar dust which emit gamma-rays when hit by high-speed particles from the supernova remnants.
The W44 supernova remnant
The W44 supernova remnant
After analyzing four years' worth of data, the team has managed to identify a feature in the gamma rays of both IC443 and W44, which is claimed to constitute conclusive proof that supernova remnants accelerate cosmic rays. The scientists identified the presence of particles known as neutral pions, which are created in collisions between cosmic rays and normal protons. These neutral pions break down into pairs of gamma rays and exhibit specific and identifiable characteristics.
Stefan Funk of the Kavli Institute for Particle Astrophysics and Cosmology at Stanford University said that "the discovery is the smoking gun that these two supernova remnants are producing accelerated protons."
The thousand-year-old SN1006 supernova remnant
The thousand-year-old SN1006 supernova remnant
An ESO study, released simultaneously to the Fermi findings, largely corroborated the discovery. The ESO team used its Very Large Telescope (VLT) to observe a supernova site known as SN 1006, focusing on the “shock front” where high-speed materials ejected by the supernova interact with stationary interstellar matter.
While the team was unable to confirm the existence of cosmic rays, a number of “seed particles” were identified. These particles go on to interact with other materials, eventually reaching the extremely high energy levels associated with cosmic rays.