ESO: Clues to the Mysterious Origin of Cosmic Rays

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ESO: Clues to the Mysterious Origin of Cosmic Rays

Post by bystander » Fri Feb 15, 2013 6:25 pm

Clues to the Mysterious Origin of Cosmic Rays
European Southern Observatory | VLT | 2013 Feb 14

VLT probes remains of medieval supernova
Very detailed new observations with ESO’s Very Large Telescope (VLT) of the remains of a thousand-year-old supernova have revealed clues to the origins of cosmic rays. For the first time the observations suggest the presence of fast-moving particles in the supernova remnant that could be the precursors of such cosmic rays. The results are appearing in the 14 February 2013 issue of the journal Science.

In the year 1006 a new star was seen in the southern skies and widely recorded around the world. It was many times brighter than the planet Venus and may even have rivaled the brightness of the Moon. It was so bright at maximum that it cast shadows and it was visible during the day. More recently astronomers have identified the site of this supernova and named it SN 1006. They have also found a glowing and expanding ring of material in the southern constellation of Lupus (The Wolf) that constitutes the remains of the vast explosion.

It has long been suspected that such supernova remnants may also be where some cosmic rays — very high energy particles originating outside the Solar System and travelling at close to the speed of light — are formed. But until now the details of how this might happen have been a long-standing mystery.

A team of astronomers led by Sladjana Nikolić (Max Planck Institute for Astronomy, Heidelberg, Germany) has now used the VIMOS instrument on the VLT to look at the one-thousand-year-old SN 1006 remnant in more detail than ever before. They wanted to study what is happening where high-speed material ejected by the supernova is ploughing into the stationary interstellar matter — the shock front. This expanding high-velocity shock front is similar to the sonic boom produced by an aircraft going supersonic and is a natural candidate for a cosmic particle accelerator.

For the first time the team has not just obtained information about the shock material at one point, but also built up a map of the properties of the gas, and how these properties change across the shock front. This has provided vital clues to the mystery.

The results were a surprise — they suggest that there were many very rapidly moving protons in the gas in the shock region. While these are not the sought-for high-energy cosmic rays themselves, they could be the necessary “seed particles”, which then go on to interact with the shock front material to reach the extremely high energies required and fly off into space as cosmic rays.

Nikolić explains: “This is the first time we were able to take a detailed look at what is happening in and around a supernova shock front. We found evidence that there is a region that is being heated in just the way one would expect if there were protons carrying away energy from directly behind the shock front.”

The study was the first to use an integral field spectrograph to probe the properties of the shock fronts of supernova remnants in such detail. The team now is keen to apply this method to other remnants.

Co-author Glenn van de Ven of the Max Planck Institute for Astronomy, concludes: “This kind of novel observational approach could well be the key to solving the puzzle of how cosmic rays are produced in supernova remnants.”

Novel approach in hunt for cosmic particle accelerator
Max Planck Institute for Astronomy | 2013 Feb 14

An Integral View of Fast Shocks Around Supernova 1006 - Sladjana Nikolić et al
Confirmed: Cosmic Rays Come From Exploding Stars
Discover Blogs | 80beats | Bill Andrews | 2013 Feb 15
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

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NASA: Fermi Proves Supernova Remnants Produce Cosmic Rays

Post by bystander » Fri Feb 15, 2013 6:51 pm

Fermi Proves Supernova Remnants Produce Cosmic Rays
NASA | GSFC | Fermi | 2013 Feb 14
Click to play embedded YouTube video.

A new study using observations from NASA's Fermi Gamma-ray Space Telescope reveals the first clear-cut evidence the expanding debris of exploded stars produces some of the fastest-moving matter in the universe. This discovery is a major step toward understanding the origin of cosmic rays, one of Fermi's primary mission goals.

"Scientists have been trying to find the sources of high-energy cosmic rays since their discovery a century ago," said Elizabeth Hays, a member of the research team and Fermi deputy project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "Now we have conclusive proof supernova remnants, long the prime suspects, really do accelerate cosmic rays to incredible speeds."

Cosmic rays are subatomic particles that move through space at almost the speed of light. About 90 percent of them are protons, with the remainder consisting of electrons and atomic nuclei. In their journey across the galaxy, the electrically charged particles are deflected by magnetic fields. This scrambles their paths and makes it impossible to trace their origins directly.

Through a variety of mechanisms, these speedy particles can lead to the emission of gamma rays, the most powerful form of light and a signal that travels to us directly from its sources.

Since its launch in 2008, Fermi's Large Area Telescope (LAT) has mapped million- to billion-electron-volt (MeV to GeV) gamma-rays from supernova remnants. For comparison, the energy of visible light is between 2 and 3 electron volts.

The Fermi results concern two particular supernova remnants, known as IC 443 and W44, which scientists studied to prove supernova remnants produce cosmic rays. IC 443 and W44 are expanding into cold, dense clouds of interstellar gas. These clouds emit gamma rays when struck by high-speed particles escaping the remnants.

Scientists previously could not determine which atomic particles are responsible for emissions from the interstellar gas clouds because cosmic ray protons and electrons give rise to gamma rays with similar energies. After analyzing four years of data, Fermi scientists see a distinguishable feature in the gamma-ray emission of both remnants. The feature is caused by a short-lived particle called a neutral pion, which is produced when cosmic ray protons smash into normal protons. The pion quickly decays into a pair of gamma rays, emission that exhibits a swift and characteristic decline at lower energies. The low-end cutoff acts as a fingerprint, providing clear proof that the culprits in IC 443 and W44 are protons.

The findings will appear in Friday's issue of the journal Science.

"The discovery is the smoking gun that these two supernova remnants are producing accelerated protons," said lead researcher Stefan Funk, an astrophysicist with the Kavli Institute for Particle Astrophysics and Cosmology at Stanford University in Calif. "Now we can work to better understand how they manage this feat and determine if the process is common to all remnants where we see gamma-ray emission."

In 1949, the Fermi telescope's namesake, physicist Enrico Fermi, suggested the highest-energy cosmic rays were accelerated in the magnetic fields of interstellar gas clouds. In the decades that followed, astronomers showed supernova remnants were the galaxy's best candidate sites for this process.

A charged particle trapped in a supernova remnant's magnetic field moves randomly throughout the field and occasionally crosses through the explosion's leading shock wave. Each round trip through the shock ramps up the particle's speed by about 1 percent. After many crossings, the particle obtains enough energy to break free and escape into the galaxy as a newborn cosmic ray.

The supernova remnant IC 443, popularly known as the Jellyfish Nebula, is located 5,000 light-years away toward the constellation Gemini and is thought to be about 10,000 years old. W44 lies about 9,500 light-years away toward the constellation Aquila and is estimated to be 20,000 years old. Each is the expanding shock wave and debris formed when a massive star exploded.

The Fermi discovery builds on a strong hint of neutral pion decay in W44 observed by the Italian Space Agency's AGILE gamma ray observatory and published in late 2011.

Cosmic Rays Come from Exploding Stars
Stanford University | SLAC | 2013 Feb 14

Accelerated protons confirm origin of cosmic rays
AAAS | via EurekAlert | 2013 Feb 14

Source of High-Energy Cosmic Rays Nailed at Last
Science NOW | Daniel Clery | 2013 Feb 14

Detection of the Characteristic Pion-Decay Signature in Supernova Remnants - M. Ackermann et al
Supernovae Seed Universe With Cosmic Rays
Universe Today | Tammy Plotner | 2013 Feb 15
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

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