New images from NASA's Fermi Gamma-ray Space Telescope showing where supernova remnants emit radiation a billion times more energetic than visible light have brought astronomers a step closer to understanding the source of cosmic rays.
Cosmic rays consist mainly of protons that move through space at nearly the speed of light. In their journey across the galaxy, the particles are deflected by magnetic fields, which scrambles their paths and masks their origins.
"Understanding the sources of cosmic rays is one of Fermi's key goals," said Stefan Funk, an astrophysicist at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), jointly located at SLAC National Accelerator Laboratory and Stanford University, Calif. "Fermi now allows us to compare emission from remnants of different ages and in different environments."
This composite shows the Cassiopeia A supernova remnant across the spectrum: Gamma rays (magenta) from NASA's Fermi Gamma-ray Space Telescope; X-rays (blue, green) from NASA's Chandra X-ray Observatory; visible light (yellow) from the Hubble Space Telescope; infrared (red) from NASA's Spitzer Space Telescope; and radio (orange) from the Very Large Array near Socorro, N.M.
(Photo Credit: NASA/DOE/Fermi LAT Collaboration, CXC/SAO/JPL-Caltech/Steward/O. Krause et al., and NRAO/AUI)
Fermi's Large Area Telescope (LAT) mapped billion-electron-volt (GeV) gamma-rays from three middle-aged supernova remnants -- known as W51C, W44 and IC 443 -- that were never before resolved at these energies. (The energy of visible light is between 2 and 3 electron volts.) Each remnant is the expanding debris of a massive star that blew up between 4,000 and 30,000 years ago.
In addition, Fermi's LAT also spied GeV gamma rays from Cassiopeia A (Cas A), a supernova remnant only 330 years old. Ground-based observatories, which detect gamma rays thousands of times more energetic than the LAT was designed to see, have previously detected Cas A.
"Older remnants are extremely bright in GeV gamma rays, but relatively faint at higher energies. Younger remnants show a different behavior," explained Yasunobu Uchiyama, a Panofsky Fellow at SLAC. "Perhaps the highest-energy cosmic rays have left older remnants, and Fermi sees emission from trapped particles at lower energies."
In 1949, the Fermi telescope's namesake, physicist Enrico Fermi, suggested that the highest-energy cosmic rays were accelerated in the magnetic fields of gas clouds. In the decades that followed, astronomers showed that supernova remnants are the galaxy's best candidate sites for this process.
Young supernova remnants seem to possess both stronger magnetic fields and the highest-energy cosmic rays. Stronger fields can keep the highest-energy particles in the remnant's shock wave long enough to speed them to the energies observed.
The Fermi observations show GeV gamma rays coming from places where the remnants are known to be interacting with cold, dense gas clouds.
"We think that protons accelerated in the remnant are colliding with gas atoms, causing the gamma-ray emission," Funk said. An alternative explanation is that fast-moving electrons emit gamma rays as they fly past the nuclei of gas atoms. "For now, we can't distinguish between these possibilities, but we expect that further observations with Fermi will help us to do so," he added.
Either way, these observations validate the notion that supernova remnants act as enormous accelerators for cosmic particles.
"How fitting it is that Fermi seems to be confirming the bold idea advanced over 60 years ago by the scientist after whom it was named," noted Roger Blandford, director of KIPAC.
- PHYSICAL SCIENCES
- EARTH SCIENCES
- LIFE SCIENCES
- SOCIAL SCIENCES
Subscribe to the newsletter
Stay in touch with the scientific world!
Know Science And Want To Write?
- What Lies Beneath West Antarctica?
- The Genetic History Of Ice Age Europe
- Exodus 2100: Due To Climate Change
- New Interpretation Of The Rök Runestone Inscription Changes View Of Viking Age
- Race And Racism 101 Lecture 1 Intro & Terminology
- Professor Frenkel: Why Shouldn't We Drop Algebra From Our Education System?
- Three Earth-sized Planets Found Orbiting A Tiny Nearby Star
- "Phew! Finally!! Trouble is, you have to have an IQ of well over 100 to understand it. PLUS, you..."
- "Top US scientist Hal Lewis resigned from his post at the University of California after admitting..."
- " Hilarious! ..."
- " Warning! Warning! Warning! elfish is a privileged troll living for an ivory tower! http://plato..."
- "This is a decent article and I think the journalist did a good job of avoiding the usual exaggerations..."
- One third of antibiotic prescriptions unnecessary
- UC San Diego bioengineers create first online search engine for functional genomics data
- UK Health Check has only modest impact on risk factors for cardiovascular disease
- Adult brain prunes branched connections of new neurons
- Five new breast cancer genes and range of mutations pave way for personalized treatment