Where do cosmic rays come from?
Auger Observatory closes in on long-standing mystery, links highest-energy cosmic rays with violent black holes MALARGUE, Argentina — Scientists of the Pierre Auger Collaboration announced today (Nov. 8) that active galactic nuclei are the most likely candidate for the source of the highest-energy cosmic rays that hit Earth. Using the Pierre Auger Observatory in Argentina, the largest cosmic-ray observatory in the world, a team of scientists from 17 countries found that the sources of the highest-energy particles are not distributed uniformly across the sky. Instead, the Auger results link the origins of these mysterious particles to the locations of nearby galaxies that have active nuclei in their centers. The results will appear in the Nov. 9 issue of the journal Science. Active Galactic Nuclei (AGN) are thought to be powered by supermassive black holes that are devouring large amounts of matter. They have long been considered sites where high-energy particle production might take p
Scientists have been trying to answer that question since 1912, when Victor Hess discovered the mysterious particles during a high altitude balloon flight over Europe. Galactic cosmic rays shower our planet from all directions. There’s no definite source astronomers can pinpoint, although there is a popular candidate. Sign up for EXPRESS SCIENCE NEWS delivery “Most researchers are betting that cosmic rays come from supernova explosions,” says Jim Adams of the NASA/Marshall Space Flight Center. When massive stars explode they blast their own atmospheres into space. The expanding shock waves can break apart interstellar atoms and accelerate the debris to cosmic ray energies. Cosmic rays are subsequently scattered by interstellar magnetic fields — they wander through the Galaxy, losing their sense of direction as they go. “It takes an awful lot of power to maintain the galactic population of cosmic rays,” says Adams. “Cosmic rays that lose their energy or leak out of the Galaxy have to b
A major step toward answering this century old question may have just come in from the Auger Observatory project, the world’s premier cosmic ray observatory. That high energy fundamental particles are barreling through the universe has been known for about a century. Because ultra high energy cosmic rays are so rare and because their extrapolated directions are so imprecise, no progenitor objects have ever been unambiguously implied. New results from Auger, however, indicate that 12 of 15 ultra high energy cosmic rays have sky directions statistically consistent with the positions of nearby active galactic nuclei. These galactic centers are already known to emit great amounts of light and are likely powered by large black holes. The Auger results also indicate that the highest energy cosmic rays are protons, since the electric charge of higher energy nuclei would force the Milky Way Galaxy’s magnetic field to deflect and effectively erase progenitor source direction. Pictured above, an
All the light and the heat which we receive on the Earth comes from the sun, so it might seem a reasonable guess to suspect that cosmic rays may also come from the sun. This however is not the case. There are two bits of experimental evidence which backs up this statement. Firstly it is well known that during the day it is light and at night it is dark, in other words a variation of light intensity seen on Earth occurs during a day (24 hour cycle). Similarly the hottest part of the day occurs between 11am and 3pm, the coolest part occurring in the early hours of the morning. In other words there is a heat variation during the day. Based on these facts, it is reasonable to assume that if cosmic rays came from the sun, they too would have some daily variation in intensity. For example the intensity of cosmic rays received by the Earth would be large around lunchtime, and much less in the middle of the night. However no such variation is observed. Indeed the cosmic rays received by the Ea
