Discovered: Cosmic Rays from a Mysterious, Nearby Object
Nov. 19, 2008: An international team of researchers has discovered a puzzling surplus of high-energy electrons bombarding Earth from space. The source of these cosmic rays is unknown, but it must be close to the solar system and it could be made of dark matter. Their results are being reported in the Nov. 20th issue of the journal Nature.
"This is a big discovery," says co-author John Wefel of Louisiana State University. "It's the first time we've seen a discrete source of accelerated cosmic rays standing out from the general galactic background."
Galactic cosmic rays are subatomic particles accelerated to almost light speed by distant supernova explosions and other violent events. They swarm through the Milky Way, forming a haze of high energy particles that enter the solar system from all directions. Cosmic rays consist mostly of protons and heavier atomic nuclei with a dash of electrons and photons spicing the mix.
To study the most powerful and interesting cosmic rays, Wefel and colleagues have spent the last eight years flying a series of balloons through the stratosphere over Antarctica. Each time the payload was a NASA-funded cosmic ray detector named ATIC, short for Advanced Thin Ionization Calorimeter. The team expected ATIC to tally the usual mix of particles, mainly protons and ions, but the calorimeter found something extra: an abundance of high-energy electrons.
Wefel likens it to driving down a freeway among family sedans, mini-vans and trucks—when suddenly a bunch of Lamborghinis bursts through the normal traffic. "You don't expect to see so many race cars on the road—or so many high-energy electrons in the mix of cosmic rays." During five weeks of ballooning in 2000 and 2003, ATIC counted 70 excess electrons in the energy range 300-800 GeV. ("Excess" means over and above the usual number expected from the galactic background.) Seventy electrons may not sound like a great number, but like seventy Lamborghinis on the freeway, it's a significant surplus.
"This is a big discovery," says co-author John Wefel of Louisiana State University. "It's the first time we've seen a discrete source of accelerated cosmic rays standing out from the general galactic background."
Galactic cosmic rays are subatomic particles accelerated to almost light speed by distant supernova explosions and other violent events. They swarm through the Milky Way, forming a haze of high energy particles that enter the solar system from all directions. Cosmic rays consist mostly of protons and heavier atomic nuclei with a dash of electrons and photons spicing the mix.
To study the most powerful and interesting cosmic rays, Wefel and colleagues have spent the last eight years flying a series of balloons through the stratosphere over Antarctica. Each time the payload was a NASA-funded cosmic ray detector named ATIC, short for Advanced Thin Ionization Calorimeter. The team expected ATIC to tally the usual mix of particles, mainly protons and ions, but the calorimeter found something extra: an abundance of high-energy electrons.
Wefel likens it to driving down a freeway among family sedans, mini-vans and trucks—when suddenly a bunch of Lamborghinis bursts through the normal traffic. "You don't expect to see so many race cars on the road—or so many high-energy electrons in the mix of cosmic rays." During five weeks of ballooning in 2000 and 2003, ATIC counted 70 excess electrons in the energy range 300-800 GeV. ("Excess" means over and above the usual number expected from the galactic background.) Seventy electrons may not sound like a great number, but like seventy Lamborghinis on the freeway, it's a significant surplus.
Comments
Post a Comment