Where do cosmic rays come from?
Where do osmic rays come from?
After the discovery of radiation by French physicist Henri Becquerel (1852-1908) in 1896, scientists believed atmospheric ionization (where an electron is stripped from an air
molecule) occurred only from radioactive Hess (1883-1964) found an additional elements found in ground rocks or from source in 1912, when he strapped three
radioactive gases. Austrian physicist Victor electrometers into a balloon and measured
atmospheric radiation at an altitude of about 15,000 feet (4,600 meters).
He found an ionization rate about 4 times greater than at ground level. Hess could explain the variant observations only if a powerful source of radiation were penetrating the atmosphere from above. Much later, in 1936, Hess received the Nobel Prize
44 50 GREATEST MYSTERIES
HEAVY BOOM. A massive supernova remnant,
N63A, marks the site of a blast of cosmic rays that occurred when a star 50 times more massive than the Sun ended its life, nasa/esa/
HEIOTHE HUBBLE HERITAGE TEAM
in physics for the discovery of what we now call cosmic rays.
Physicists initially believed cosmic rays were gamma rays, high-energy radiation produced by radioactive decay. During the 1930s, however, experiments revealed that cosmic rays are mostly charged particles. In 1937, French physicist Pierre Auger (1899-1993) found that extensive particle showers (called air showers) occur when cosmic rays collide with particles high in the atmosphere, producing a cascade of electrons, photons, and muons (particles similar to electrons but 200 times as massive) that reach Earth's surface.
In 1954, members of the Rossi Cosmic X- ray Group at the Massachusetts Institute of Technology in Cambridge made the first samplings of extensive air showers. The network of detectors at Harvard College Observatory produced much data on cosmic rays and their levels of energy.
In Argentina, the Pierre Auger Observatory opened in 2003 and aims to detect extremely high-energy cosmic rays.This international project will include a northern component in southeastern Colorado. The particles under detection have as much energy as a tennis ball traveling at 340 mph (550 km/h), packed into the space of a single proton. Physicists have nicknamed them "Oh-my-God particles."
Aside from the Auger Observatory, other cosmic-ray research projects include HiRes at the University of Utah; MARIACHl, a project of the National Science Foundation, Stony Brook University, and Brookhaven National Laboratory; and SLAC, at the Stanford Linear Accelerator.
When the particles produced in air showers decay, three kinds of neutrinos result. Because neutrinos so rarely interact with other matter, most pass through Earth undetected. But ambitious detector projects now in operation are searching for neutrinos
produced by cosmic-ray showers. In 1998, the Super-Kamiokande detector in Japan found evidence of one type of neutrino changing into another "flavor."
By studying cosmic rays for several decades now, astronomers have begun to understand them.
Astronomers categorize cosmic rays into four basic types. The first are those with low energies, called anomalous cosmic rays. They probably originate in the heliosheath, at the solar system's edge, where the solar wind no longer has any effect. Astronomers believe anomalous cosmic rays occur when electrically neutral atoms in the heliosheath are ionized and accelerated. However, when the Voyager 1 spacecraft passed into the inner edge of the heliosheath, it did not detect any such particle acceleration. So the jury is still out.
The second type, galactic cosmic rays, flows into the solar system from other parts of the Milky Way. Astronomers believe supernovae produce most cosmic rays of this type. In the aftermath of a supernova explosion, particles bounce repeatedly within the gaseous remnant and accelerate into cosmic rays. At some critical point, they escape into the galaxy.
Third are the abundant cosmic rays that originate from the Sun. Most of these are
9 *
LOCAL STREAM. The Sun produces a stream of cosmic rays that constantly bombards our planet. This Extreme Ultraviolet Imaging Telescope photo, made with the SOHO spacecraft February 17, 2001, shows a huge loop prominence at upper right.
protons, particles at relatively low energies. The intense magnetic fields at the Sun's surface energize them.
The last kind are ultrahigh-energy cosmic rays, the type being sought by the Auger
Observatory and other projects.These include the Oh-my-God particles. Scientists don't yet know these particles' origins, although researchers plan a number of experiments to try to understand them.03
DARK AND MURKY. The interstellar medium, gas and dust between the stars, produces cosmic rays that reach Earth. A pillar of gas and dust in the Eagle Nebula (M16) reveals the rich structure of the stuff that fills our galaxy.
SOHO
After the discovery of radiation by French physicist Henri Becquerel (1852-1908) in 1896, scientists believed atmospheric ionization (where an electron is stripped from an air
molecule) occurred only from radioactive Hess (1883-1964) found an additional elements found in ground rocks or from source in 1912, when he strapped three
radioactive gases. Austrian physicist Victor electrometers into a balloon and measured
atmospheric radiation at an altitude of about 15,000 feet (4,600 meters).
He found an ionization rate about 4 times greater than at ground level. Hess could explain the variant observations only if a powerful source of radiation were penetrating the atmosphere from above. Much later, in 1936, Hess received the Nobel Prize
44 50 GREATEST MYSTERIES
HEAVY BOOM. A massive supernova remnant,
N63A, marks the site of a blast of cosmic rays that occurred when a star 50 times more massive than the Sun ended its life, nasa/esa/
HEIOTHE HUBBLE HERITAGE TEAM
in physics for the discovery of what we now call cosmic rays.
Physicists initially believed cosmic rays were gamma rays, high-energy radiation produced by radioactive decay. During the 1930s, however, experiments revealed that cosmic rays are mostly charged particles. In 1937, French physicist Pierre Auger (1899-1993) found that extensive particle showers (called air showers) occur when cosmic rays collide with particles high in the atmosphere, producing a cascade of electrons, photons, and muons (particles similar to electrons but 200 times as massive) that reach Earth's surface.
In 1954, members of the Rossi Cosmic X- ray Group at the Massachusetts Institute of Technology in Cambridge made the first samplings of extensive air showers. The network of detectors at Harvard College Observatory produced much data on cosmic rays and their levels of energy.
In Argentina, the Pierre Auger Observatory opened in 2003 and aims to detect extremely high-energy cosmic rays.This international project will include a northern component in southeastern Colorado. The particles under detection have as much energy as a tennis ball traveling at 340 mph (550 km/h), packed into the space of a single proton. Physicists have nicknamed them "Oh-my-God particles."
Aside from the Auger Observatory, other cosmic-ray research projects include HiRes at the University of Utah; MARIACHl, a project of the National Science Foundation, Stony Brook University, and Brookhaven National Laboratory; and SLAC, at the Stanford Linear Accelerator.
When the particles produced in air showers decay, three kinds of neutrinos result. Because neutrinos so rarely interact with other matter, most pass through Earth undetected. But ambitious detector projects now in operation are searching for neutrinos
produced by cosmic-ray showers. In 1998, the Super-Kamiokande detector in Japan found evidence of one type of neutrino changing into another "flavor."
By studying cosmic rays for several decades now, astronomers have begun to understand them.
Astronomers categorize cosmic rays into four basic types. The first are those with low energies, called anomalous cosmic rays. They probably originate in the heliosheath, at the solar system's edge, where the solar wind no longer has any effect. Astronomers believe anomalous cosmic rays occur when electrically neutral atoms in the heliosheath are ionized and accelerated. However, when the Voyager 1 spacecraft passed into the inner edge of the heliosheath, it did not detect any such particle acceleration. So the jury is still out.
The second type, galactic cosmic rays, flows into the solar system from other parts of the Milky Way. Astronomers believe supernovae produce most cosmic rays of this type. In the aftermath of a supernova explosion, particles bounce repeatedly within the gaseous remnant and accelerate into cosmic rays. At some critical point, they escape into the galaxy.
Third are the abundant cosmic rays that originate from the Sun. Most of these are
9 *
LOCAL STREAM. The Sun produces a stream of cosmic rays that constantly bombards our planet. This Extreme Ultraviolet Imaging Telescope photo, made with the SOHO spacecraft February 17, 2001, shows a huge loop prominence at upper right.
protons, particles at relatively low energies. The intense magnetic fields at the Sun's surface energize them.
The last kind are ultrahigh-energy cosmic rays, the type being sought by the Auger
Observatory and other projects.These include the Oh-my-God particles. Scientists don't yet know these particles' origins, although researchers plan a number of experiments to try to understand them.03
DARK AND MURKY. The interstellar medium, gas and dust between the stars, produces cosmic rays that reach Earth. A pillar of gas and dust in the Eagle Nebula (M16) reveals the rich structure of the stuff that fills our galaxy.
SOHO
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