Particles that bombard the Earth from
anywhere beyond its atmosphere are known as
cosmic rays. Cosmic rays don't take pretty pictures, but studying the quantity and type of these particles helps us to understand the
acceleration processes involved and to measure the
composition of the Sun, as well as sources at the far distant reaches of the galaxy.
Cosmic rays include:
The relative numbers of different
isotopes found in the galaxy are established by the life cycle of massive stars. Star formation, evolution and explosion results in the creation of many of the heavier isotopes found in space. The process is shown in the figure below.
This stellar evolution image is courtesy of Drs. R. Mewaldt, E. Stone, and M. Wiedenbeck of the California Institute of Technology (Caltech).
In a part of the galaxy where the composition of the interstellar gas is much like that of our own solar system (a), a cloud of gas collapses under the influence of its own gravity, and creates a new star (b). Inside the star (c), fusion converts some of the original hydrogen and helium into particles like carbon-12 and oxygen-16. At the same time, the carbon, nitrogen, and oxygen nuclei that were originally present in the star's fuel are converted into heavier, neutron-rich nuclei, like neon-22 and magnesium-25.
When this burning has exhausted all of the nuclear fuel in the core of the star, the star explodes as a supernova (d). The shock wave generated by the explosion produces additional heavy nuclei and ejects most of these products of nucleosynthesis back into the interstellar gas.
Repetition of these events in each generation of stars steadily enriches the interstellar gas in carbon, nitrogen, and oxygen, and in heavy nuclei with an excess of neutrons.
Some of the nuclei in the gas are accelerated to cosmic ray speeds, possibly by the shock waves from supernovae (e). Cosmic ray acceleration could also occur directly as the supernova is ejecting matter into interstellar space, as in (d).
To learn a lot more about cosmic rays, energetic particles, and plasma, check out our question and answer page on cosmic rays in our "Ask Us" feature.
Even more about cosmic rays:
More about the interstellar medium:
April 23, 2012: Seeing
cosmic rays in space -- Astrobiology
February 10, 2012: Alien
matter in the solar system: A galactic mismatch -- Science@NASA
February 8, 2012: NASA
small explorer mission celebrates ten years and forty thousand x-ray
flares -- NASA
February 4, 2012: IBEX
glimpses alien interstellar material -- Astrobiology
February 1, 2012: A
century of cosmic rays -- Physics Today
January 2, 2012: How
cosmic rays can image the throat of an active volcano --
Scientific American
December 14, 2011: Curiosity
and the solar storm -- NASA
November 23, 2011: Measuring
the radiation on Mars -- Astrobiology
August 24, 2011: Cloud
formation may be linked to cosmic rays -- Nature
August 10, 2011: Antimatter
found orbiting Earth -- a first -- National Geographic
April 10, 2011: Will
space travel break our hearts? -- Astrobiology
July 29, 2010: IceCube
spies unexplained pattern of cosmic rays -- Astronomy
March 12, 2010: Borexino bags
geoneutrinos -- Physics World
November 4, 2009: Mutant
diseases may cripple missions to Mars, beyond -- National
Geographic
September 15, 2009: Space-related
radiation research could help reduce fractures in cancer survivors
-- National Science Biomedical Research Institute
July 8, 2009: Thunderclouds
accelerate cosmic electrons -- Physics World
June 1, 2009: How
do thunderstorms create lightning? High-energy particles from space
used to probe thunderstorms -- Science Daily
May 29, 2009: Theorists
reveal path to true muonium -- SLAC
May 14, 2009: How
to catch a black hole before it eats the world -- New Scientist
May 11, 2009: More
'Star Trek' than 'Snuggie': Student design to protect lunar outpost
from dangerous radiation -- Eurekalert
May 11, 2009: Resolving
the ridge -- HEAPOW
January 26, 2009: CREAM
over ice -- HEAPOW
December 19, 2008: Modeling
radiation exposure for pilots, crew and passengers on commercial
flights -- NASA
October 1, 2008: The first rocket
launch from Cape Canaveral -- APOD
August 25, 2008: Double
first for Large Hadron Collider -- Nature
July 11, 2008: Japanese
particle-physics leader dies -- Physics World
June 5, 2008: Communications glitch
delays Mars lander digging -- Physorg
May 20, 2008: LHCb measures its
first cosmic ray muons -- CERN
May 8, 2008: Joint
ESA/NASA team wins international award -- ESA
April 3, 2008: 'No sun
link' to climate change -- BBC News
February 13, 2007: Predicting
the radiation risk to ESA's astronauts -- ESA
March 21, 2007: Making cosmic gamma rays -- Astronomy.com
January 19, 2007: A new year for BaBar and PEP-II -- Stanford Linear Accelerator Center