Astronomy

The Origins of Cosmic Rays



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Cosmic rays are any particles originating beyond the Earth's atmosphere. They move at incredibly fast speeds and travel billions of miles. Different types of cosmic rays have different origins. There are galactic cosmic rays, solar energetic cosmic rays and anomalous cosmic rays. Each is named referring to their source.

First, galactic cosmic rays (GCRs) originate outside of the solar system but still within the Milky Way Galaxy. Due to high speeds, nearly reaching the speed of light, the electrons of the particles have been stripped away, leaving only nuclei. The vast majority of galactic cosmic rays are believed to have been traveling the galaxy for millions of years and are the result of supernova shockwaves. They have probably circled the galaxy several times and some became trapped due to the Milky Way's magnetic field. As they pass through interstellar space, they interact with one another and emit gamma rays.  

Next, solar energetic cosmic rays, or solar energetic particles (SEPs), are closely associated with solar flares from the Sun. Plasma heating, acceleration and some other forces propel these particles away from the Sun. Solar flares project nuclei into space. The composition of solar flares varies from flare to flare, so the composition of this type of cosmic ray also varies. These types of cosmic rays have lower energies than the other types.

Lastly, anomalous cosmic rays (ACRs) originate in interstellar space at the edge of the heliopause. The heliopause is the boundary between our solar system's heliosphere and the rest of the universe beyond. It is where the solar magnetic field and the solar winds stop. Anomalous cosmic rays are the result of ions experiencing termination shock with the heliopause. The ions repeatedly collide with the magnetic field, gaining energy in the process. Sometimes they gain enough energy and accelerate, allowing them to enter the heliosphere. The mechanism behind the acceleration is still a mystery. Anomalous cosmic rays are not believed to have experienced processes as violent as those involved in the creation of galactic cosmic rays. They move at lower speeds and have lower energies than GCRs.

The various types of cosmic rays are studied in order to shed light on acceleration processes in the galaxy. They can also reveal information about the composition of the Sun and other interstellar bodies. Galactic cosmic rays are from the Milky Way Galaxy beyond this solar system, while solar energetic particles are from the Sun. Anomalous cosmic rays are the most mysterious and are from interstellar space.

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  • InfoBoxCallToAction ActionArrowhttp://helios.gsfc.nasa.gov/cosmic.html
  • InfoBoxCallToAction ActionArrowhttp://helios.gsfc.nasa.gov/gcr.html
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