Sunday, March 19, 2023

3922 - COSMIC RAYS - where do they come from?

 

-   3922  - COSMIC  RAYS  -  where do they come from?   Cosmic rays produce extensive particle showers that send a cascade of electrons, photons, and muons to Earth's surface.

 


------------  3922  -    COSMIC  RAYS  -  where do they come from?

-   After the discovery of radiation by French physicist Henri Becquerel in 1896, scientists believed atmospheric ionization (where an electron is stripped from an air molecule) occurred only from radioactive elements found in ground rocks or from radioactive gases.

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-    Austrian physicist Victor Hess found an additional source in 1912, when he strapped three electrometers into a balloon and measured atmospheric radiation at an altitude of about 15,000 feet during a total solar eclipse.

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-    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.

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-    In 1937, French physicist Pierre Auger (1899–1993) found that extensive particle showers occur when cosmic rays collide with particles high in the atmosphere, producing a cascade of electrons, positrons, photons, muons (particles similar to electrons but 200 times as massive), and other particles that reach Earth’s surface.

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-    Auger found an ionization rate about four 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.

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-   The Earth is being constantly bombarded from space by cosmic rays of an unknown origin!   Mysterious cosmic rays traveling at speeds approaching that of light constantly pelt Earth’s upper atmosphere from the depths of space, creating high-energy collisions that dwarf those produced in even the most powerful particle colliders. The atmospheric crashes rain down gigantic showers of secondary particles to the surface of our planet.

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-   But despite being discovered more than a century ago, physicists still don’t know where cosmic rays come from.   The short answer to why we can’t trace cosmic rays back to their source: magnetic fields.   Charged cosmic-ray particles are redirected by the magnetic fields they pass through on their long journey through space.   As magnetic fields in space have local, small, randomly oriented structures, a prediction of the exact path of a cosmic-ray particle is impossible.

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-    One thing we do know about cosmic rays is that they are comprised of extremely energetic charged particles,  like protons, alpha particles, and atomic nuclei like helium and iron, with minuscule proportions of antiparticles.

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-     The energies of these particles were monumental in comparison to those of every other particle they had observed until that point.  The average energy of a solar photon is 1.4 electron volts (eV).

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-   An alpha particle emitted during the decay of Uranium-238 possess 4.27*10^6 eV of energy.  Compare that to a cosmic ray proton, which has an energy of some 1 *10^20 eV.

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-   This energy corresponds to that of a tennis ball with a velocity of  124 miles per hour. Only, the tennis ball 10^29 times heavier than the proton. That means a proton can only reach that extreme, macroscopic energy by traveling at almost the speed of light. The universe must be able to accelerate particles to these energies, but we still do not know how it does it.

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-    One of the best ways of accelerating particles is a shock front that occurs when a medium with a large velocity runs into a slower one, producing a shock, a sudden change in the properties of the medium.

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-    What could produce such a shock front? One likely suspect is supernovae. As a shell of shocked material blasted away from an exploding star, it hits the cool interstellar medium that lies between stars, almost like a cosmic tsunami. The phenomena of a traveling shock front can also be found in active galaxies, where huge plasma jet exist.

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-    It was August 1912 when Austrian-American physicist Victor Hess began a series of flights to the upper atmosphere in a hydrogen-filled balloon equipped with an electroscope.  Hess discovered  at a nosebleed-inducing altitude of 3.3 miles, ionization rates of the air were three times that measured at sea level.

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-    He concluded that the source of this ionization was not coming from below our feet, but instead from above. Further measurements made during a solar eclipse also showed the Sun wasn’t the source of this ionization radiation.

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-   During the course of seven balloon trips, Hess discovered cosmic rays , confirmed and named by Robert Millikan in 1925 , coming from beyond our solar system.

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-  To study the collisions caused by cosmic rays, particle physicists retreated below ground, employing increasingly monstrous particle accelerators to slam together particles in an attempt to replicate the collisions that cosmic rays spark in the upper atmosphere.

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-   This quest has culminated with CERN’s Large Hadron Collider (LHC) with a 16-mile circumference deep beneath the French/Swiss border. Yet, despite its impressive size, power and utility, the LHC still can’t reach the energies produced by cosmic ray collisions.

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-    Einstein was working on a wild theory that would radically change our understanding of the fabric of space-time. And this theory, many decades later, could provide the next step to decoding cosmic rays.

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-   The discovery of gravitational waves ,  ripples in space-time predicted by Einstein’s theory of general relativity ,  has made a new form of astronomy possible.

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-      The gravitational-wave signal “GW170817” came from the merger of two neutron stars and was observed in 2017. It was significant for both multi-messenger astronomy and identifying potential sources of cosmic rays.

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-    Not only did this violent merger become the first such event to be detected in both gravitational waves and electromagnetic radiation, but it also confirmed that the merger of compact stellar remnants can accelerate particles to great speeds, creating cosmic rays.

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-    Supernovae, exploding massive stars, are one important source of cosmic rays.  Mysterious cosmic rays traveling at speeds approaching that of light constantly pelt Earth’s upper atmosphere from the depths of space, creating high-energy collisions that dwarf those produced in even the most powerful particle colliders. The atmospheric crashes rain down gigantic showers of secondary particles to the surface of our planet.

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-   What could produce such a shock front? One likely suspect is supernovae. As a shell of shocked material blasted away from an exploding star, it hits the cool interstellar medium that lies between stars, almost like a cosmic tsunami.

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-   The phenomena of a traveling shock front can also be found in active galaxies, where huge plasma jet exist.  This is one of the main reasons why supernova remnants and active galaxies are the most promising candidates for cosmic-ray acceleration.

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-  This energy disparity actually helps dispel fears and ignorance about particle accelerators. If collisions occurring with greater energies in the upper atmosphere don’t create mini-black holes that devour the Earth, why should less energetic collisions deep underground?

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-   The gravitational-wave signal GW170817 came from the merger of two neutron stars and was observed in 2017. It was significant for both multi-messenger astronomy and identifying potential sources of cosmic rays.

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-    Not only did this violent merger become the first such event to be detected in both gravitational waves and electromagnetic radiation, but it also confirmed that the merger of compact stellar remnants can accelerate particles to great speeds, creating cosmic rays.

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                  March 11, 2023    COSMIC  RAYS  -  where do they come from?              3922                                                                                                                          

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--------------------- ---  Sunday, March 19, 2023  ---------------------------

 

 

 

 

         

 

 

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