- 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.
-
- 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.
-
- 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
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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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).
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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. This is one
of the main reasons why supernova remnants and active galaxies are the most
promising candidates for cosmic-ray acceleration.
-
- 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?
-
- 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.
-
- 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.
-
March 11, 2023 COSMIC
RAYS - where do they come from? 3922
----------------------------------------------------------------------------------------
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------ “Jim Detrick” -----------
--------------------- --- Sunday, March 19, 2023
---------------------------
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