-
3828 - 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.
--------- 3828 - 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. Much later, in 1936, Hess received the Nobel Prize in physics for the
discovery of what we now call cosmic rays.
-
- 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.
-
- One thing we certainly 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
miniscule proportions of antiparticles.
-
- The average energy of a solar photon is
approximately 1.4 electron volts (eV). For reference, a flying mosquito has an
energy of about 1 trillion eV, or 1x10^12 eV, but a mosquito is also much, much
larger than a single particle. Meanwhile, 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 1x10^20 eV.
-
- This energy corresponds to that of a tennis
ball smashed with a velocity of around 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 travelling 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. In the case of the universe, the changed
properties are velocity and density, and even magnetic fields. Luckily for the
cosmic rays, the field becomes highly turbulent in that process. And the
combination of a shock front with turbulence is a great particle accelerator.
-
- But 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 travelling shock front
can also be found in active galaxies, where huge plasma jet exist.
-
- It is ironic that science’s journey to
discover the source of high-energy particles from space began in the upper
atmosphere, and has since moved deep underground.
-
- 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. His aim: to take
measurements of ionizing radiation. At the time, it was widely believed that
radiation from the Earth itself was responsible for this phenomenon of knocking
electrons off atoms. Should this be the case, however ionization should be
strongest near the planet’s surface.
-
- That’s not what Hess found. Hess discovered something startling. 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 these 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.
-
- 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, allowing us to investigate events
and objects that we could never hope to observe in the electromagnetic spectrum
alone.
-
- This combination of electromagnetic or
“traditional” astronomy and gravitational-wave detections (along with detecting
neutrinos, which are ghost-like particles with virtually no mass or electric
charge) is known as “multi-messenger astronomy”.
-
- 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.
-
- As multi-messenger astronomy is refined,
observations such as this, as well as the information they unlock, should
become more commonplace. There is no
other way than multi-messenger astronomy to understand the origin and impact of
cosmic rays.
-
January 15, 2022 COSMIC
RAYS - where do they come from? 3828
----------------------------------------------------------------------------------------
-----
Comments appreciated and Pass it on to whomever is interested. ---
--- Some
reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email
feedback, corrections, request for copies or Index of all reviews
---
to: ------ jamesdetrick@comcast.net ------
“Jim Detrick” -----------
--------------------- --- Sunday, January 15, 2023 ---------------------------
-
No comments:
Post a Comment