Ever had a frustrating morning and wished you could ‘Hulk-out’ or that some superhuman abilities were within your grasp even for the briefest of moments?With the psyche of superheroes very much to the fore in contemporary culture, it is perhaps interesting to learn that emissions similar to those of human ability-altering comic book lore are invisibly blasting all of us and the ground we stand on hundreds of times every second.
Exactly 100 years ago an Austrian named Victor Hess discovered cosmic rays.What he found in part solved a scientific mystery that had baffled minds since the 18th Century. Although air was and is still known to be an insulator of heat, back in the 1780s it was also believed to be an insulator of electrical charge. French physicist Charles-Augustin de Coulomb was therefore stunned when the results of his experiment into this phenomenon were in sharp contrast to expectations. Namely a hollow electrically-charged sphere (filled with air) seemed to spontaneously lose its charge even though it was encased in a lead-lined chamber. Since the properties of lead as an effective shield to radioactive penetration were well-known by the early 1900s, the sphere’s loss of charge from within the specially-prepared case was an even greater mystery. Only two things were clear. The notion of air as an electrical insulator per sae needed to be thoroughly revised, and if air did on occasions display the ability to conduct electricity, some as yet undiscovered additional factor was triggering this occurrence.
Subsequent investigations added the next crucial pieces to the jigsaw puzzle.Scientists stumbled on the truth that air molecules would conduct electricity once ionized by X-rays or charged particles.The question of course still remained, where had the sufficiently energised particles come from, that had so powerfully penetrated the lead-lined chamber and so affected De Coulomb’s charged sphere?The answer came at last, over a century later.During a hot air balloon flight in August 1912 that brought him to Bad Saarow in Brandenburg, Germany, Viktor Hess took a number of readings with an ionisation chamber that showed ionising radiation significantly increased the higher he flew.Although on the ground our planet was known to display some naturally-occurring radioactivity, at the balloon’s maximum altitude of 5350m Hess recorded ionizing radiation magnitudes three times that found at sea level.The conclusion from these measurements was self-evident.The farther one moved away from the Earth’s surface, or rather, the closer one moved toward space, the greater the count of high energy charged particles.
(In the same way the extended time spent at high altitude explains how long-haul airline pilots double their annual ionizing radiation quota).
Some years later after his own studies into this phenomenon, Robert Andrews Millikan named the ionizing radiation ‘cosmic rays’.Having thus established that cosmic rays travel to Earth through space and came from some source or sources beyond Earth’s atmosphere, the scientific race to identify their origins began.One scientific school of thought was that these high-energy particles were showered on the Earth solely from the Sun.Again we have Hess to thank for disposing of this misconception.Taking his hot air balloon to the skies once again the Austrian’s measurements revealed no drop in ionization during a solar eclipse.Although significant facts have been gleaned from the last 100 years of continuous investigative study, the precise source or sources of cosmic rays remains somewhat of a mystery.
One enormous challenge facing scientists seeking to find answers is that the cosmic ray particles they are studying have been influenced by Earth’s magnetic fields before atmospheric entry.Likewise they may have ‘bounced’ off a range of interstellar matter along the way, and so may have changed direction since they left their distant source in space.Entering our planet’s atmosphere from almost all directions possible therefore makes it difficult to discover the high energy particles’ origin(s) in outer space.In terms of what we do know about cosmic rays, scientists agree that these high energy subatomic particles are mostly protons of the elements that naturally occur in the Universe and travel through space at very high speeds.Low-medium energy cosmic rays are thought to be composed of heavier nuclei.With an understanding of the paths and shape of Earth’s magnetic fields it is also now known that more cosmic rays are allowed into the atmosphere towards our planet’s poles.Research has revealed two main types of cosmic ray.Primary rays and secondary rays.Scientists believe that lower energy secondary particles are generated in a process called cosmic ray spallation.For example, when primary ray nuclei of the elements carbon and oxygen collide with interstellar matter-(the gas, dust, and rock existent throughout space), a shower of elements with heavier nuclei such as lithium, beryllium, and boron are created.Likewise when primary rays in the form of iron and nickel nuclei collide with the space material found between stars, secondary rays such as scandium, titanium, vanadium, and manganese ions are formed.Despite knowing that these electrically charged particles can have energies up to 100 million times more than what can be created in man-made accelerators, astrophysicists are not sure which of the Universe’s many natural particle accelerators are propelling them at such incredible speeds.Binary star systems and supernovae explosions are just two of the possible cosmic particle accelerators.
The IceCube Neutrino Observatory in Antarctica has a huge telescope and since its completion in December 2010 has greatly increased prospects of solving the cosmic ray source question once and for all.Although normally difficult to find, this specialised detector with 5160 optical sensors observes high energy particles called neutrinos, (believed to accompany cosmic ray radiation) by identifying their ghostly-bluish interactions in one cubic kilometre of glacial ice.Appearing in nuclear reactions and particle collisions neutrinos can pass right through people and the planet completely void of interaction with other particles.Although GRB or Gamma Ray Burst fireballs are the most powerful explosions in the cosmos and can temporarily outshine everything else when seen from halfway across the visible Universe, between May 2008 and April 2010 the SWIFT and Fermi satellites recorded a complete absence of neutrinos from 300 GRBs.Somewhat surprisingly, this finding eliminated GRBs from the list of possible sources of cosmic rays.
Much closer to home, on 7 March 2012 a cosmic ray event was recorded in the form of a very powerful solar flare from the Sun.For a 20 hour period Fermi’s LAT (Large Area Telescope) detected gamma-ray emissions coming from this explosion of light that lept into space from the Sun’s surface.With 2 billion times the energy levels of visible light or approximately 4 billion electron volts (GeV) this single event was effectively 1000 times greater than the Sun’s regular energy output.Astrophysicists have used two instruments, Fermi’s LAT and the GBM (Gamma-ray burst monitor) to calculate a potential acceleration of particles from some solar flares to two thirds the speed of light within 3 seconds.However thinking on the whole, is that for most of the time, the Sun is responsible for only some of the lowest energy cosmic rays, light nuclei and protons, but for the bulk of the cosmic rays that bombard our planet, they come from outside our Solar System.
However NASA’s Fermi Gamma-ray space telescope has observed much more.Where secondary cosmic rays are often the most-easily observed in this field of research, in terms of primary cosmic ray detection perhaps one of the greatest revelations to date has been the LAT’s ‘map’ of the Universe in gamma rays.These detectable photons, emitted when the highest energy protons are accelerated to close to the speed of light (and become cosmic rays), have helped point to some potential accelerators within our solar system and without, bright pulsars, active galaxies billions of light years away, and as we are already aware, the occasional solar activity from our own star.
Compared to the directional confusion the magnetic fields around Earth and within the Milky Way play with the majority of the fast-moving incoming subatomic particles, the direction from which the highest energy cosmic rays arrive can be used to trace their point of origin in space within approximately 3 degrees.These more powerful particles are thought to remain uninfluenced by the magnetic fields and so can more accurately indicate which suitably large astronomical object in the Universe they have come from.On the other hand, cosmic rays composed of up to 100 000 000 000 000 000eV are believed to originate within our galaxy.
Earth’s atmosphere and magnetic field to a greater or lesser degree shield the Earth and its inhabitants from cosmic rays.For although ten thousand particles of energy 1GeV pass through us and each square metre of ground every second, only 1 cosmic ray of energy 1000 GeV does so in the same length of time.So need we be concerned with the super-high-energy cosmic particles constantly bombarding the Earth from space or the cell-mutating and DNA-destroying properties of the gamma-rays associated with them?With only a single particle of more than 10 000 000 000 000 000 000 eV reaching a single square kilometre of ground each year, the answer is unequivocally no.
So with the long-awaited questions as to the sources of cosmic radiation at least in part answered, what is the next major challenge the astrophysicists are preparing to tackle?The answer is in proving the existence of perhaps the most mysterious substances in space.Attempting effectively to look back in time and unlock secrets as to the beginnings of the Universe, the Alpha Magnetic Spectrometer is the latest addition to the high-tech instrumentation of the International Space Station.
Also known as AMS-02 this device weighing 6.7 tons (6717kg) has, since its installation in May 2010 been attempting to find evidence of unusual types of matter such as investigative antimatter and dark matter.This it attempts to do by measuring cosmic rays.Worth four times as much as any of Earth’s largest particle detectors the Alpha Magnetic Spectrometer is the most complex ever to be sent into space.Although no dark matter particles have as yet been detected, this sensitive instrument has reported 18 billion cosmic ray events.However with a reply found at last for some of the biggest cosmic ray questions, surely it will just be a matter of time.
(Article by Nick Parke, Education Support Officer)
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