Ever had a frustrating morning and wished you could òÀØHulk-outòÀÙ 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.
It took an accidental dose of cosmic rays to make them fantastic.(Image credit:Marvel/20th Century Fox)
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 sphereòÀÙs 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.
Air showers ensuing from very-high-energy cosmic rays which can enter EarthòÀÙs atmosphere from multiple directions.(Image credit:Simon Swordy/NASA)
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 CoulombòÀÙs 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 balloonòÀÙs 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 EarthòÀÙs 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).
Simulation of a proton (of energy 1e12 eV) hitting and interacting with air molecules in the atmosphere to create a òÀØcosmic ray showeròÀÙ.The portion of the EarthòÀÙs surface beneath the shower is depicted by an 8km by 8km image of ChicagoòÀÙs Lakefront and the proton particle collision is occurring approximately 20km above ground level.(Image credit:Dinoj Surendran via Wikimedia Commons)
Some years later after his own studies into this phenomenon, Robert Andrews Millikan named the ionizing radiation òÀØcosmic raysòÀÙ.Having thus established that cosmic rays travel to Earth through space and came from some source or sources beyond EarthòÀÙs 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 AustrianòÀÙs 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 EarthòÀÙs magnetic fields before atmospheric entry.Likewise they may have òÀØbouncedòÀÙ 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 planetòÀÙs atmosphere from almost all directions possible therefore makes it difficult to discover the high energy particlesòÀÙ 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 EarthòÀÙs magnetic fields it is also now known that more cosmic rays are allowed into the atmosphere towards our planetòÀÙs 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 UniverseòÀÙs 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.
Here pictured with an X-Ray sensitive camera on the NASA satellite ASCA is SN 1006, the supernova remnant in the constellation of Lupus in the Milky Way.Discovered by Frank Gardner and Doug Milne in 1965 it is considered to be the brightest supernova in recorded history.Already known for its òÀØcosmic rayòÀÙ X-ray emissions, in 2010 very high energy gamma ray emissions were also identified by the H.E.S.S. Gamma Ray Observatory.(Image credit:NASA)
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 Marchˆà 2012 a cosmic ray event was recorded in the form of a very powerful solar flare from the Sun.For a 20 hour period FermiòÀÙs LAT (Large Area Telescope) detected gamma-ray emissions coming from this explosion of light that lept into space from the SunòÀÙs 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 SunòÀÙs regular energy output.Astrophysicists have used two instruments, FermiòÀÙs 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.
The latest cosmic ray research:composite sky catalogue using 2 years of Fermi Gamma-ray Space Telescope data.Depicting 1873 objects in total, the brightest patches represent sources with the highest gamma-ray count (at energies greater than 1 billion GeV or electron volts).(Image credit:NASA/DOE/Fermi LAT Collaboration)
However NASAòÀÙs 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 LATòÀÙs òÀØmapòÀÙ 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, theˆà occasional solar activity from our own star.
