Cosmic Rays: Messengers From A Million Light-Years Away | Cosmic Vistas | Spark

[Music] [Music] so far out in the milky way a tiny particle of matter flies like a bullet through the vacuum of space propelled by colossal forces the particle moves at nearly the speed of light zipping by stars and the glowing clouds of gas where stars are born suddenly a planet looms directly in front unstoppable the high energy particle rips into the planet's atmosphere it collides with a nitrogen atom destroying both the particle and the atom in a flash of pure energy now that energy creates new particles which cascade downward causing more collisions as they go soon thousands then millions of more particles spread out in a widening cone and then slam into the planet's surface earth has just been hit by a cosmic ray [Music] during the past century astronomers have come up with a multitude of ways to get information from the universe stars give off visible light but they also give off infrared ultraviolet x-rays and other forms of light our eyes can't see what makes cosmic rays so interesting is that they're not another form of light they're bits of matter that are coming directly to us from deep space rays carry information about powerful forces and events taking place thousands or even millions of light years away but to understand what cosmic rays can tell us about the universe we need to know how they are produced in fact it took a while for scientists to understand that cosmic rays even exist the idea has its roots in the discovery of radioactivity by the french physicist ari becquerel in 1896. radioactivity is the particle radiation that comes from atoms breaking apart spontaneously in the environment when it was discovered scientists realized that radioactivity might explain why they could never get an object to hold on to its static electric charge indefinitely because of radioactivity in rocks and soil there are always particles present near earth's surface those particles can interact with anything that has an electric charge causing that charge to gradually leak away over a century ago scientists predicted this effect would disappear if they could take an electrically charged object away from earth's natural radioactivity at the surface the only question was how the answer would come in 1911 when victor hess a physicist from austria began a series of daring balloon flights that would eventually carry him and his instruments to a height of over five kilometers roughly half the cruising altitude of a commercial jet airliner as he ascended hess measured the presence of charged particle radiation like the kind produced by radioactive materials at first the radiation diminished with height exactly as expected but then there was a surprise starting around 1500 meters this situation reversed hess found there was more radiation than at sea level and it was growing with altitude by the time hess landed there was no longer any doubt earth was bathed in radiation coming from above and a new field of science was born scientists eventually started calling the mysterious space radiation cosmic rays by the 1930s the invention of the geiger counter had made it clear that cosmic rays were pummeling earth at an astonishing rate amounting to tens of thousands of incoming particles per square meter every second most of the particles were relatively low in energy but some had enough energy to pass through rock or even up to a meter of lead then in 1938 the french physicist pierre o'jay took some geiger counters high up into the alps to measure cosmic rays there he found that when two geiger counters were set far apart they sometimes recorded cosmic rays arriving at exactly the same time oj had discovered cosmic ray showers bursts of particles that rained down in a widening spray following the destruction of a single much more energetic particle higher up in the atmosphere based on the size of those showers some of the cosmic rays coming in from deep space were clearly more energetic than any particle produced on earth now scientists found themselves embarking on a new quest to understand where in the universe those energetic particles were coming from [Music] thousands of light years from earth a massive star ends its life in a brilliant explosion this is a supernova a stellar cataclysm that is one of the most energetic phenomena in nature as the powerful shock wave expands it creates a wreath of glowing gas like this one called cassiopeia a here revealed in striking detail by the hubble space telescope but could such an event also give rise to cosmic rays the riddle of cosmic rays is one that's being solved in stages the ultimate goal remains understanding how these high energy particles from beyond our solar system are created but to get there scientists first had to figure out what kind of particles they were [Music] for the most part those particles never reach us here on the ground instead they strike the atmosphere and unleash a torrent of secondary particles that shower down like so much subatomic shrapnel by studying these secondary particles in the 1930s and 40s scientists gradually narrowed in on the true nature of cosmic rays what they found is that most cosmic rays about 90 percent of them must be single protons protons are positively charged particles that are part of every atom in the universe but most of them occur in the form of hydrogen atoms atoms that are made of a single proton orbited by a single electron hydrogen is the most abundant element in nature stars are mostly composed of hydrogen and so are the vast clouds of gas out of which new stars form so whatever is making cosmic rays and sending them our way it has plenty of raw material to work with [Music] in 1947 a high altitude balloon experiment revealed that most of the remaining 10 of cosmic rays are made of the nuclei of heavy atoms like iron like protons these atomic nuclei are stripped of their electrons and they've been sent rocketing through space by a powerful force but what even solar flares the giant explosions that erupt from the surface of the sun cannot account for the energies behind these heavier cosmic rays but solar flares do offer us a hint about how cosmic rays are created because solar flares are caused by the release of magnetic energy under the right circumstances a magnetic field can be used to accelerate an electrically charged particle like a proton to enormous speeds today this principle as it work in the large hadron collider the world's largest particle accelerator where huge superconducting magnets are used to send protons careening around a giant ring 27 kilometers in circumference when the protons collide the energy release is enormous generating new particles that allow scientists to explore the fundamental properties of matter amazingly some of the highest energy cosmic rays are millions of times more energetic than the protons in the large hadron collider it means that somewhere out there in space nature has created its own particle accelerators that would dwarf anything humans have built on earth but identifying them has proved a major challenge [Music] starting in the 1980s an experiment called fly's eye in the remote utah desert used sensitive detectors to spot the faint ultraviolet glow of cosmic ray air showers high up in the atmosphere [Music] this allowed researchers to see what direction any particular cosmic ray was coming from in the sky yet this did not help scientists figure out where cosmic rays ultimately come from the reason is that the space between the stars is a complex network of magnetic fields that thread their way around our galaxy and these fields have been bent and twisted by the turbulent motions of ionized interstellar gas the magnetic fields completely scramble the directions of cosmic rays moving through the galaxy so that from earth's point of view they appear to be coming from all over the sky leaving no hint about where they originally came from in their efforts to explain cosmic rays scientists had run into a significant roadblock one that would require them to search the heavens in a new and different way [Music] this is our milky way galaxy home to hundreds of billions of stars and vast clouds of dust and gas that stretch on for thousands of light years it is a huge and complex system and hidden somewhere within its depths are the sources of high-energy particles we call cosmic rays as early as 1949 the nuclear physicist enrico fermi proposed the idea that cosmic rays are produced when protons and other charged particles are accelerated to high speeds by bouncing around within a changing magnetic field but where in the galaxy might conditions make such bouncing around possible because cosmic ray particles are intensely energetic the sources that create them must be able to somehow provide that energy and those sources may also give themselves away by throwing off a high-energy form of light called x-rays here on earth x-rays from space are absorbed by our atmosphere so x-ray telescopes must do their work orbiting high above earth's surface today the chandra x-ray observatory is our most discerning x-ray eye on the sky chandra has been used to peer into some of the hottest and most energetic regions of the galaxy revealing views like this of the karina nebula where interstellar gas is cooked to millions of degrees by newborn giant stars this is a high energy environment but not one that has the kind of magnetic fields needed to accelerate cosmic ray particles [Music] so instead of looking at places where stars are born cosmic ray hunters have zeroed in on those places where giant stars have died violently this spectacular ring is the remnant of a supernova a vast stellar explosion that sprays matter outward in all directions creating a rapidly expanding shock wave the leading edge of this bubble can move at tens of thousands of kilometers per second but that's still nowhere near the speed of a cosmic ray particle however scientists after fermi realized that supernova shockwaves can compress and strengthen magnetic fields in the surrounding gas then charged particles moving back and forth across the shock wave can pick up more and more energy through a process called fermi acceleration eventually the particles would be moving fast enough to break away from the shock wave and fly off into the galaxy here at last was a theory that could explain cosmic rays but proving it would require another kind of space observatory fittingly that observatory is nasa's fermi space telescope named after enrico fermi it has special detectors that can pick up gamma rays a form of light even more energetic than x-rays five four three launched in 2008 the fermi telescope had been used to study the most extreme phenomena in the universe a gamma-ray telescope searching for unseen physics like the super-massive black holes that lie at the centers of distant galaxies or mysterious explosions known as gamma-ray bursts and fermi has also turned its attention to two of the most interesting supernova remnants in the milky way one is w44 a dramatic shell of expanding gas located 10 000 light years away in the constellation aquila the eagle the other is ic 443 nicknamed the jellyfish nebula it lies roughly 5 000 light years away in the constellation gemini what these two colorful bubbles have in common is that they are both the result of supernova explosions expanding into dense clouds of interstellar gas in theory this should be the perfect situation for generating cosmic rays by fermi acceleration the fermi spacecraft is the perfect tool for testing this idea its sensitive detectors can distinguish between gamma rays that are produced by different kinds of physical processes but it would take more than four years of gathering data with fermi for scientists to be sure finally in february 2013 they were ready to reveal their results what they had found was a clear signal the first ever seen of protons at high energies occasionally colliding to produce gamma rays the type of signal exactly matched what was expected if the protons were being accelerated on their way to becoming cosmic rays 100 years after cosmic rays were first discovered the fermi telescope had finally captured a glimpse of cosmic ray creation scientists now know more about cosmic rays than ever before but the search doesn't end here although they are rare the highest energy cosmic rays are so powerful even a supernova shockwave isn't enough to drive them so now the search for new sources of cosmic rays is reaching beyond the boundaries of the milky way this is m87 a giant galaxy about 60 million light years from our own deep in its core lies a black hole so huge its mass is equivalent to more than 6 billion suns as it devours gas from the surrounding environment the rapid spin of the black hole causes some of the gas to escape forming a jet that extends hundreds of thousands of light years into intergalactic space the jet is wrapped in magnetic fields that may just be strong enough to create what are known as ultra high energy cosmic rays because they are so rare the experiments that hunt for these particles are huge covering thousands of square kilometers in an effort to capture just a handful of the most energetic particles in nature [Music] but if the theory proves correct for the first time these experiments may be able to prove that we are being hit by matter from another galaxy thanks to the discovery of cosmic rays we know we have a direct connection to some of the most powerful phenomena in the universe now as a new chapter of exploration opens before us we are learning just how astonishing that link to the cosmos may prove to be

Channel: Spark

Views: 97,359

Keywords: NASA, Saturn, Spark, astrophysics, atmospheres, celestial events, cosmic evolution, cosmic origins, cosmology, dark energy, dark matter, galaxy evolution, gamma rays, gravitational waves, learn, millions of light-years, particles, science, solar bodies, solar system, stars

Id: -J54HjCRdaA

Length: 22min 11sec (1331 seconds)

Published: Wed Jul 28 2021