1 / 51

Astronomy 305/Frontiers in Astronomy

Astronomy 305/Frontiers in Astronomy. Class web site: http://glast.sonoma.edu/~lynnc/courses/a305 Office: Darwin 329A and NASA E/PO (707) 664-2655 Best way to reach me: lynnc@charmian.sonoma.edu. What is the origin of cosmic rays?. Discovery of Cosmic Rays

zaza
Télécharger la présentation

Astronomy 305/Frontiers in Astronomy

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Astronomy 305/Frontiers in Astronomy Class web site: http://glast.sonoma.edu/~lynnc/courses/a305 Office: Darwin 329A and NASA E/PO (707) 664-2655 Best way to reach me: lynnc@charmian.sonoma.edu Prof. Lynn Cominsky

  2. What is the origin of cosmic rays? • Discovery of Cosmic Rays • General properties of cosmic rays • Cosmic rays from the Sun • Accelerating Cosmic rays • Detecting cosmic rays • The highest energy cosmic rays • New cosmic ray experiments Prof. Lynn Cominsky

  3. Types of Radiation • We have discussed electromagnetic radiation aka light – massless, travel at v=c • When scientists first started studying radiation in the early 1900s, they found 3 different types of rays • Alpha rays – turned out to be Helium nuclei • Beta rays – turned out to be electrons and positrons • Gamma rays – turned out to be light • Detectors invented to study radiation included Geiger counters, film and electroscopes Prof. Lynn Cominsky

  4. Discovery of Cosmic Rays • Viktor Hess (1912) takes electroscope on a balloon flight to 17,500 feet (without oxygen!) • He was trying to find the source of additional radiation seen at ground level that could not be explained by natural sources of radioactive decay Prof. Lynn Cominsky

  5. Hess’ Experiment • Hess used an electroscope – detects charge on 2 thin films • http://www.shep.net/resources/curricular/physics/P30/Unit2/electroscope.html • When the cosmic rays hit the electroscope, they carried away charge • More cosmic rays  electroscope would discharge faster • Hess won the Nobel prize in 1936 for his discovery of cosmic rays Prof. Lynn Cominsky

  6. What are cosmic rays? • Cosmic rays are charged particles such as protons, electrons and nuclei of atoms • They are NOT electromagnetic radiation (aka light) • However, sometimes cosmic rays interact with gas in our galaxy to make gamma rays Prof. Lynn Cominsky

  7. High energy Gamma-ray map Gamma rays in the plane of the galaxy made from cosmic rays hitting gas Prof. Lynn Cominsky

  8. Composition of cosmic rays • Cosmic rays are made of nuclei of different elements (and also electrons) • The percentage of each element of different types is called “composition” • All the nuclei of the elements in the periodic table are present in cosmic rays • The composition of cosmic rays is about the same as that of the elements in the solar system • Various isotopes of elements are also detected though harder to distinguish Prof. Lynn Cominsky

  9. ACE • Advanced Composition Explorer • http://www.srl.caltech.edu/ACE/ • Launched 8/25/97, still operational • Stays near L1 point in Earth-Sun Orbit • Studies particles in solar wind, interplanetary medium, interstellar medium and galactic matter Prof. Lynn Cominsky

  10. Properties of cosmic rays • 90% of cosmic rays are hydrogen nuclei (aka protons) • 9% are helium nuclei • 1% are all the other elements • Thousands of low-energy cosmic rays hit every square meter of the Earth each second • High energy cosmic rays are rare – less than 1 per km2 per century Prof. Lynn Cominsky

  11. Charged particle in magnetic field • http://webphysics.ph.msstate.edu/javamirror/ipmj/java/partmagn/ • Magnetic fields change the direction of travel of charged particles (opposite effect for positive vs. negative particles) • Since the paths of cosmic rays are changed as they travel through space, it is difficult to figure out where they originated Prof. Lynn Cominsky

  12. Cosmic rays vs. gamma rays • Cosmic rays (1) are deflected by magnetic fields in space • Gamma rays (2) travel in straight lines, unaffected by magnetic fields Prof. Lynn Cominsky

  13. Cosmic ray spectrum This is a plot of how many cosmic rays are detected as a function of energy at the top of the Earth’s atmosphere Prof. Lynn Cominsky

  14. Solar flares make low energy CRs • Solar flares originate in sunspots • Magnetic field in sunspots stores energy than is released in solar flares • Sunspots often occur in pairs or groups • The more complex the groups, the greater probability of a resulting flare • A large flare has 106 times more energy than a large earthquake Prof. Lynn Cominsky

  15. Solar prominence seen by Skylab in 1973 Solar Flares SOHO/MDI 11th magnitude earthquake on Sun following solar flare Prof. Lynn Cominsky

  16. 1995 1991 Solar Activity Cycle • Every 11 years, sunspots and X-rays increase • Increased radiation causes Earth’s atmosphere to expand • Solar flares cause radio interference Prof. Lynn Cominsky

  17. Space Weather • For the latest on Space Weather, including solar flares, aurorae, blackouts, and sunspots, see http://www.sec.noaa.gov/SWN/ We are just past Solar Max 23! Prof. Lynn Cominsky

  18. Coronal Mass Ejections • CMEs are the cause of major geomagnetic storms on Earth • CMEs are NOT caused by solar flares, although they may both be signatures of rapid changes in the magnetic field • 1015 - 1016 g of material is ejected into space at speeds from 50 to >1200 km/s • Can only be observed with coronagraphs Prof. Lynn Cominsky

  19. Coronal mass ejection • in UV from SOHO Solar Maximum Mission CME in 1989 Coronal Mass Ejections Prof. Lynn Cominsky

  20. Solar flares affect the Earth • Light in solar flares travels at the speed of light (8.5 minutes to reach Earth) • Relativistic particles travel at near light speed – arrive in 20 minutes to hours • Bulk material ejected from Sun travels at 400-1000 km/hour – takes ~1 day to reach Earth • Charged particles that hit the Earth create aurorae Prof. Lynn Cominsky

  21. Aurorae • Best observed near the magnetic poles • Colors are due to different molecules at different heights in the Earth’s atmosphere – mostly oxygen and nitrogen Recent auroral location Prof. Lynn Cominsky

  22. South Atlantic Anomaly and CRs • Region where the Earth’s magnetic field dips that allows CRs to reach lower into the atmosphere Prof. Lynn Cominsky

  23. Medium-energy Cosmic Rays • 1012 – 1015 eV • Composition at Earth’s atmosphere • 50% protons • ~25% alpha particles • ~13% C/N/O nuclei • <1% electrons • Believed to originate outside of solar system but inside of Milky Way galaxy Prof. Lynn Cominsky

  24. Possible Sources of Galactic CRs • Energetic places in the Galaxy • Black Holes • Neutron stars • Pulsars • Supernovae Red = Xrays Blue = UV Green = ionized H 30 Doradus star forming region Prof. Lynn Cominsky

  25. Accelerating cosmic rays • Medium energy cosmic rays must be accelerated by shock waves in our galaxy • Much research is going on to conclusively prove that supernovae can accelerate cosmic rays to medium energies • Supernovae are believed to be able to accelerate CRs up to the energy of the “knee” 3 x 1015 eV • How do we prove that supernovae are really the acceleration sites for CRs? Prof. Lynn Cominsky

  26. ASCA X-ray Astronomy satellite • ASCA = Advanced Satellite for Cosmology and Astrophysics aka Asuka or flying bird • Japanese X-ray astronomy satellite that observed 1993-2001 Prof. Lynn Cominsky

  27. ASCA and SN1006 Prof. Lynn Cominsky

  28. ASCA and SN1006 • First direct evidence that supernovae can accelerate cosmic rays • Non-thermal synchrotron spectrum at the edges of the supernova where the shocks should occur • Thermal spectrum in the center of the supernova due to hot gas from explosion • Magnetic field in SN1006 exactly the right strength to accelerate CRs up to the “knee” Prof. Lynn Cominsky

  29. Detecting cosmic rays • Cosmic rays are further classified into primaries and secondaries • Primaries are the particles which hit the Earth’s atmosphere • Secondaries are created by interactions between the primaries and the air molecules Prof. Lynn Cominsky

  30. Air showers of secondary CRs • Secondaries are primarily “pions” –elementary particles with charge + - or 0 • Charged pions hit other air molecules • Neutral pions decay into 2 gamma rays which then create positron/electron pairs • Cascade includes UV fluorescent emission, more charged particles and Cerenkov radiation – blue light caused by very fast particles moving through the atmosphere at faster than the local speed of light Prof. Lynn Cominsky

  31. Air showers of secondary CRs Prof. Lynn Cominsky

  32. Shower maximum • Cascade continues until average particle in the shower is not energetic enough to create new particles  “shower maximum” • After shower maximum, particles are absorbed by atmospheric molecules and shower intensity decreases • Shower maximum: for each 1 GeV energy in primary cosmic ray, shower has 1-1.6 particles • For primaries > 1015 eV, enough particles reach ground to be detected in detector array Prof. Lynn Cominsky

  33. Extensive air shower arrays • “Footprint” of shower extends several hundred square meters • Particles are traveling at speeds near c • By comparing arrival times at different detectors, direction of origin can be determined within 1o Prof. Lynn Cominsky

  34. Air Cerenkov telescopes • Cerenkov light is imaged onto segmented optical light telescopes • Showers initiated by gamma rays with E>TeV can be distinguished from CR showers by analyzing the shape of the shower profile Prof. Lynn Cominsky

  35. Ultra-high energy cosmic rays • Believed to originate outside of our Galaxy but perhaps in the local group • For CRs above the “knee” (>3 x 1015 eV) some other acceleration process must occur • Jets from active galaxies are often theorized to be the accelerators • What are they? • Where do they come from? • How did they get so much energy? Prof. Lynn Cominsky

  36. Air “Fluorescent” Detectors • UV light flashes emitted from (mostly) Nitrogen molecules are focused and imaged with detectors on telescopes NOTE: UV light is really scintillation not fluorescence – which is remission at visible light of UV light Prof. Lynn Cominsky

  37. Fly’s Eye Detector Array in Utah Prof. Lynn Cominsky

  38. Fly’s Eye: 1981-1993 • Pixels on sky from telescope array are hexagonal tiles like a fly’s eye – eventually a second array was built for stereo vision movie Prof. Lynn Cominsky

  39. Akeno Giant air shower array • AGASA is in Japan • 111 surface detectors and 27 muon detectors under ground in 100 km2 separated by 1 km • Combining muon and surface detectors yields composition of primary cosmic ray Prof. Lynn Cominsky

  40. Scintillators • Large pieces of material (usually inorganic salts or organic plastics) that emit visible light when hit by CRs • Often used for gamma rays as well AGASA Scintillator Prof. Lynn Cominsky

  41. Muon Detectors • Many of the secondaries are muons – negatively charged particles that are cousins to electrons but 186 times more massive Prof. Lynn Cominsky

  42. Water Cerenkov Detectors • Tanks of water surrounded with photo-multipliers to detect the blue Cerenkov light emitted in the water AGASA Water Cerenkov Detector Prof. Lynn Cominsky

  43. AGASA highest energy event • 3 x 1020 eV – second highest energy cosmic ray ever detected • Shower spread over 6 x 6 km2 • Billions of particles in shower • Primary probably an oxygen nucleus or similar element Prof. Lynn Cominsky

  44. AGASA anisotropy • CRs greater than 1019 eV seen in 11 years of observations with AGASA • Red are > 1020 eV, green are 4-10 x 1019 eV • Circles are clusters of events within 2.5o Prof. Lynn Cominsky

  45. AGASA data – “ankle” to GZK cutoff • >1020 eV energy CRs from > 150 million light years away should not reach the Earth due to collisions with the photons in the microwave background  “GZK cutoff” Prof. Lynn Cominsky

  46. Pierre Auger Observatory (being built) • 2 water Cerenkov arrays to detect the highest energy cosmic rays – one each in the northern and southern hemispheres • Each location occupies 3000 km2 and has 1600 detectors Utah Argentina Prof. Lynn Cominsky

  47. Pierre Auger Observatory (Argentina) • 30 detectors are now operational (out of 1600 planned) • 2 fluorescence detectors are working (out of 24 planned) A building housing a fluorescence detector Prof. Lynn Cominsky

  48. Why should we care about CRs? • We are constantly exposed to background radiation from secondary CRs • Exposure is greater in airplanes, mountains • CRs produce C14 used for carbon dating • CRs produce single-event-upsets (mistakes) in space-based computer chips • We want to understand how nature can accelerate particles to near light speed • Highest energy CRs could signify new physics Prof. Lynn Cominsky

  49. ASPIRE lab on cosmic rays • Go to http://sunshine.chpc.utah.edu/javalabs/java102/hess/index.htm • Try at least the Hess’ balloon ride (Activity 1). Be sure to integrate counts for at least 20 seconds. What do you conclude about the origin of cosmic rays? • Also try activities 2, 3 and 4 if you have time. Prof. Lynn Cominsky

  50. Web Resources • Imagine the Universe http://imagine.gsfc.nasa.gov • Java demo http://webphysics.ph.msstate.edu/javamirror/ipmj/java/partmagn/ • Cosmic and Heliospheric Learning Center http://helios.gsfc.nasa.gov • Astronomy Picture of the Day http://antwrp.gsfc.nasa.gov/apod/ Prof. Lynn Cominsky

More Related