9/16/03Prof. Lynn Cominsky1 Class web site: Office: Darwin 329A and NASA E/PO (707) Best way to reach me: Astronomy 305/Frontiers in Astronomy

9/16/03Prof. Lynn Cominsky2 What is the origin of cosmic rays? Discovery of Cosmic Rays Discovery of Cosmic Rays General properties of cosmic rays General properties of cosmic rays Cosmic rays from the Sun Cosmic rays from the Sun Accelerating Cosmic rays Accelerating Cosmic rays Detecting cosmic rays Detecting cosmic rays The highest energy cosmic rays The highest energy cosmic rays New cosmic ray experiments New cosmic ray experiments

9/16/03Prof. Lynn Cominsky3 Types of Radiation We have discussed electromagnetic radiation aka light – massless, travel at v=c 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 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 Alpha rays – turned out to be Helium nuclei Beta rays – turned out to be electrons and positrons Beta rays – turned out to be electrons and positrons Gamma rays – turned out to be light Gamma rays – turned out to be light Detectors invented to study radiation included Geiger counters, film and electroscopes Detectors invented to study radiation included Geiger counters, film and electroscopes

9/16/03Prof. Lynn Cominsky4 Discovery of Cosmic Rays 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 Viktor Hess (1912) takes electroscope on a balloon flight to 17,500 feet (without oxygen!) Viktor Hess (1912) takes electroscope on a balloon flight to 17,500 feet (without oxygen!)

9/16/03Prof. Lynn Cominsky5 Hess’ Experiment Hess used an electroscope – detects charge on 2 thin films Hess used an electroscope – detects charge on 2 thin films 0/Unit2/electroscope.html 0/Unit2/electroscope.html 0/Unit2/electroscope.html 0/Unit2/electroscope.html When the cosmic rays hit the electroscope, they carried away charge When the cosmic rays hit the electroscope, they carried away charge More cosmic rays  electroscope would discharge faster More cosmic rays  electroscope would discharge faster Hess won the Nobel prize in 1936 for his discovery of cosmic rays Hess won the Nobel prize in 1936 for his discovery of cosmic rays

9/16/03Prof. Lynn Cominsky6 What are cosmic rays? Cosmic rays are charged particles such as protons, electrons and nuclei of atoms Cosmic rays are charged particles such as protons, electrons and nuclei of atoms They are NOT electromagnetic radiation (aka light) They are NOT electromagnetic radiation (aka light) However, sometimes cosmic rays interact with gas in our galaxy to make gamma rays However, sometimes cosmic rays interact with gas in our galaxy to make gamma rays

9/16/03Prof. Lynn Cominsky7 High energy Gamma-ray map Gamma rays in the plane of the galaxy made from cosmic rays hitting gas

9/16/03Prof. Lynn Cominsky8 Composition of cosmic rays Cosmic rays are made of nuclei of different elements (and also electrons) Cosmic rays are made of nuclei of different elements (and also electrons) The percentage of each element of different types is called “composition” 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 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 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 Various isotopes of elements are also detected though harder to distinguish

9/16/03Prof. Lynn Cominsky9 ACE Advanced Composition Explorer Advanced Composition Explorer Launched 8/25/97, still operational Launched 8/25/97, still operational Stays near L1 point in Earth-Sun Orbit Stays near L1 point in Earth-Sun Orbit Studies particles in solar wind, interplanetary medium, interstellar medium and galactic matter Studies particles in solar wind, interplanetary medium, interstellar medium and galactic matter

9/16/03Prof. Lynn Cominsky10 Properties of cosmic rays 90% of cosmic rays are hydrogen nuclei (aka protons) 90% of cosmic rays are hydrogen nuclei (aka protons) 9% are helium nuclei 9% are helium nuclei 1% are all the other elements 1% are all the other elements Thousands of low-energy cosmic rays hit every square meter of the Earth each second 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 km 2 per century High energy cosmic rays are rare – less than 1 per km 2 per century

9/16/03Prof. Lynn Cominsky11 Charged particle in magnetic field mirror/ipmj/java/partmagn/ mirror/ipmj/java/partmagn/ mirror/ipmj/java/partmagn/ mirror/ipmj/java/partmagn/ Magnetic fields change the direction of travel of charged particles (opposite effect for positive vs. negative particles) 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 Since the paths of cosmic rays are changed as they travel through space, it is difficult to figure out where they originated

9/16/03Prof. Lynn Cominsky12 Cosmic rays vs. gamma rays Cosmic rays (1) are deflected by magnetic fields in space Cosmic rays (1) are deflected by magnetic fields in space Gamma rays (2) travel in straight lines, unaffected by magnetic fields Gamma rays (2) travel in straight lines, unaffected by magnetic fields

9/16/03Prof. Lynn Cominsky13 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

9/16/03Prof. Lynn Cominsky14 Solar flares make low energy CRs Solar flares originate in sunspots Solar flares originate in sunspots Magnetic field in sunspots stores energy than is released in solar flares Magnetic field in sunspots stores energy than is released in solar flares Sunspots often occur in pairs or groups Sunspots often occur in pairs or groups The more complex the groups, the greater probability of a resulting flare The more complex the groups, the greater probability of a resulting flare A large flare has 10 6 times more energy than a large earthquake A large flare has 10 6 times more energy than a large earthquake

9/16/03Prof. Lynn Cominsky15 Solar Flares Solar prominence seen by Skylab in 1973 SOHO/MDI 11th magnitude earthquake on Sun following solar flare

9/16/03Prof. Lynn Cominsky16 Solar Activity Cycle Every 11 years, sunspots and X- rays increase Every 11 years, sunspots and X- rays increase Increased radiation causes Earth ’ s atmosphere to expand Increased radiation causes Earth ’ s atmosphere to expand Solar flares cause radio interference Solar flares cause radio interference

9/16/03Prof. Lynn Cominsky17 Space Weather For the latest on Space Weather, including solar flares, aurorae, blackouts, and sunspots, see For the latest on Space Weather, including solar flares, aurorae, blackouts, and sunspots, see We are just past Solar Max 23!

9/16/03Prof. Lynn Cominsky18 Coronal Mass Ejections CMEs are the cause of major geomagnetic storms on Earth 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 CMEs are NOT caused by solar flares, although they may both be signatures of rapid changes in the magnetic field g of material is ejected into space at speeds from 50 to >1200 km/s g of material is ejected into space at speeds from 50 to >1200 km/s Can only be observed with coronagraphs Can only be observed with coronagraphs

9/16/03Prof. Lynn Cominsky19 Coronal Mass Ejections Coronal mass ejection in UV from SOHO Solar Maximum Mission CME in 1989

9/16/03Prof. Lynn Cominsky20 Solar flares affect the Earth Light in solar flares travels at the speed of light (8.5 minutes to reach 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 Relativistic particles travel at near light speed – arrive in 20 minutes to hours Bulk material ejected from Sun travels at km/hour – takes ~1 day to reach Earth Bulk material ejected from Sun travels at km/hour – takes ~1 day to reach Earth Charged particles that hit the Earth create aurorae Charged particles that hit the Earth create aurorae

9/16/03Prof. Lynn Cominsky21 Aurorae Best observed near the magnetic poles Best observed near the magnetic poles Colors are due to different molecules at different heights in the Earth’s atmosphere – mostly oxygen and nitrogen Colors are due to different molecules at different heights in the Earth’s atmosphere – mostly oxygen and nitrogen Recent auroral location

9/16/03Prof. Lynn Cominsky22 South Atlantic Anomaly and CRs Region where the Earth’s magnetic field dips that allows CRs to reach lower into the atmosphere Region where the Earth’s magnetic field dips that allows CRs to reach lower into the atmosphere

9/16/03Prof. Lynn Cominsky23 Medium-energy Cosmic Rays 10 – 10 eV – eV Composition at Earth’s atmosphere Composition at Earth’s atmosphere 50% protons 50% protons ~25% alpha particles ~25% alpha particles ~13% C/N/O nuclei ~13% C/N/O nuclei <1% electrons <1% electrons Believed to originate outside of solar system but inside of Milky Way galaxy Believed to originate outside of solar system but inside of Milky Way galaxy

9/16/03Prof. Lynn Cominsky24 Possible Sources of Galactic CRs Energetic places in the Galaxy Energetic places in the Galaxy Black Holes Black Holes Neutron stars Neutron stars Pulsars Pulsars Supernovae Supernovae 30 Doradus star forming region Red = Xrays Blue = UV Green = ionized H

9/16/03Prof. Lynn Cominsky25 Accelerating cosmic rays Medium energy cosmic rays must be accelerated by shock waves in our galaxy 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 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 eV Supernovae are believed to be able to accelerate CRs up to the energy of the “knee” 3 x eV How do we prove that supernovae are really the acceleration sites for CRs? How do we prove that supernovae are really the acceleration sites for CRs?

9/16/03Prof. Lynn Cominsky26 ASCA X-ray Astronomy satellite ASCA = Advanced Satellite for Cosmology and Astrophysics aka Asuka or flying bird ASCA = Advanced Satellite for Cosmology and Astrophysics aka Asuka or flying bird Japanese X-ray astronomy satellite that observed Japanese X-ray astronomy satellite that observed

9/16/03Prof. Lynn Cominsky27 ASCA and SN1006

9/16/03Prof. Lynn Cominsky28 ASCA and SN1006 First direct evidence that supernovae can accelerate cosmic rays First direct evidence that supernovae can accelerate cosmic rays Non-thermal synchrotron spectrum at the edges of the supernova where the shocks should occur 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 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” Magnetic field in SN1006 exactly the right strength to accelerate CRs up to the “knee”

9/16/03Prof. Lynn Cominsky29 Detecting cosmic rays Cosmic rays are further classified into primaries and secondaries Cosmic rays are further classified into primaries and secondaries Primaries are the particles which hit the Earth’s atmosphere Primaries are the particles which hit the Earth’s atmosphere Secondaries are created by interactions between the primaries and the air molecules Secondaries are created by interactions between the primaries and the air molecules

9/16/03Prof. Lynn Cominsky30 Air showers of secondary CRs Secondaries are primarily “pions” – elementary particles with charge + - or 0 Secondaries are primarily “pions” – elementary particles with charge + - or 0 Charged pions hit other air molecules Charged pions hit other air molecules Neutral pions decay into 2 gamma rays which then create positron/electron pairs 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 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

9/16/03Prof. Lynn Cominsky31 Air showers of secondary CRs

9/16/03Prof. Lynn Cominsky32 Shower maximum Cascade continues until average particle in the shower is not energetic enough to create new particles  “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 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 particles Shower maximum: for each 1 GeV energy in primary cosmic ray, shower has particles For primaries > eV, enough particles reach ground to be detected in detector array For primaries > eV, enough particles reach ground to be detected in detector array

9/16/03Prof. Lynn Cominsky33 Extensive air shower arrays “Footprint” of shower extends several hundred square meters “Footprint” of shower extends several hundred square meters Particles are traveling at speeds near c Particles are traveling at speeds near c By comparing arrival times at different detectors, direction of origin can be determined within 1 o By comparing arrival times at different detectors, direction of origin can be determined within 1 o

9/16/03Prof. Lynn Cominsky34 Air Cerenkov telescopes Cerenkov light is imaged onto segmented optical light 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 Showers initiated by gamma rays with E>TeV can be distinguished from CR showers by analyzing the shape of the shower profile

9/16/03Prof. Lynn Cominsky35 Ultra-high energy cosmic rays Believed to originate outside of our Galaxy but perhaps in the local group Believed to originate outside of our Galaxy but perhaps in the local group For CRs above the “knee” (>3 x eV) some other acceleration process must occur For CRs above the “knee” (>3 x eV) some other acceleration process must occur Jets from active galaxies are often theorized to be the accelerators Jets from active galaxies are often theorized to be the accelerators What are they? What are they? Where do they come from? Where do they come from? How did they get so much energy? How did they get so much energy?

9/16/03Prof. Lynn Cominsky36 Air “Fluorescent” Detectors UV light flashes emitted from (mostly) Nitrogen molecules are focused and imaged with detectors on telescopes 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

9/16/03Prof. Lynn Cominsky37 Fly’s Eye Detector Array in Utah

9/16/03Prof. Lynn Cominsky38 Fly’s Eye: Pixels on sky from telescope array are hexagonal tiles like a fly’s eye – eventually a second array was built for stereo vision Pixels on sky from telescope array are hexagonal tiles like a fly’s eye – eventually a second array was built for stereo vision movie

9/16/03Prof. Lynn Cominsky39 Akeno Giant air shower array AGASA is in Japan AGASA is in Japan 111 surface detectors and 27 muon detectors under ground in 100 km 2 separated by 1 km 111 surface detectors and 27 muon detectors under ground in 100 km 2 separated by 1 km Combining muon and surface detectors yields composition of primary cosmic ray Combining muon and surface detectors yields composition of primary cosmic ray

9/16/03Prof. Lynn Cominsky40 Scintillators Large pieces of material (usually inorganic salts or organic plastics) that emit visible light when hit by CRs 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 Often used for gamma rays as well AGASA Scintillator

9/16/03Prof. Lynn Cominsky41 Muon Detectors Many of the secondaries are muons – negatively charged particles that are cousins to electrons but 186 times more massive Many of the secondaries are muons – negatively charged particles that are cousins to electrons but 186 times more massive

9/16/03Prof. Lynn Cominsky42 Water Cerenkov Detectors Tanks of water surrounded with photo- multipliers to detect the blue Cerenkov light emitted in the water Tanks of water surrounded with photo- multipliers to detect the blue Cerenkov light emitted in the water AGASA Water Cerenkov Detector

9/16/03Prof. Lynn Cominsky43 AGASA highest energy event 3 x eV – second highest energy cosmic ray ever detected 3 x eV – second highest energy cosmic ray ever detected Shower spread over 6 x 6 km 2 Shower spread over 6 x 6 km 2 Billions of particles in shower Billions of particles in shower Primary probably an oxygen nucleus or similar element Primary probably an oxygen nucleus or similar element

9/16/03Prof. Lynn Cominsky44 AGASA anisotropy CRs greater than eV seen in 11 years of observations with AGASA CRs greater than eV seen in 11 years of observations with AGASA Red are > eV, green are 4-10 x eV Red are > eV, green are 4-10 x eV Circles are clusters of events within 2.5 o Circles are clusters of events within 2.5 o

9/16/03Prof. Lynn Cominsky45 AGASA data – “ankle” to GZK cutoff >10 20 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” >10 20 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”

9/16/03Prof. Lynn Cominsky46 Pierre Auger Observatory (being built) 2 water Cerenkov arrays to detect the highest energy cosmic rays – one each in the northern and southern hemispheres 2 water Cerenkov arrays to detect the highest energy cosmic rays – one each in the northern and southern hemispheres Each location occupies 3000 km 2 and has 1600 detectors Each location occupies 3000 km 2 and has 1600 detectors Utah Argentina

9/16/03Prof. Lynn Cominsky47 Pierre Auger Observatory (Argentina) 30 detectors are now operational (out of 1600 planned) 30 detectors are now operational (out of 1600 planned) 2 fluorescence detectors are working (out of 24 planned) 2 fluorescence detectors are working (out of 24 planned) A building housing a fluorescence detector

9/16/03Prof. Lynn Cominsky48 Why should we care about CRs? We are constantly exposed to background radiation from secondary CRs We are constantly exposed to background radiation from secondary CRs Exposure is greater in airplanes, mountains Exposure is greater in airplanes, mountains CRs produce C 14 used for carbon dating CRs produce C 14 used for carbon dating CRs produce single-event-upsets (mistakes) in space-based computer chips CRs produce single-event-upsets (mistakes) in space-based computer chips We want to understand how nature can accelerate particles to near light speed We want to understand how nature can accelerate particles to near light speed Highest energy CRs could signify new physics Highest energy CRs could signify new physics

9/16/03Prof. Lynn Cominsky49 ASPIRE lab on cosmic rays Go to java102/hess/index.htm Go to java102/hess/index.htm java102/hess/index.htm 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? 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. Also try activities 2, 3 and 4 if you have time.

9/16/03Prof. Lynn Cominsky50 Web Resources Imagine the Universe Imagine the Universe Java demo mirror/ipmj/java/partmagn/ Java demo mirror/ipmj/java/partmagn/ mirror/ipmj/java/partmagn/ mirror/ipmj/java/partmagn/ Cosmic and Heliospheric Learning Center Cosmic and Heliospheric Learning Center Astronomy Picture of the Day Astronomy Picture of the Day

9/16/03Prof. Lynn Cominsky51 Web Resources History of cosmic rays History of cosmic rays Pierre Auger Observatory Pierre Auger Observatory Adelaide Astrophysics Group new.html Adelaide Astrophysics Group new.html new.html new.html AGASA AGASA HIRES HIRES