9/16/03prof. lynn cominsky1 class web site: lynnc/courses/a305 office: darwin 329a and nasa e/po...

9/16/03 Prof. Lynn Cominsky 1

Class web site: Class web site: http://http://glastglast

.sonoma.edu/~lynnc/courses/a305.sonoma.edu/~lynnc/courses/a305

Office: Darwin 329A and NASA E/POOffice: Darwin 329A and NASA E/PO

(707) 664-2655(707) 664-2655

Best way to reach me: Best way to reach me: [email protected]@charmian.sonoma.edu

Astronomy 305/Frontiers in Astronomy 305/Frontiers in AstronomyAstronomy


What is the origin of cosmic What is the origin of cosmic rays?rays?

Discovery of Cosmic Rays Discovery of Cosmic Rays General properties of cosmic raysGeneral properties of cosmic rays Cosmic rays from the SunCosmic rays from the Sun Accelerating Cosmic rays Accelerating Cosmic rays Detecting cosmic raysDetecting cosmic rays The highest energy cosmic raysThe highest energy cosmic rays New cosmic ray experimentsNew cosmic ray experiments


Types of RadiationTypes of Radiation We have discussed electromagnetic We have discussed electromagnetic

radiation aka light – massless, travel at v=cradiation aka light – massless, travel at v=c When scientists first started studying When scientists first started studying

radiation in the early 1900s, they found 3 radiation in the early 1900s, they found 3 different types of rays different types of rays Alpha rays – turned out to be Helium nucleiAlpha rays – turned out to be Helium nuclei Beta rays – turned out to be electrons and Beta rays – turned out to be electrons and

positronspositrons Gamma rays – turned out to be lightGamma rays – turned out to be light

Detectors invented to study radiation Detectors invented to study radiation included Geiger counters, film and included Geiger counters, film and electroscopeselectroscopes


Discovery of Cosmic RaysDiscovery 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 Viktor Hess (1912) takes electroscope on a balloon flight to 17,500 feet on a balloon flight to 17,500 feet (without oxygen!)(without oxygen!)


Hess’ ExperimentHess’ Experiment

Hess used an electroscope – detects Hess used an electroscope – detects charge on 2 thin filmscharge on 2 thin films

http://www.shep.net/resources/curricular/http://www.shep.net/resources/curricular/physics/P30/Unit2/electroscope.htmlphysics/P30/Unit2/electroscope.html

When the cosmic rays hit the When the cosmic rays hit the electroscope, they carried away chargeelectroscope, they carried away charge

More cosmic rays More cosmic rays electroscope would electroscope would discharge fasterdischarge faster

Hess won the Nobel prize in 1936 for his Hess won the Nobel prize in 1936 for his discovery of cosmic raysdiscovery of cosmic rays


What are cosmic rays?What are cosmic rays?

Cosmic rays are charged particles Cosmic rays are charged particles such as protons, electrons and such as protons, electrons and nuclei of atomsnuclei of atoms

They are NOT electromagnetic They are NOT electromagnetic radiation (aka light)radiation (aka light)

However, sometimes cosmic rays However, sometimes cosmic rays interact with gas in our galaxy to interact with gas in our galaxy to make gamma raysmake gamma rays


High energy Gamma-ray High energy Gamma-ray mapmap

Gamma rays in the plane of the galaxy made from cosmic rays hitting gas


Composition of cosmic raysComposition of cosmic rays Cosmic rays are made of nuclei of Cosmic rays are made of nuclei of

different elements (and also electrons)different elements (and also electrons) The percentage of each element of The percentage of each element of

different types is called “composition”different types is called “composition” All the nuclei of the elements in the All the nuclei of the elements in the

periodic table are present in cosmic rays periodic table are present in cosmic rays The composition of cosmic rays is about The composition of cosmic rays is about

the same as that of the elements in the the same as that of the elements in the solar systemsolar system

Various isotopes of elements are also Various isotopes of elements are also detected though harder to distinguishdetected though harder to distinguish


ACEACE Advanced Composition ExplorerAdvanced Composition Explorer http://www.srl.caltech.edu/ACE/http://www.srl.caltech.edu/ACE/ Launched 8/25/97, still operationalLaunched 8/25/97, still operational Stays near L1 point in Earth-Sun OrbitStays near L1 point in Earth-Sun Orbit Studies particles in solar wind, interplanetary Studies particles in solar wind, interplanetary

medium, interstellar medium and galactic mattermedium, interstellar medium and galactic matter


Properties of cosmic raysProperties of cosmic rays

90% of cosmic rays are hydrogen 90% of cosmic rays are hydrogen nuclei (aka protons) nuclei (aka protons)

9% are helium nuclei9% are helium nuclei 1% are all the other elements1% are all the other elements Thousands of low-energy cosmic Thousands of low-energy cosmic

rays hit every square meter of the rays hit every square meter of the Earth each secondEarth each second

High energy cosmic rays are rare – High energy cosmic rays are rare – less than 1 per kmless than 1 per km22 per century per century


Charged particle in magnetic Charged particle in magnetic fieldfield

http://webphysics.ph.msstate.edu/jhttp://webphysics.ph.msstate.edu/javamirror/ipmj/java/partmagn/avamirror/ipmj/java/partmagn/

Magnetic fields change the Magnetic fields change the direction of travel of charged direction of travel of charged particles (opposite effect for particles (opposite effect for positive vs. negative particles)positive vs. negative particles)

Since the paths of cosmic rays are Since the paths of cosmic rays are changed as they travel through changed as they travel through space, it is difficult to figure out space, it is difficult to figure out where they originatedwhere they originated


Cosmic rays vs. gamma Cosmic rays vs. gamma raysrays Cosmic rays (1) Cosmic rays (1)

are deflected by are deflected by magnetic fields magnetic fields in spacein space

Gamma rays (2) Gamma rays (2) travel in straight travel in straight lines, unaffected lines, unaffected by magnetic by magnetic fields fields


Cosmic ray spectrumCosmic 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


Solar flares make low energy CRsSolar flares make low energy CRs

Solar flares originate in sunspotsSolar flares originate in sunspots Magnetic field in sunspots stores Magnetic field in sunspots stores

energy than is released in solar flaresenergy than is released in solar flares Sunspots often occur in pairs or groupsSunspots often occur in pairs or groups The more complex the groups, the The more complex the groups, the

greater probability of a resulting flaregreater probability of a resulting flare A large flare has 10A large flare has 1066 times more energy times more energy

than a large earthquakethan a large earthquake


Solar FlaresSolar Flares

Solar prominence seen by Skylab in 1973

SOHO/MDI 11th magnitude

earthquake on Sun following solar flare


Solar Activity CycleSolar Activity Cycle Every 11 years, Every 11 years,

sunspots and sunspots and X-rays increaseX-rays increase

Increased Increased radiation radiation causes Earth’s causes Earth’s atmosphere to atmosphere to expandexpand

Solar flares Solar flares cause radio cause radio interferenceinterference 1991

1995


Space WeatherSpace Weather

For the latest on Space Weather, For the latest on Space Weather, including solar flares, aurorae, including solar flares, aurorae, blackouts, and sunspots, see blackouts, and sunspots, see http://www.sec.noaa.gov/SWN/http://www.sec.noaa.gov/SWN/

We are just past Solar Max 23!


Coronal Mass EjectionsCoronal Mass Ejections

CMEs are the cause of major CMEs are the cause of major geomagnetic storms on Earthgeomagnetic storms on Earth

CMEs are NOT caused by solar flares, CMEs are NOT caused by solar flares, although they may both be signatures of although they may both be signatures of rapid changes in the magnetic fieldrapid changes in the magnetic field

10101515 - 10 - 1016 16 g of material is ejected into g of material is ejected into space at speeds from 50 to >1200 km/sspace at speeds from 50 to >1200 km/s

Can only be observed with coronagraphsCan only be observed with coronagraphs


Coronal Mass EjectionsCoronal Mass EjectionsCoronal mass ejection in UV from SOHO

Solar Maximum Mission CME in 1989


Solar flares affect the EarthSolar flares affect the Earth Light in solar flares travels at the Light in solar flares travels at the

speed of light (8.5 minutes to reach speed of light (8.5 minutes to reach Earth)Earth)

Relativistic particles travel at near Relativistic particles travel at near light speed – arrive in 20 minutes to light speed – arrive in 20 minutes to hourshours

Bulk material ejected from Sun travels Bulk material ejected from Sun travels at 400-1000 km/hour – takes ~1 day at 400-1000 km/hour – takes ~1 day to reach Earthto reach Earth

Charged particles that hit the Earth Charged particles that hit the Earth create auroraecreate aurorae


AuroraeAurorae Best observed near the magnetic polesBest observed near the magnetic poles Colors are due to different molecules at Colors are due to different molecules at

different heights in the Earth’s different heights in the Earth’s atmosphere – mostly oxygen and nitrogenatmosphere – mostly oxygen and nitrogen

Recent auroral location


South Atlantic Anomaly and CRsSouth Atlantic Anomaly and CRs

Region where the Earth’s magnetic field Region where the Earth’s magnetic field dips that allows CRs to reach lower into dips that allows CRs to reach lower into the atmospherethe atmosphere


Medium-energy Cosmic RaysMedium-energy Cosmic Rays 101012 – 10 – 1015 eV eV Composition at Earth’s atmosphere Composition at Earth’s atmosphere

50% protons50% 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 Believed to originate outside of solar system but inside of Milky solar system but inside of Milky Way galaxyWay galaxy


Possible Sources of Galactic CRsPossible Sources of Galactic CRs

Energetic places in the Galaxy Energetic places in the Galaxy Black HolesBlack Holes Neutron starsNeutron stars PulsarsPulsars SupernovaeSupernovae

30 Doradus star forming

region

Red = Xrays

Blue = UV

Green = ionized H


Accelerating cosmic raysAccelerating cosmic rays

Medium energy cosmic rays must be Medium energy cosmic rays must be accelerated by shock waves in our galaxyaccelerated by shock waves in our galaxy

Much research is going on to conclusively Much research is going on to conclusively prove that supernovae can accelerate prove that supernovae can accelerate cosmic rays to medium energiescosmic rays to medium energies

Supernovae are believed to be able to Supernovae are believed to be able to accelerate CRs up to the energy of the accelerate CRs up to the energy of the “knee” 3 x 10“knee” 3 x 101515 eV eV

How do we prove that supernovae are How do we prove that supernovae are really the acceleration sites for CRs?really the acceleration sites for CRs?


ASCA X-ray Astronomy satelliteASCA X-ray Astronomy satellite

ASCA = ASCA = Advanced Advanced Satellite for Satellite for Cosmology and Cosmology and Astrophysics aka Astrophysics aka Asuka or flying Asuka or flying birdbird

Japanese X-ray Japanese X-ray astronomy astronomy satellite that satellite that observed 1993-observed 1993-20012001


ASCA and SN1006ASCA and SN1006


ASCA and SN1006ASCA and SN1006

First direct evidence that supernovae First direct evidence that supernovae can accelerate cosmic rayscan accelerate cosmic rays

Non-thermal synchrotron spectrum at Non-thermal synchrotron spectrum at the edges of the supernova where the the edges of the supernova where the shocks should occurshocks should occur

Thermal spectrum in the center of the Thermal spectrum in the center of the supernova due to hot gas from explosionsupernova due to hot gas from explosion

Magnetic field in SN1006 exactly the Magnetic field in SN1006 exactly the right strength to accelerate CRs up to right strength to accelerate CRs up to the “knee”the “knee”


Detecting cosmic raysDetecting cosmic rays

Cosmic rays are further classified into Cosmic rays are further classified into primaries and secondariesprimaries and secondaries

Primaries are the particles which hit the Primaries are the particles which hit the Earth’s atmosphereEarth’s atmosphere

Secondaries are created by interactions Secondaries are created by interactions between the primaries and the air between the primaries and the air molecules molecules


Air showers of secondary CRsAir showers of secondary CRs

Secondaries are primarily “pions” –Secondaries are primarily “pions” –elementary particles with charge + - or 0elementary particles with charge + - or 0

Charged pions hit other air molecules Charged pions hit other air molecules Neutral pions decay into 2 gamma rays Neutral pions decay into 2 gamma rays

which then create positron/electron pairswhich then create positron/electron pairs Cascade includes UV fluorescent Cascade includes UV fluorescent

emission, more charged particles and emission, more charged particles and Cerenkov radiation – blue light caused by Cerenkov radiation – blue light caused by very fast particles moving through the very fast particles moving through the atmosphere at faster than the local speed atmosphere at faster than the local speed of lightof light


Air showers of secondary CRsAir showers of secondary CRs


Shower maximumShower maximum

Cascade continues until average particle in the Cascade continues until average particle in the shower is not energetic enough to create new shower is not energetic enough to create new particles particles “shower maximum” “shower maximum”

After shower maximum, particles are absorbed After shower maximum, particles are absorbed by atmospheric molecules and shower by atmospheric molecules and shower intensity decreasesintensity decreases

Shower maximum: for each 1 GeV energy in Shower maximum: for each 1 GeV energy in primary cosmic ray, shower has 1-1.6 particlesprimary cosmic ray, shower has 1-1.6 particles

For primaries > 10For primaries > 101515 eV, enough particles eV, enough particles reach ground to be detected in detector arrayreach ground to be detected in detector array


Extensive air shower arraysExtensive air shower arrays ““Footprint” of Footprint” of

shower extends shower extends several hundred several hundred square meterssquare meters

Particles are Particles are traveling at speeds traveling at speeds near cnear c

By comparing arrival By comparing arrival times at different times at different detectors, direction detectors, direction of origin can be of origin can be determined within 1determined within 1oo


Air Cerenkov telescopesAir Cerenkov telescopes

Cerenkov light is Cerenkov light is imaged onto segmented imaged onto segmented optical light telescopesoptical light telescopes

Showers initiated by Showers initiated by gamma rays with gamma rays with E>TeV can be E>TeV can be distinguished from CR distinguished from CR showers by analyzing showers by analyzing the shape of the shower the shape of the shower profileprofile


Ultra-high energy cosmic raysUltra-high energy cosmic rays

Believed to originate outside of our Believed to originate outside of our Galaxy but perhaps in the local groupGalaxy but perhaps in the local group

For CRs above the “knee” (>3 x 10For CRs above the “knee” (>3 x 101515 eV) eV) some other acceleration process must some other acceleration process must occuroccur

Jets from active galaxies are often Jets from active galaxies are often theorized to be the acceleratorstheorized 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?


Air “Fluorescent” DetectorsAir “Fluorescent” Detectors

UV light flashes emitted from (mostly) UV light flashes emitted from (mostly) Nitrogen molecules are focused and Nitrogen molecules are focused and imaged with detectors on telescopesimaged with detectors on telescopes

NOTE: UV light is really scintillation not fluorescence – which is remission at visible light of UV light


Fly’s Eye Detector Array in UtahFly’s Eye Detector Array in Utah


Fly’s Eye: 1981-1993Fly’s Eye: 1981-1993

Pixels on sky from telescope array Pixels on sky from telescope array are hexagonal tiles like a fly’s eye are hexagonal tiles like a fly’s eye – eventually a second array was – eventually a second array was built for stereo visionbuilt for stereo vision

movie


Akeno Giant air shower arrayAkeno Giant air shower array

AGASA is in JapanAGASA is in Japan 111 surface detectors 111 surface detectors

and 27 muon and 27 muon detectors under detectors under ground in 100 kmground in 100 km22 separated by 1 kmseparated by 1 km

Combining muon and Combining muon and surface detectors surface detectors yields composition of yields composition of primary cosmic rayprimary cosmic ray


ScintillatorsScintillators Large pieces of material (usually Large pieces of material (usually

inorganic salts or organic plastics) that inorganic salts or organic plastics) that emit visible light when hit by CRsemit visible light when hit by CRs

Often used for gamma rays as wellOften used for gamma rays as well

AGASA Scintillato

r


Muon DetectorsMuon Detectors

Many of the secondaries are muons – Many of the secondaries are muons – negatively charged particles that are negatively charged particles that are cousins to electrons but 186 times more cousins to electrons but 186 times more massivemassive


Water Cerenkov DetectorsWater Cerenkov Detectors Tanks of water surrounded with Tanks of water surrounded with

photo-multipliers to detect the blue photo-multipliers to detect the blue Cerenkov light emitted in the Cerenkov light emitted in the waterwater

AGASA Water

Cerenkov Detector


AGASA highest energy eventAGASA highest energy event 3 x 103 x 102020 eV – eV –

second highest second highest energy cosmic ray energy cosmic ray ever detectedever detected

Shower spread Shower spread over 6 x 6 kmover 6 x 6 km22

Billions of particles Billions of particles in showerin shower

Primary probably Primary probably an oxygen nucleus an oxygen nucleus or similar elementor similar element


AGASA anisotropyAGASA anisotropy

CRs greater than 10CRs greater than 101919 eV seen in 11 eV seen in 11 years of observations with AGASAyears of observations with AGASA

Red are > 10Red are > 102020 eV, green are 4-10 x 10 eV, green are 4-10 x 101919 eVeV

Circles are clusters of events within 2.5Circles are clusters of events within 2.5oo


AGASA data – “ankle” to GZK AGASA data – “ankle” to GZK cutoffcutoff

>10>102020 eV energy eV energy CRs from > 150 CRs from > 150 million light million light years away years away should not should not reach the Earth reach the Earth due to collisions due to collisions with the with the photons in the photons in the microwave microwave background background “GZK cutoff”“GZK cutoff”


Pierre Auger Observatory Pierre Auger Observatory (being (being built)built)

2 water Cerenkov arrays to detect the 2 water Cerenkov arrays to detect the highest energy cosmic rays – one each in the highest energy cosmic rays – one each in the northern and southern hemispheresnorthern and southern hemispheres

Each location occupies 3000 kmEach location occupies 3000 km22 and has and has 1600 detectors1600 detectors

UtahArgentina


Pierre Auger Observatory Pierre Auger Observatory (Argentina)(Argentina)

30 detectors are now operational (out of 30 detectors are now operational (out of 1600 planned)1600 planned)

2 fluorescence detectors are working 2 fluorescence detectors are working (out of 24 planned)(out of 24 planned)

A building housing a fluorescence detector


Why should we care about CRs?Why should we care about CRs?

We are constantly exposed to background We are constantly exposed to background radiation from secondary CRsradiation from secondary CRs

Exposure is greater in airplanes, mountainsExposure is greater in airplanes, mountains CRs produce CCRs produce C1414 used for carbon dating used for carbon dating CRs produce single-event-upsets CRs produce single-event-upsets

(mistakes) in space-based computer chips(mistakes) in space-based computer chips We want to understand how nature can We want to understand how nature can

accelerate particles to near light speedaccelerate particles to near light speed Highest energy CRs could signify new Highest energy CRs could signify new

physicsphysics


ASPIRE lab on cosmic raysASPIRE lab on cosmic rays Go to Go to

http://sunshine.chpc.utah.edu/javalhttp://sunshine.chpc.utah.edu/javalabs/java102/hess/index.htmabs/java102/hess/index.htm

Try at least the Hess’ balloon ride Try at least the Hess’ balloon ride (Activity 1). Be sure to integrate (Activity 1). Be sure to integrate counts for at least 20 seconds. counts for at least 20 seconds. What do you conclude about the What do you conclude about the origin of cosmic rays?origin of cosmic rays?

Also try activities 2, 3 and 4 if you Also try activities 2, 3 and 4 if you have time.have time.


Web ResourcesWeb Resources Imagine the Universe Imagine the Universe

http://imagine.gsfc.nasa.http://imagine.gsfc.nasa.govgov Java demo Java demo

http://webphysics.ph.msstate.edu/jhttp://webphysics.ph.msstate.edu/javamirror/ipmj/java/partmagn/avamirror/ipmj/java/partmagn/

Cosmic and Heliospheric Learning Cosmic and Heliospheric Learning Center http://helios.gsfc.nasa.govCenter http://helios.gsfc.nasa.gov

Astronomy Picture of the Day Astronomy Picture of the Day http://antwrp.gsfc.nasa.gov/apod/http://antwrp.gsfc.nasa.gov/apod/


Web ResourcesWeb Resources History of cosmic rays History of cosmic rays

http://ast.leeds.ac.uk/haverah/cosrays.shtmlhttp://ast.leeds.ac.uk/haverah/cosrays.shtml

Pierre Auger ObservatoryPierre Auger Observatory http://www.auger.org/http://www.auger.org/

Adelaide Astrophysics Group Adelaide Astrophysics Group http://www.physics.adelaide.edu.au/astrophysihttp://www.physics.adelaide.edu.au/astrophysics/cr_new.htmlcs/cr_new.html

AGASAAGASA http://www-akeno.icrr.u-tokyo.ac.jp/AGASA/http://www-akeno.icrr.u-tokyo.ac.jp/AGASA/

HIRESHIRES http://hires.physics.utah.edu/ http://hires.physics.utah.edu/

9/16/03prof. lynn cominsky1 class web site: lynnc/courses/a305 office: darwin 329a and nasa e/po...

Documents

cosmic rays electroscope

origin of cosmic rays

discovery of cosmic

nuclei of atoms cosmic

light gamma rays

positrons gamma rays

positrons beta rays

helium nuclei alpha