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Seeing the Invisible
Prof. Lynn CominskySonoma State University
Director, Education and Public Outreach
Sources of light
• Which of these things are sources of light?
• If things are not emitting light, how do you see them?
Seeing the light
• Do you know of any type of light that is not visible to your eyes?
• Are people sources of light?
Have you ever seen the invisible?
How do you detect light?
• What are common light detectors for– Visible light?– Infrared light?– X-ray light?
• Radio transmission towers• TV transmission towers
• Cold objects• Planets• Collapsed stars• Radio galaxies• Intergalactic matter
Radio
• microwave generator in ovens
• warm molecular clouds• Planets• Galaxies• The Universe!
Microwave
• warm objects • People• Ovens
• Planets• “Normal” stars• Protostars• Galaxies
Infrared
• hot objects (thousands of degrees)• Sun• Lightbulbs
• Planets• “Normal” stars, sun-like and hotter• Galaxies
Visible
• hotter objects (10,000 to about 100,000 Kelvin)• UV lights (“black lights”)
• Nebulae• Aurorae• Hot stars• Galaxies
Ultraviolet
• very hot objects (millions of degrees)• X-ray generators
• Solar corona• Pulsars• Black holes• Galaxy clusters
X-rays
Electronic light detectors
• Solid state devices that detect individual light particles (“photons”)
Digital dental x-ray
Do you know of any others?
What you can see from the Earth
VLA WMAP Spitzer FUSE Chandra Fermi
Why study the extreme Universe?
• Universe as seen by eye is peaceful
The Fermi mission…• First space-based collaboration
between astrophysics and particle physics communities
• International partners from France, Germany, Italy, Japan & Sweden
• Launched June 11, 2008• Expected duration 5-10 years
Before launch
• Large Area Telescope
• Gamma-ray
Burst Monitor
Large Area Telescope (LAT)• PI Peter Michelson (Stanford)• International Collaboration: USA NASA
and DoE, France, Italy, Japan, Sweden
• LAT is a 4 x 4 array of towers
• Each tower is a pair conversion telescope with calorimeter
Pair-conversion
• Anti-matter partners of e- are positrons (e+)
• When they meet, they annihilate each other!
E = mc2
m = mass of the electron or positron
E = energy of gamma ray
Now in reverse….
This process is called “pair conversion” as the incoming gamma-ray converts into an electron/positron pair
tungsten
How does the LAT work?
• Anticoincidence Detectors – screen out charged particles
• Tungsten converts gamma rays into e+ e- pairs
• Calorimeter measures total energy
Launched!
• June 11, 2008
• Delta II Heavy (9 solid rocket boosters)
• Mass is 4300 kg
• 555 km circular orbit
• 1500 W total power
• 40 Mb/sec downlink
What the sky looks like in gamma rays
What types of things emit gamma rays?
• Really big lightning storms• Our Sun when it flares• Our Milky Way galaxy – charged particles
hitting gas between the stars• Huge explosions of stars that are dying (some
make collapsed stars)• Collapsed stars sending out jets of charged
particles• Black holes sending out jets of charged
particles
Gamma-ray bursts on the sky
• About 4-5 bursts per week
Typical strong GRB seen by GBM
• Each burst has as much energy as our Sun puts out in its entire lifetime
Gamma-ray Jets from Black Holes• Jets flare
dramatically in gamma rays
• Galaxies that point their jets at us are called “blazars”
• How do the black holes send out jets?
Art by Aurore Simonnet
Gamma rays from pulsars
• Collapsed stars – size of San Francisco, mass of our Sun
• Sending out beams of particles like lighthouses
What is the Universe made of?
• Matter – what we experience in our everyday lives
• Dark matter – you can’t see it but you can feel it
• Dark Energy – a mysterious force that is tearing the Universe apart
Searching for dark matter
• Dark matter makes up 80% of the matter in the Universe
• The leading particle candidate for dark matter is a “WIMP” =weakly interacting massive particle
• Fermi could see gamma rays from WIMPS annihilating with each other
• More gamma rays are expected near the center of our Galaxy
Many places to look!
All-sky map of simulated gamma ray signal from DM annihilation (Baltz
2006)
Satellite Galaxies
Galactic Center
Milky Way Halo
Spectral Lines Extra-galactic
31
No detections so far, but the search continues…