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…