Transcript What is the dark matter?

All but 4 percent:
Dark Matter and Dark Energy
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Our story begins in 1933…
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The Coma Cluster of Galaxies and
Astronomer Fritz Zwicky
Slow down –
You move too fast!
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The Coma Cluster of Galaxies and
Astronomer Fritz Zwicky
Why don’t
you fly apart?
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The Coma Cluster of Galaxies and
Astronomer Fritz Zwicky
If the Stars
don’t weigh
enough…
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The Coma Cluster of Galaxies and
Astronomer Fritz Zwicky
Then something
else does!
Dark Matter!
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40 years later, Vera Rubin shows
galaxies spin too fast to hold together…
Measuring spectra of galaxies
to infer velocity from Doppler
shifts (c. 1970)
Stars and gas rotate with
speed V around the center of
NGC 3198
(Image from Begeman 1989)7
…unless held together by dark matter!
GM(r)=rVc2(r)
Luminous galaxy
Dark
matter
Embedded in
cloud of dark matter
Credits:
Although diffuse, dark matter
is crucial for galaxy formation
Left: J. Kormendy (NGC 4216).
Right: K. Begeman (NGC 3198) and
K. Freeman
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Recipe for our Universe!
Photons: 0.03%
Neutrinos: 0.3%
Atoms: 4%
Dark Matter: 23%
Dark Energy: 73%
Credit: NASA/GSFC
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4% does
not gain
admission
to this
show!
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What is the dark matter?
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What is the dark matter?
Not electrons, protons, or neutrons,
even if they do not “shine” as stars
(nuclear fusion in the early universe would
drastically overproduce Helium)
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What is the dark matter?
Not known elementary
particles or
combination
thereof
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Our best guess for the dark matter
since 1977:
A new elementary particle
generically called a
Weakly Interacting Massive Particle,
or
WIMP
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How will we test this hypothesis?
Produce it in high-energy particle physics
collisions
Simulated production of
neutralino WIMP at a future
International Linear Collider
(c. 2025)
Credit: Norman Graf, SLAC
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How will we test this hypothesis?
Watch it annihilate with anti-matter
NASA/DOE Fermi GammaRay Space Telescope and
other satellite and balloon
experiments looking for this
now!
Image credit: Sky & Telescope/
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Gregg Dinderman
How will we test this hypothesis?
When it hits us, we will know it (or will we?)
Many laboratory
experiments are
searching for atomic
recoil from WIMP
collisions.
Image credit: Discover/
Michael Attisha
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When a WIMP hits
me, I’ll know it…
Cryogenic Dark Matter Search
detector element in deep
freeze (0.1 K), ½-mile
underground in Soudan, MN
This experiment has not seen
WIMPS yet, but has placed the
best current limits on their
properties if they exist.
See Technology Review May/June 2009!
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But wait, there’s more!
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A Strange Universe
Why are distant galaxies accelerating away from us?
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How to
describe the expanding
Galaxies rushing apart on their own
universe
Stretching of space
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Imagine a repulsive force that grows
with distance between every pair of atoms
What would happen?
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Co-Discoverer of Cosmic Acceleration
Johns Hopkins Professor
MacArthur Award Winner
Adam Riess
MIT SB 1992
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A cancer has taken over the cellular
machinery of space!
Linder 2008 Scholarpedia
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What is the cosmic carcinogen?
1. Einstein’s Cosmological Constant
added to his theory of gravity – revoked, and…
…resurrected by modern physics as quantum
fluctuations of the vacuum.
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What is the cosmic carcinogen?
2. Exotic new forms of energy, Dark Energy,
behaving similarly to the quantum vacuum.
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What is the cosmic carcinogen?
3. Maybe Einstein’s
theory of gravity is
wrong.
Phillip Zukin, physics
graduate student
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What is the cosmic carcinogen?
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How can we find out?
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Study the growth of
cosmic structure
after the big bang –
gravity writes
history.
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