Dark Matter in the Universe:
MACHOS, WIMPS and
Little White Dwarfs
University of Chicago
What does our Universe look like?
What is it made of?
How old is it?
How will it end?
Where do we fit into this picture?
An ancient and still current
What is the Universe
Where is the matter?
! Most of the matter in the Universe is
unseen (dark matter)
! Most of this dark matter is in the form of
exotic new particles
! But we haven’t found most of the
ordinary matter either -- where is it?
Basically, we detect dark matter via its gravitational
effects on something else.
1st evidence for dark matter: Zwicky (1930s)
Coma Cluster of galaxies
Now have evidence on many scales, from the rotation
curves of over 1000 spiral galaxies to gravitational
lensing of clusters of galaxies
Weighing the Universe:
ρ= mass-energy density of Universe
ρc = critical density
Ω = ρ/ρc
Ω < 1 OPEN
Ω = 1 FLAT
Ω > 1 CLOSED
News Headlines in 2000:
The Universe is FLAT!
Density of matter/energy in Universe
is equal to the critical density
I. Luminous Matter:
Less than 1% of Universe
is in visible matter!
z=2~4 Ωbaryons =
Ωstars = 0.0035
Ωgas/galaxies = 0.0006
z∼1100 Ωbaryons = 0.04
Ωgas/clusters = 0.0025
II. Ordinary (baryonic) Matter:
Big Bang Nucleosynthesis
Theory of the formation of the light elements (Deuterium,
Helium, Lithium) in the early Universe (about 1 minute after
the Big Bang) predicts the observed abundances of these
~5% of the Universe is in
Inventory of the Universe
! Matter in stars & gas (galaxies) < 1%
! Ordinary (baryonic) matter 5%
→most of the ordinary matter is “dark”
III. Total Matter:
Observations of Clusters of
~ 35% of Universe in Matter
Weighing a Cluster of Galaxies:
Searching for Dark Matter
in our Galaxy:
Milky Way Galaxy
Typical Spiral Galaxy with a disk, central bulge,