Dark Matter, Dark Energy, and the Current State of Cosmology
Nick Kaiser
Institute for Astronomy
University of Hawaii
Fritz Zwicky
The Coma Cluster
Zwicky & the Missing Mass
• Measured galaxy speeds in Coma
• Virial theorem: M/L ~ 500 M_sun/L_sun
• The “missing mass”
• An outstanding problem in cosmology– 90-98% of the universe is in a mysterious form– detectable only by its gravitational attraction
The Dark Matter Puzzle
• Where is it?
• How much is there?
• What is it?
Cosmology in a nutshell:
• The old cosmology– Friedmann; Einstein; de Sitter ….
• The New Cosmology– Inflation - scalar fields
• The Hot Big Bang
• Structure Formation
The Friedmann Model
• Scale factor R(t)• mass density and
curvature of space• problems
– horizon
– flatness
Inflationary Cosmology• In the beginning there was the field….
• Vector, tensor and scalar fields
• Weinberg-Salaam:– unified theory - the Higgs field
• The “inflaton”– central to inflation– solves the old problems– predicts a flat universe =1– quantum fluctuations structure formation
The Hot Big Bang
• The cosmic kitchen– big bang nucleosynthesis
• Abundance of “baryons” baryons ~ 0.02
• Relics– cosmic background– neutrinos
Structure Formation• Quantum fluctuations
• gravitational instability
• dark matter
• the “cosmic web”
The Cosmic Web
The history of the Universe
Inventory of Dark Matter
• Galaxies– luminous parts M/L ~ 1-5– flat rotation curves M/L ~ 30
• Pairs … Groups … Clusters– M/L ~ 100-500
• Super-Cluster Dynamics = 1?
Galaxies
Gravitational Lensing
• Gravity bends light rays– probe of dark matter– highly versatile
• microlensing - “machos”
• galaxy lensing
• lensing by cluster
• lensing by superclusters
Theory of gravitational lensing
Lensing by galaxies
Lensing by clusters
MACSJ2243
Cosmic Microwave Background
• Relic from the big bang
• Probe of structure @ t ~ 100,000 yr
• COBE– large angle
• BOOMERANG– small angles– flat Universe
COBE Satellite
The COBE Sky
From COBE to BOOMERANG
The Universe is flat!
What is the Matter?
• Neutrinos?– No longer popular
• Axions or other fields?
• WIMPs?
• Etc etc etc….
• Plenty of theory - scarce observations
Dark Energy
• Consensus model: ~ 0.3
• CMB = 1
• resolution: the accelerating Universe– expansion history from supernovae– fainter than expected– universe is being accelerated - dark energy– “late time inflation” - yet another field?
The Nearest GalaxiesThe Nearest GalaxiesLMC
SMC
February 22, 1987February 22, 1987
Expansion History from SN
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The Current Status of Cosmology
• A “working model” for creation of the Universe and the structure therein
• Impressive concordance with current observations
• Embarrassing number of ingredients– luminous baryons; dark baryons; neutrinos;
dark matter; dark energy….
• Epicycles?