dark matter, dark energy, and the current state of cosmology nick kaiser institute for astronomy...

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?