Dark Matter Dark Energy (quintessence, cosmological
constant)
Galaxy rotation curves show unseen matter
How to measure spiral galaxy rotation curves
Matter as much as 10x further than luminous galaxy
Elliptical use velocity dispersion – broadened lines
About 90% dark matter
Clusters
Mass from motion of galaxies in clusters shows large mass-to- light ratio
About 90% dark matter
Hot x-rays from intracluster gas visible x-ray show dark matter
[temperature of gas related to gravity in cluster]
Gravitational lenses
Einstein gravitational lenses movie –in this case clusters of galaxies 1 2
But what IS it?
Ordinary dark matter [baryonic] MACHOs (massive compact halo objects) light curve
These are detected but they do not make up much dark matter.
Non baryonic matter can be hot (neutrinos) or cold (cold dark matter)
Whatever this is it will affect how ordinary matter clumps.
Structure
Clusters and groups near each other do not expand at the Hubble rate. They are “gravitationally bound” (as is everything inside the cluster)
The gravity gives structure to the universe clusters, superclusters, walls, voids
The large scale structure is uniform. The lumps can be modeled 1 2
Hubble expansion: will it go on forever?
Does the kinetic energy (expansion) exceed the potential energy (gravity)
or expansion velocity vs. density critical density is 10-29g/cm3
Luminous matter not anywhere close
Add dark matter you get near 30% of the critical density.
If gravity ONLY
Recollapsing density larger than critical Big Crunch closed universe
Critical density equal critical –just barely expands forever flat universe
Coasting density less than critical – plenty of energy to expand forever open universe
With a repulsive force
Accelerating repulsive force keeps expansion going faster and faster
Evidence from white dwarf supernovae indicate acceleration
Cosmological constant, Dark energy, etc.
What is the Universe made of?
