1. Dark Matter

2. Dark Matter Dark Energy
There is a lot of matter in the Universe that we can’t see
Dark Energy
The name given to the energy causing the Universe to expand, whatever it may be
Einstein called it the “Cosmological Constant”

4. Dark Matter in Spiral Galaxies
Construct rotation curves for other galaxies using HI clouds
External galaxies also show flat curves
Mass-to-light ratios show that dark matter is 10x more abundant the luminous matter

5. Dark Matter in Elliptical Galaxies
Rotation curves not possible in ellipticals
No HI gas
No disk
Look at width of absorption lines
Due to superposition of different doppler shifts
Velocity appears to stay the same to large radii, similar to flat rotation curve in spirals

6. Dark Matter in Galaxy Clusters
Evidence for dark matter from:
Orbits of galaxies
Hot intracluster gas temperatures
Gravitation lensing

7. Orbits Mass determined from orbital motions
Mass determined from luminosity
Two masses are very different
MOrbit > 10Mlum
Dark matter must outweight normal matter by at least 10x

8. Intracluster Gas
Temperature of gas tells us the total mass of the galaxy cluster
Gas is in gravitational equilibrium
Strength of gravity requires T~107 K
Emits X-rays
Mcluster >> Mgas

9. Gravitational Lensing
Gravitational well due to mass of cluster bends light passing near cluster
The more mass in the cluster, the more the light is bent

11. Gravitational Lensing
Gravitational well due to mass of cluster bends light passing near cluster
The more mass in the cluster, the more the light is bent
Not enough luminous matter to bend light as much as observed

12. Dark matter makes up ~90% of the Universe
Current theory suggests WIMPs as candidate dark matter particles
MaCHOs no longer really accepted

13. Large Scale Structure of the Universe

14. Development of Structure
Dark matter crucial to the development of structure
Normal matter is not nearly abundant enough
Gravity pulls dark matter into clumps

15. Development of Structure
Over time, matter forms filaments and bigger clumps, which are the homes of galaxy clusters