1. A105 Stars and Galaxies Today’s APOD This week’s units: just 80
Quiz online this week – Original Test and Survey Tool
Projects due Nov. 30

2. DARK MATTER
The universe is NOT what it seems…

3. DARK MATTER
“Extraordinary claims require extraordinary evidence.” (Carl Sagan)
“Extraordinary claims require extraordinary proof.” (Marcello Truzzi)
“The weight of evidence for an extraordinary claim must be proportioned to its strangeness” (Laplace)
“A wise man, therefore, proportions his belief to the evidence” (David Hume)

4. Evidence for Dark Matter
Rotation of galaxies
Velocities of stars in galaxies
Gravitational lensing
Velocities of galaxies in clusters

5. Mass within Sun’s orbit:
1.0 x 1011 MSun
Total mass:
~1012 MSun

6. What’s the PROBLEM???
The orbits of stars suggest that galaxies contain several times more mass that we can find in stars, gas and dust
MISSING MASS!
Dark matter is the material believed to account for the discrepancy between the mass of a galaxy as found from the orbits of stars and the mass observed in the form of gas and dust

7. The visible portion of a galaxy lies deep in the heart of a large halo of dark matter

8. Galaxy interactions require more mass than we can see
Computer
simulation
The real
thing
Antennae Galaxy (HST)

9. Evidence for dark matter in clusters of galaxies
We can measure the velocities of galaxies in a cluster from their Doppler shifts
The mass we find from galaxy motions in a cluster is about 50 times larger than the mass in stars!

10. Exploring the Dark Universe with Gravitational Lenses

11. 85% dark matter 13% hot gas 2% stars
Clusters contain large amounts of X-ray emitting hot gas
Temperature of hot gas (particle motions) tells us cluster mass
The mass is much more than gas and galaxies

12. All methods of measuring cluster mass indicate similar amounts of dark matter

13. 1E – The Bullet Cluster
Direct observation of Dark Matter

14. Proof that Dark Matter Exists
1E – A collision of galaxy clusters
A cluster of galaxies consists of three components
1. Galaxies
2. Hot Gas
3. Dark Matter

15. What’s going on with 1E ?
TWO clusters of galaxies collide

16. The gas interacts, the dark matter and galaxies don’t
The galaxies and dark matter pass through unimpeded, but the hot gas is separated from the clusters

17. Animation of 1E
link to animation:

18. Dark Matter The universe contains additional matter we cannot see
Dark matter interacts with normal matter through gravity
Dark matter does NOT interact with light the way the normal matter does
The Universe contains 5 or 6 times MORE dark matter than normal matter
All galaxies are embedded in clouds of dark matter
We do not know what it is!

19. What is DARK MATTER? Can’t see it, taste it, touch it, smell it…
We can only detect it by gravity
We don’t know!
Detecting Dark Matter is one of the most active areas of high energy physics, and a reason to build large accelerators.

20. Why is DARK MATTER important?
The formation of structure and of galaxies requires the extra mass provided by dark matter.
Without dark matter, the Universe would not exist as we know it

21. Final News Quiz on Tuesday! Project Due Nov 30
Happy Thanksgiving!
Unit 81, 82, 83
Final News Quiz on Tuesday!
Project Due Nov 30