1. THE MILKY WAY
Intro Info

2. galaxies, and each galaxy has on the average
The Universe has about
100 billion to 1 trillion
galaxies, and each galaxy has on the average
100 billion and 1 trillion numbers of stars .

3. So how many stars are there roughly???
Minimum Average: x 1011
Maximum Average: x 1012
BETWEEN 1022 AND 1024 STARS!!!
10 sextillion and 1 septillion STARS!

4. Dwarf Galaxies
About 10 million stars

5. Irregular Galaxies
Can have up to 10 trillion stars

6. The Milky Way Barred spiral galaxy Over 200 billion stars
One of tens of billions of galaxies in the observable universe

7. The Milky Way is about 100 000 light-years across, about 10 000 light-years thick.
Our Solar System is located near the edge of one of the arms. It is located about light-years from the middle.

8. Size and Shape
Clouds of interstellar medium (dust and gas) fill the galactic disk and prevent our ability to see through it.
This long fooled astronomers to think we lived near the centre of our galaxy
In the 1920s, Harlow Shapley found that the globular clusters orbit a point tens of thousands of light years from our Sun.
This point is the centre of our galaxy, not our Sun!!
Also not the centre of our Universe!!!

9. Size and Shape
Radio and infrared technologies allow us to see through the interstellar dust.
Our Sun lies about light-years from the centre of the Milky Way

10. Size and Shape Flat disk of stars with a bright central bulge (bar)
Spiral arms
Dimmer round halo surrounding everything
A few hundred globular clusters of stars orbit the galaxy’s centre
In 2005, the Spitzer Space Telescope collected evidence that the Milky Way is a Barred Spiral

20. Terms Gas Halo: also called galactic halo
A gas halo is a ring of gas and stars surrounding a galaxy.
A globular cluster is a spherical collection of stars that orbits a galaxy core as a satellite. They are older stars.

21. What is in the middle?
Reading available at that web address
Reading available at that web address

22. The Milky Way
Has satellite galaxies (it is very large)

23. The Local Group The Milky Way is part of the Local Group.
The Milky Way and Andromeda are the two most massive galaxies in this group (both spiral galaxies).
Composed of 30 galaxies with the gravitational centre between the Milky Way and Andromeda.
10 million light years in diameter.

25. Virgo Cluster
The Milky Way is part of the Local Group which is part of the Virgo Cluster.
1300 galaxies in this group.
Many members of this galaxy are visible with a telescope.
It is located in the constellation Virgo.

26. Virgo Supercluster (Local Supercluster)
An irregular supercluster of galaxies that contains the Milky Way, Local Group and Virgo Cluster.
Contains 100 galaxy groups and clusters
Diameter of 110 million light years

28. Comparison of Solar System to Virgo Supercluster

29. We can see the same distance in all directions.
It appears that we are in the middle of the Universe. That isn’t true. We are only in the middle of what we can
see.
We can see the same distance in all directions.

30. The next closest galaxy to us is Andromeda and is about
2 million light years away.

31. In 1842, Christian Doppler explained why an object making a noise sounds more shrill when it is coming towards you, and sounds deeper when it is going away from you. When an object is coming towards you, the sound vibrations in the air are travelling in the same direction as the object.

32. When the object passes you and moves away, the sound vibrations are travelling in the opposite direction from the moving object.
Every star sends out light waves. The light appears bluer if the star is coming towards us, and redder if it is moving away.

33. In the 1930’s, astronomers found that most galaxies show a red shift
In the 1930’s, astronomers found that most galaxies show a red shift. This means that they are moving away from our galaxy. The farthest galaxies are moving away at thousands of kilometres a minute!

34. In the 1950s, astronomers discovered that some galaxies sent out radio waves. Their light was very strange because the light waves were stretched out. These galaxies were called
quasars
and they have the largest red shifts known. They are the farthest from us. Looking at quasars is like looking into the past.

35. The farthest known quasar is about 12 billion light-years away.
When we look out into space, out beyond the quasars, we are really looking back into
time.
Why are all galaxies moving away from us? Why should the galaxies farthest away from us move away the fastest? What’s so special about us?

36. Quasars
A very energetic and distant ACTIVE galaxy. They are the most luminous objects in the universe.
QUASAR: quasi-stellar radio source
Quasars were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than extended sources similar to galaxies.

37. Rotation of Galaxies – The Missing Mass Problem
Doppler Effect used to measure the speed of material orbiting around the center of a galaxy.
Photographs of galaxies show that luminous material appears to be concentrated towards the center and drops off with increasing distance.
Distance from galaxy center
Orbital speed
Observed
Expected 37

38. Rotation of Galaxies – The Missing Mass Problem
If matter were really concentrated in this fashion, we would see “rotation curves” following the “expected” path in the diagram at right.
What is observed instead is that rotation curves tend to remain high as far out as they can be measured. This means the existence of massive halos of dark matter in galaxies. The nature of the material comprising this dark matter is completely unknown at present, making this one of the greatest problems of contemporary astronomy.
Distance from galaxy center
Orbital speed
Observed
Expected 38

39. Gravitational Lensing in Abell 2218 Cluster
As predicted by Einstein’s General Theory of Relativity, a compact intervening object is bending and distorting light from individual members of this cluster so that we see a halo effect.
Hubble Space Telescope Image 39

40. A Lensed Quasar
An intervening galaxy between us and this distant quasar is causing light from the quasar to be bent along curved paths that give rise to an Einstein cross, a phenomenon predicted by Einstein’s General Theory of Relativity.
National Optical Astronomy Observatories Image 40