1. January 2nd 2013
Objective
Warm-Up
Students will know how galaxies are classified in order to identify the various types
What is the name of the galaxy that contains the sun, the earth and the known planets?
What is bigger: the solar system or a galaxy?
What is the name of our galaxy?

2. What is a Galaxy?
A dense group of stars, dark matter, dust and gas held together by gravity.
Dark matter- matter that produces no detectable light or other form of energy, but can be detected through its gravitational pull on visible stars and gas.

3. Galaxies:
Small galaxies
Contain only about a million stars
Dust and gas
Milky Way galaxy
Contains several hundred billion stars
Dark Matter -90% of the total mass of the galaxy
Large galaxies
Contain more than one trillion stars
At the center (heart) of most galaxies there is a supermassive black hole

4. Formation of Galaxies Theory 1: Theory 2:
Galaxies were formed when vast clouds of dust and gas collapsed under their own gravitational pull, allowing stars to form
Theory 2:
The young universe contained many small “lumps” of matter which clumped together to form galaxies.
Hubble space telescope has gathered images to support this theory
Most of the early galaxies were spirals but over time many spirals merged to form elliptical

5. Galaxies
They are still being formed!

6. Galaxy Mergers
Larger galaxies consume smaller galaxies. Most bright galaxies are formed from the merger of two or more smaller galaxies.
Galaxies are very massive which means they also have a strong gravitational pull.
This force can cause galaxies to attach themselves to one another and merge over time
Few hundred million to a few billion years to complete

7. Results of Galaxy Mergers
When two or more large spiral galaxies merge they form elliptical galaxies containing more than a trillion stars.
Trigger intense bursts of new star formation
Create gigantic black holes
Galaxy Collision

8. Types of Galaxies: Shape Classification
Spiral Galaxy
Most beautiful type of galaxy
Examples: Milky way, Andromeda(M31)
Flat disks of stars with bright bulges at the center
Spiral arms wrap around the bulge
Arms are a result of density waves which influence matter as they pass.
Color of the spiral arms depend on the new born stars and their characteristics.
Dark spaces between the arms contain older stars, which are not as bright

9. Types of Galaxies: Shape Classification
Spiral Barred Galaxies
Stars in the center form a bar
The arms of the spiral shoot out from the end of the bar
The Milky Way galaxy is a spiral bar galaxy

10. Types of Galaxies: Shape Classification
Elliptical
Look like fat, fuzzy footballs
Stars wrap completely around the galaxy’s heart in all directions
Largest galaxies in the universe are elliptical in shape
Contain more than a trillion stars
Span more than one million light years

11. Types of Galaxies: Shape Classification
Irregular Galaxies
This category has a mixture of shapes- anything that is not a spiral or elliptical
No identifiable form
Usually the smallest galaxies are irregular in shape
Contain about one million stars
Irregular galaxies are hypothesized to be the building blocks that came together to form the first larger galaxies

12. Types of Galaxies: Energy Classification
Active Galaxies
Observing these galaxies in the X- ray, ultraviolet, infrared and radio wavelengths, they appear to be giving off enormous amounts of energy
4 Classifications of Active galaxies
Seyfert galaxies
Have broad spectra indicating cores of hot, low-density ionized gas.
Radio galaxies
Nuclei emit jets of high-velocity gas above and below the galaxy -- the jets interact with magnetic fields and emit radio signals.
Quasars
Most energetic objects in the universe.
Blazars
 Jet emanating from the galaxy.

13. Types of Galaxies: Energy Classification
Normal Galaxies
most of the light comes from the stars in visible wavelengths and is evenly distributed throughout the galaxy

14. Closure What is the most common way for classifying galaxies?
Classify one of the galaxies from the activity. Explain why it is classified that way.

15. Objective: You will use the different types of galaxies and their characteristics in order to explain the major systems within the universe and earth’s place in it.
Warm-Up: Classify the following galaxies by shape A B C

16. The Milky Way Galaxy
The Milky Way galaxy consists of a bulge of stars in the core, probably a thick bar of stars flanking the core, and bright spiral arms wrapping around the core.

17. The Milky Way Galaxy Size and structure of our galaxy Our solar system
Spiral galaxy
Thin flat disk
100,000 light-years in diameter
2,000 light years thick
Milky Way disk
The disk is surrounded by a halo of about 200 globular star clusters
Objects near the center of the galaxy move faster
Contains between 200 billion and 400 billion stars
A black hole (~ 4 million times more massive than our sun) at the center of the galaxy
Our solar system
27,000 light years from the center

18. The Local Group
The Milky Way Galaxy is part of a larger cosmic neighborhood- a collection of more than 35 galaxies known as the local group. These galaxies move through space as a single unit, bound by mutual gravitational pull.
Largest and heaviest members of the Local Group
Milky Way Galaxy
Large collection of satellite galaxies
Largest and best known satellite galaxies
Large and small Magellanic Clouds
200,000 light years away
Andromeda Galaxy (M31)
2.5 million light years away

19. In about 4 billion years
Astronomers predict that in several billion years, the Milky way galaxy and Andromeda will merge to form a galactic giant

20. Hubble’s Law
An observational effect of the expansion is that the farther a galaxy is from you, the faster it appears to be receding (Red shift in spectral line). This creates a relationship between the recessional velocity and distance. This phenomenon is known as Hubble's Law
Recessional Velocity = Hubble's Constant X Distance
V = Ho D
V is the observed velocity of the galaxy away from us, usually in km/sec
Ho is Hubble's Constant, in km/sec/Mpc (Ho = 73 km/sec/Mpc).
D is the distance to the galaxy in Mpc

21. Closure: Explain where Earth is located in the universe.
Be specific to include local group, location in the galaxy to the solar system.
When looking at the relationship between velocity and distance based on Hubble’s law, galaxies that are farther away are moving (faster or slower)?