1. CHAPTER 31 THE GALAXIES & THE UNIVERSE

2. GALAXIES Scattered throughout the universe Made up of stars, dust and gas held together by gravity There are three main types of galaxies... Edwin Hubble (astronomer) classified galaxies according to their shape (1926)

3. GALAXY ANATOMY Some galaxies have high energy activity in their cores = active galactic nuclei

4. SPIRAL GALAXIES Barred spiral galaxies have an elongated central region Normal spiral galaxies do not have an elongated central region

5. ELLIPTICAL GALAXIES Lack the structure of a spiral galaxy Looks more like a simple elliptical shaped object Some can be more elongated than others Radio galaxies (often giant elliptical galaxies) emit as much or more energy in radio waves than they do visible light. Have unusual properties

6. IRREGULAR GALAXY Lacks any noticeable shape Varies from one to another

7. HUBBLE’S CLASSIFICATION OF GALAXIES E = Elliptical 0 = round elliptical 7= elongated elliptical S = Spiral SB = Spiral Barred A = tightly wound arms, bright nucleus B = somewhere between A and C C = loosely wound arms, dim nucleus S0 = flat disk with no spiral arms

8. WHERE ARE WE? The Milky Way Galaxy A spiral galaxy that formed billions of years ago

9. OTHER GALAXIES Most galaxies are located in groups Our Milky Way is in a group called the Local Group About 2 million ly Groups gathered together are called clusters and many clusters together are called super-clusters. Andromeda Galaxy

10. HUBBLE’S LAW Hubble determined that the universe was expanding by noticing redshift in the galaxies. v=Hd V = speed at which a galaxy is moving away (km/s) D = distance to the galaxy H = Hubble’s constant km/s/Mpc

11. THE ORIGINS OF THE UNIVERSE

12. COSMOLOGY Scientific study of the universe as a whole. The universe is… well, everything. The universe is continually growing!

13. ORIGIN OF THE UNIVERSE – BIG BANG! Common scientific theory: the universe existed as a concentrated single point, containing all known matter and energy. About 13.7 billion years ago this point began to expand and has stayed expanding ever since

14. STEADY-STATE THEORY Proposes the universe looks the same on large scales to all observers But if the universe is expanding, how is this possible? Theory proposes that new matter is created and added to the universe as it expands (always 3 galaxies in the box)

15. WHAT WE KNOW FOR SURE, THE UNIVERSE IS STILL EXPANDING...... Because we know galaxies and stars are moving away from us (red shift or blue shift?) The farther away from Earth a galaxy is, the faster it is moving The redshift in many galaxies is very large, which means that those galaxies are moving away very quickly and are far away.

16. COSMIC BACKGROUND RADIATION 1965, some scientists discovered a persistent background noise in their radio antenna Caused by weak radiation called cosmic background radiation Appeared to come from all directions Helps us map the universe!

17. WRITE OUT THE QUESTION AND ANSWER OR USE COMPLETE SENTENCES What is our current model for the origin of the universe and what does it state? What are the three types of galaxies? What type of galaxy is our solar system in and what is that galaxy called? What do we use to gather information about our universe? (hint: spectrum)