Objectives: 1) To learn about Spirals 2) To learn about Barred Spirals

1. Goal: To know the different types of galaxies and to understand their differences and similarities. • Objectives: • 1) To learn about Spirals • 2) To learn about Barred Spirals • 3) To learn about Elliptical Galaxies • 4) To learn about Irregular Galaxies

2. What type of galaxy is this?

3. Andromeda is a spiral galaxy.

4. What kind of galaxy do we live in? • a) Spiral galaxy • b) Irregular galaxy • c) Elliptical galaxy • d) Barred Spiral galaxy

5. (M110) What kind of galaxy? • a) Spiral • b) Irregular • c) Elliptical • d) Barred Spiral

6. Large Magellanic Clouds • What kind of galaxy? • a) Spiral • b) Irregular • c) Elliptical • d) Barred Spiral

7. Spiral Galaxies • Spiral Galaxies have 3 components: • Disk • Bulge (the center) • Halo • Spiral Galaxies have density waves in their discs which cause star formation. • Star formation regions are the brightest region for a galaxy, so that is the part we usually see.

8. Spiral Galaxies cont • Spiral Galaxies usually have about a trillion solar masses and 100-400 billion stars (give or take a factor of 10). • They are usually about the size of our galaxy (give or take a factor of 10). • Because of this you can somewhat tell the distance to a spiral galaxy based on its image size (further away appears smaller).

9. Viewing Spiral Galaxies - inclination • The angle the disk makes with us changes what we see! • (top is M51 the Whirlpool galaxy)

10. Supernova!

11. Elliptical Galaxies • Elliptical galaxies are egg shaped. • Stars orbit around the center of the galaxy HOWEVER each star has its own orbit. • There is no orbital plane like in spirals. (M87) Center of Virgo cluster 50 million light years D > 1 million light years

12. Ellipticals cont. • The smallest AND the biggest galaxies are elliptical galaxies! • In the centers of clusters you tend to find Giant Elliptical Galaxies that can be 10-100 times more massive than our galaxy. • Spirals tend to hang on their own – but often have small satellite galaxies. • The smallest galaxies are dwarf ellipticals. • Elliptical galaxies don’t have much dust or gas so new stars don’t form. • So, they just have the old stars.

13. Jet! • M87 probably has a massive black hole in its center (billions of solar masses). • 6500 light years long

14. Most though • Most of the galaxies in our universe are probably Dwarf Elliptical galaxies. • However these galaxies are so dim (with only a few million stars and no dust you can literally see through these galaxies) that they are hard to find at any decent distance. • So, we can’t find them all.

15. Irregular Galaxies • Are commonly found orbiting bigger galaxies. • Big galaxies eat the smaller ones. • These are the ones being slowly torn apart before the bigger galaxy digests them. • Yes, galaxies do interact with one another! • The result:

17. Irregular galaxies look like: • They are very distorted. • Often they have large star forming regions. • Last page, blue was Small Magellanic Clouds. The yellow regions were both globular clusters (NGC 362 top left and the larger one is the nearer to us 47 Tucanae – still 13000 light years away).

19. So, we know everything there is to know right? Lets find out What kind of galaxy is this? • Spiral • Elliptical • Irregular Why does it look like this?

20. COLLISIONS! • Weird things happen when galaxies collide (however stars don’t collide – the distances between stars is way too big). • There are a few possibilities.

21. Case 1: small galaxy collides with big one • In this case the small galaxy is ripped apart tidally. • In the short term it may orbit the galaxy a few times in a highly warped state (and be an irregular galaxy). • No matter what, it will eventually be merged into the larger galaxy. • There may be some star formation in the big galaxy as this will set out a density wave, but most of the star formation will occur in the small galaxy – if it has any gas in it.

22. Case 2: equal sized galaxies collide • If equal sized galaxies collide a whole multitude of possible results can occur. • If they collide at a very high velocity the gasses will collide and heat up a lot. • This heated gas will escape from the galaxy – which means an end to star formation in the galaxy.

23. Case 2 usual result • The usual result is that the 2 galaxies merge together. • The tidal forces of the merge mix up the galaxies randomly. • While it may spark a period of star formation the end galaxy is a giant elliptical galaxy. • Sometimes tidal tails are also created.

24. Another effect • Since you add a lot of gas which ends up being accreted by the center of the galaxy (where the black holes lie) you tend to get active galaxies. • These are galaxies that often times have long jets and are very bright (star formation + bright accretion disk in the nucleus).

25. Conclusion • There are 3 main types of galaxies although some have sub groups. • Orientation affects our view of galaxies. • Galaxies interact creating interesting images! • Big galaxies eat the small galaxies.