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

What type of galaxy is this?

Andromeda is a spiral galaxy.

What kind of galaxy do we live in?

• a) Spiral galaxy

• b) Irregular galaxy

• c) Elliptical galaxy

• d) Barred Spiral galaxy

(M110) What kind of galaxy?• a) Spiral

• b) Irregular

• c) Elliptical

• d) Barred

Spiral

Large Magellanic Clouds

• What kind of galaxy?

• a) Spiral

• b) Irregular

• c) Elliptical

• d) Barred

Spiral

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.

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).

Viewing Spiral Galaxies - inclination

• The angle the disk makes with us changes what we see!

• (top is M51 the Whirlpool galaxy)

Supernova!

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 cluster50 million light yearsD > 1 million light years

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.

Jet!

• M87 probably has a massive black hole in its center (billions of solar masses).

• 6500 light years long

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.

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:

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).

So, we know everything there is to know right?

Lets find out

What kindof galaxy is this?a) Spiralb) Ellipticalc) Irregular

Why does it look like this?

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.

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.

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.

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.

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).

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.