1. Galaxies
Milky Way and Beyond

2. Galaxies
DAY 1: Types of Galaxies

3. Galaxy
A large system of stars held together by mutual gravitation and isolated from similar systems by vast regions of space

4. Classification Activity
Worksheets

6. Major Types
Spiral
Barred Spiral
Elliptical
Lenticular
Irregular

7. Spiral Central spherical “hub” Flattened disk of gas and dust
Hub consists of old red and yellow stars
Flattened disk of gas and dust
Stars occur throughout the disk
Young blue and white stars are found in the spiral arms
Space between the arms looks empty but is also full of stars
Spherical “halo” region above and below disk
The halo contains globular clusters and stray stars

8. Spiral Arms
The arms are rotating regions of star formation NOT rotating chains of stars
They consist of a “density wave”- a region that moves more slowly than the galaxy itself
The increased density helps to trigger the collapse of gas clouds and start star formation

9. SPIRAL EXAMPLE
ANDROMEDA GALAXY (Andromeda)

10. Barred Spiral
The majority of spiral galaxies have a straight bar on either side of the nucleus

11. BARRED SPIRAL EXAMPLE
SCULPTOR GALAXY (Sculptor)

12. Elliptical Ball shaped
Each star orbits the dense core in its own path not confined to any direction
Almost all stars are yellow and red
Rarely any star-forming gas and dust
Ellipticals are described according to their degree of elongation

13. Elliptical sizes
Elliptical galaxies span the range from the largest to smallest galaxies
Dwarf ellipticals are scattered in the space between larger galaxies
Giant ellipticals are found near the centre of galaxy clusters

14. ELLIPTICAL EXAMPLE
M87 (Virgo)

15. Lenticular Intermediate type of galaxy
Dominated by a roughly spherical nucleus
old red and yellow stars
Disk of stars and gas
No spiral arms
Little sign of star formation

16. LENTICULAR EXAMPLE
NGC 2787 (Ursa Major)

17. Irregular Galaxies that don’t fit other categories “Peculiars”=
Galaxies colliding with companions or being pulled apart by neighbour’s gravity.
“True Irregulars”=
Contain a lot of gas, dust and hot blue stars.
Great waves of star formation.
Frequently have vast, pink emission nebulae.

18. IRREGULAR EXAMPLE
CIGAR GALAXY (Ursa Major)