Galaxies

Galaxies

Milky Way Galaxy

• 200 billion stars

• 100,000 light years in diameter

• 2,000 light years thick

• Sun is about 30,000 light years from galaxy’s center

• Local Group: small cluster of 17 galaxies (our neighbors)

• Andromeda is 2,000,000 lights years away

The Milky Way Galaxyhttp://map.gsfc.nasa.gov/ContentMedia/dirbe123_2p6dec.jpg

Infrared Image of the Core of the Milky Way Galaxyhttp://en.wikipedia.org/wiki/Milky_Way

Types of Galaxies

• Spiral

• Elliptical

• Irregular

• Galaxies are millions of light years apart!

Spiral galaxies

• Central lens-shaped bulge with millions of stars

• Bright nucleus with millions of stars• 2 Spiral arms come out from opposite

sides of nucleus• Arms trail behind as galaxy rotates• Milky Way is a spiral; ¾ of galaxies are

spirals• Contain stars of various ages

Spiral Galaxy IC342http://www.noao.edu/image_gallery/html/im1032.html

Elliptical galaxies

• Range from spherical to lens-shaped

• No arms

• Most of the stars are close to center

• Little gas & dust clouds

• No young stars or ongoing star formation

• Contain old stars

M60 Elliptical Galaxyhttp://www.calvin.edu/academic/phys/observatory/images/Astr111.Spring2007/

Diaz.html

Irregular galaxies

• Small, faint, less common

• Stars spread unevenly

• Contain young, blue stars & old stars

• Abundant gas & dust; vigorous ongoing star formation

• Often found close to larger galaxies

Small Magellanic Cloud: a dwarf irregular satellite galaxy of the Milky

Way. http://www.astronomynotes.com/galaxy/s5.htm

Quasars

• Discovered 1961• Emit radio waves, IR, visible, X rays• Most luminous objects (like 20 trillion suns)• Larger & more massive than any known star• Radiate light and radio waves at high rates• May be whole galaxies in early stage of

development, but so distant that we can’t see the galaxy itself.

Quasars continued

• Most distant objects in the universe

• 30,000 known, but the number is increasing as we have better probes

Quasars in the act of colliding with their companion galaxies.

http://www.rdrop.com/users/green/school/quasars.htm

Link to Chandra Website image gallery

• http://chandra.harvard.edu/xray_sources/quasars.html

19.3

• Read: p. 596 – 599

• Questions: p. 599 #1-6

(Put your answers in your notebook)