Chapter 16 and 17: Discovering Galaxies

The Milky Way Galaxy

Whenever life gets you down, Mrs. Brown,And things seem hard or tough,And people are stupid, obnoxious or daft,And you feel that you've had quite eno-o-o-o-o-ough...Just remember that you're standing on a planet that's evolvingAnd revolving at nine hundred miles an hour,That's orbiting at nineteen miles a second, so it's reckoned,A sun that is the source of all our power.The sun and you and me and all the stars that we can seeAre moving at a million miles a dayIn an outer spiral arm, at forty thousand miles an hour,Of the galaxy we call the "Milky Way".Our galaxy itself contains a hundred billion stars.It's a hundred thousand light years side to side.It bulges in the middle, sixteen thousand light years thick,But out by us, it's just three thousand light years wide.We're thirty thousand light years from galactic central point.We go 'round every two hundred million years,And our galaxy is only one of millions of billionsIn this amazing and expanding universe.

Galaxies seem to take one of four different appearances

SPIRALS

Galaxies seem to take one of four different appearances

BARRED SPIRALS

Edge on Spiral

Galaxies seem to take one of four different appearances

ELLIPTICALS

Type E0 Type E3 Type E6

Galaxies seem to take one of four different appearances

IRREGULAR

Galaxies that look like merger remnants

Galaxy Mergers

Mergers cause the shapes of galaxies to change over time.

E

CD

B

Galaxy Classification

A

F

Our View of the Milky Way Galaxy

Our Milky Way Galaxy?

90% of a Galaxy is Dark Matter!

Measuring the amount of Dark Matter in the Universe: Gravitational Lensing

Einstein’s General Theory of Relativity says that light from a distant object gets bent when it passes through a gravitational field of an intervening object.

Perfectly Aligned Slightly Misaligned

Gravitational lensing

Gravitational Lensing:Evidence for dark matter

The Birth and Life of GalaxiesView of the Early Universe with WMAP (2003)

Early Universe showed slight variations in density!

Are the density variations the seeds of galaxy formation??

Now the popular choice for galaxy formation!

Young Galaxies

• smaller

• bluer

• more irregular

• higher starforming rates

Galaxies as they appeared more than 10 billion years ago.

Galaxies are Grouped in Clusters

Now the popular choice for galaxy formation!

The Local Group

The Local Super Cluster

Large-Scale Structure in the Universe

Superclusters, walls,and voids dominate thelarge scale structureof the Universe