GalaxiesGalaxies

NGC4013, a large, nearby, edge-on spiral galaxy. Taken at the WIYN

Telescope

GalaxiesGalaxies UniverseUniverse- all of space and everything in it- all of space and everything in it

More than 100 billion galaxiesMore than 100 billion galaxies

GalaxyGalaxy- giant structure that contains - giant structure that contains hundreds of billions of starshundreds of billions of stars, dust, and gas , dust, and gas held together by gravity held together by gravity

Classified into three categories by Classified into three categories by shape shape

GalaxiesGalaxies

Galaxies range in diameter from a few Galaxies range in diameter from a few thousand to a half-million light-years. thousand to a half-million light-years.

Small galaxies have fewer than a billion Small galaxies have fewer than a billion stars. stars.

Large galaxies have more than a trillion. Large galaxies have more than a trillion.

1. Spiral Galaxies1. Spiral Galaxies

Looks like a pinwheelLooks like a pinwheel

Most galaxies are spiralMost galaxies are spiral

Stars are formingStars are forming

Has a center of bright Has a center of bright

starsstars

Has 2 or more Has 2 or more

spiral armsspiral armsLargestLargest

•

Milky way GalaxyMilky way Galaxy

Our sun is 25,000 Our sun is 25,000 light years from the light years from the center of the center of the galaxygalaxy

Can’t see the Can’t see the center because it is center because it is hidden by huge hidden by huge clouds of stars, clouds of stars, gas, and dustgas, and dust

Sagittarius and the Central Milky Way

Milky wayMilky way

2.Elliptical Galaxies2.Elliptical Galaxies

Look like flattened ballsLook like flattened balls

Billions of starsBillions of stars

Little gas and dust Little gas and dust between starsbetween stars

No new stars formingNo new stars forming

Only old starsOnly old stars

Smaller than Smaller than spiral galaxiesspiral galaxies

elliptical

3. Irregular Galaxies3. Irregular Galaxies

Fewer starsFewer stars

No definite shapeNo definite shape

Smallest galaxiesSmallest galaxies

Least common galaxiesLeast common galaxies

Leo A: Nearby Dwarf Irregular Galaxy

QuasarQuasar

An enormously bright, distant galaxy with a An enormously bright, distant galaxy with a giant black hole at its center.giant black hole at its center.

Identify the shape of each galaxy.Identify the shape of each galaxy.

Elliptical

Spiral

about 350 million light-years from Earth. Cataloged as AM0500-620, the pair is located in the southern constellation Dorado

Only three galaxies outside the Milky Way Only three galaxies outside the Milky Way are visible with the unaided eye. are visible with the unaided eye.

People in the Northern Hemisphere can People in the Northern Hemisphere can see the Andromeda Galaxy, which is about see the Andromeda Galaxy, which is about 2 million light-years away. 2 million light-years away.

People in the Southern Hemisphere can People in the Southern Hemisphere can see the Large Magellanic Cloud, which is see the Large Magellanic Cloud, which is about 160,000 light-years from Earth, and about 160,000 light-years from Earth, and the Small Magellanic Cloud, which is about the Small Magellanic Cloud, which is about 180,000 light-years away. 180,000 light-years away.

Visible GalaxiesVisible Galaxies

Andromeda GalaxyAndromeda Galaxy

Large Magellanic CloudLarge Magellanic Cloud

Small Magellanic Cloud

All big bang theories of galaxy All big bang theories of galaxy formation agree that no new galaxies formation agree that no new galaxies -- or very few -- have formed since -- or very few -- have formed since the earliest times. the earliest times.

Local GroupLocal Group

Small galaxy cluster- 30 galaxiesSmall galaxy cluster- 30 galaxies

Caused by gravityCaused by gravity

Most galaxies are orbiting the Milky Way or Most galaxies are orbiting the Milky Way or Andromeda galaxiesAndromeda galaxies

3 million light years across3 million light years across

Mostly spiral galaxiesMostly spiral galaxies

Virgo SuperclusterVirgo Supercluster

Local Group, Virgo ClusterLocal Group, Virgo Cluster

Caused by gravityCaused by gravity

200 million light years across200 million light years across