galaxies

elliptical galaxies

Figure 26.10 shows a typical elliptical galaxy. Elliptical galaxies are oval in shape. The smallest are called dwarf elliptical galaxies. Look back at the image of the Andromeda Galaxy. It has two dwarf elliptical galaxies as its companions. Dwarf galaxies are often found near larger galaxies. They sometimes collide with and merge into their larger neighbors. Giant elliptical galaxies contain over a trillion stars. Elliptical galaxies are red to yellow in color because they contain mostly old stars. Most contain very little gas and dust because the material has already formed into stars.

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spiral galaxies

Galaxies are divided into three types, according to shape. There are spiral galaxies, elliptical galaxies, and irregular galaxies. Spiral galaxies are a rotating disk of stars and dust. In the center is a dense bulge of material. Several arms spiral out from the center. Spiral galaxies have lots of gas and dust and many young stars. Figure 26.9 shows a spiral galaxy from the side. You can see the disk and central bulge.

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shape and size

The Milky Way Galaxy is a spiral galaxy that contains about 400 billion stars. Like other spiral galaxies, it has a disk, a central bulge, and spiral arms. The disk is about 100,000 light-years across. It is about 3,000 light years thick. Most of the galaxys gas, dust, young stars, and open clusters are in the disk. Some astronomers think that there is a gigantic black hole at the center of the galaxy. Figure 26.13 shows what the Milky Way probably looks like from the outside. Our solar system is within one of the spiral arms. Most of the stars we see in the sky are relatively nearby stars that are also in this spiral arm. We are a little more than halfway out from the center of the Galaxy to the edge, as shown in Figure 26.13. Our solar system orbits the center of the galaxy as the galaxy spins. One orbit of the solar system takes about 225 to 250 million years. The solar system has orbited 20 to 25 times since it formed 4.6 billion years ago.

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irregular galaxies

Look at the galaxy in Figure 26.11. Do you think this is a spiral galaxy or an elliptical galaxy? It doesnt look like either! If a galaxy is not spiral or elliptical, it is an irregular galaxy. Most irregular galaxies have been deformed. This can occur either by the pull of a larger galaxy or by a collision with another galaxy.

the milky way galaxy

If you get away from city lights and look up in the sky on a very clear night, you will see something spectacular. A band of milky light stretches across the sky, as in Figure 26.12. This band is the disk of the Milky Way Galaxy. This is the galaxy where we all live. The Milky Way Galaxy looks different to us than other galaxies because our view is from inside of it!

types of galaxies

The biggest groups of stars are called galaxies. A few million to many billions of stars may make up a galaxy. With the unaided eye, every star you can see is part of the Milky Way Galaxy. All the other galaxies are extremely far away. The closest spiral galaxy, the Andromeda Galaxy, shown in Figure 26.8, is 2,500,000 light years away and contains one trillion stars!

star clusters

Star clusters are groups of stars smaller than a galaxy. There are two main types, open clusters and globular clusters. Open clusters are groups of up to a few thousand stars held together by gravity. The Jewel Box, shown in Figure an open cluster are young stars that all formed from the same nebula. Globular clusters are groups of tens to hundreds of thousands of stars held tightly together by gravity. Globular clusters have a definite, spherical shape. They contain mostly old, reddish stars. Near the center of a globular cluster, the stars are closer together. Figure 26.7 shows a globular cluster. The heart of the globular cluster M13 has hundreds of thousands of stars. M13 is 145 light years in diameter. The cluster contains red and blue giant stars.

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instructional diagrams

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questions

Types of star clusters include

-->  a. open clusters.

b. spiral clusters.

c. elliptical clusters.

d. all of the above

A galaxy can contain how many stars?

a. up to 500

b. up to 30,000

c. up to 10 million

-->  d. up to many billions

Elliptical galaxies contain

a. a lot of gas and dust.

b. mainly young stars.

-->  c. mostly red or yellow stars.

d. two of the above

How are irregular galaxies deformed?

-->  a. from collisions with other galaxies

b. from gravitational pull from a black hole

c. from extremely rapid spin

d. from extremely rapid formation

Types of galaxies include

-->  a. spiral galaxies.

b. cluster galaxies.

c. circular galaxies.

d. globular galaxies.

Most elliptical galaxies have very little gas and dust because

a. they are very young

-->  b. the dust and gas have already formed stars

c. the dust and gas is pulled into supermassive black holes at the center

d. none of these

Spiral galaxies have

a. only old stars

b. fewer stars than globular clusters

-->  c. a bulge at the center

d. an elliptical shape

The stars in an open cluster are mostly

a. old stars.

-->  b. young stars.

c. reddish stars.

d. two of the above

Galaxies that do not have a clearly defined shape are called

a. deformed galaxies.

-->  b. irregular galaxies.

c. dwarf galaxies.

d. open galaxies.

Globular clusters

a. have a lot of dust in them

b. contain a few hundred to a few thousand stars

-->  c. contain mostly reddish stars

d. all of these

Scientists estimate that the Milky Way Galaxy contains about

a. 40,000 stars.

b. 400,000 stars.

c. 40 million stars.

-->  d. 400 billion stars.

Some astronomers think that at the center of our galaxy there is a

a. neutron star.

b. supernova.

c. red supergiant.

-->  d. black hole.

type of galaxy that is a rotating disk of stars and dust

a. elliptical galaxy

b. globular cluster

c. irregular galaxy

d. open cluster

-->  e. spiral galaxy

f. star cluster

g. galaxy

star cluster containing up to a few thousand stars

a. elliptical galaxy

b. globular cluster

c. irregular galaxy

-->  d. open cluster

e. spiral galaxy

f. star cluster

g. galaxy

type of galaxy that is oval in shape

-->  a. elliptical galaxy

b. globular cluster

c. irregular galaxy

d. open cluster

e. spiral galaxy

f. star cluster

g. galaxy

The Milky Way appears as a band of light across the night sky.

-->  a. true

b. false

group of stars that is smaller than a galaxy

a. elliptical galaxy

b. globular cluster

c. irregular galaxy

d. open cluster

e. spiral galaxy

-->  f. star cluster

g. galaxy

Most of the galaxies we see from Earth are dwarf galaxies.

a. true

-->  b. false

very large group of stars that are held together by gravity

a. elliptical galaxy

b. globular cluster

c. irregular galaxy

d. open cluster

e. spiral galaxy

f. star cluster

-->  g. galaxy

star cluster containing up to tens of thousands of stars

a. elliptical galaxy

-->  b. globular cluster

c. irregular galaxy

d. open cluster

e. spiral galaxy

f. star cluster

g. galaxy

Elliptical galaxies have mostly younger blue stars.

a. true

-->  b. false

type of galaxy that is neither spiral nor elliptical in shape

a. elliptical galaxy

b. globular cluster

-->  c. irregular galaxy

d. open cluster

e. spiral galaxy

f. star cluster

g. galaxy

Every star that you see without a telescope is in the Milky Way Galaxy.

-->  a. true

b. false

Our solar system is slowly spinning around our galaxy.

-->  a. true

b. false

There are billions of galaxies in the universe.

-->  a. true

b. false

A star cluster may contain one or more galaxies.

a. true

-->  b. false

Open star clusters contain more stars than globular star clusters.

a. true

-->  b. false

Galaxies are divided into types based on size.

a. true

-->  b. false

Spiral galaxies are generally older than elliptical galaxies.

a. true

-->  b. false

Dwarf galaxies are often found near larger galaxies.

-->  a. true

b. false

Some galaxies contain over a trillion stars.

-->  a. true

b. false

Our solar system is within one of the spiral arms of our galaxy.

-->  a. true

b. false

Our solar system orbits the central disk of our galaxy.

-->  a. true

b. false

From Earth, our galaxy looks like a giant spiral.

a. true

-->  b. false

diagram questions

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