4.2.1 The Age, Size, Shape, and Structure of the Milky Way

​The Age, Size, Shape, and Structure of the Milky Way
4.2.1

By Caitlin Ford

Objectives

- describe the size, shape, and structure of the Milky Way galaxy
- describe the parts of the Milky Way galaxy

The Milky Way: Your Galactic Home

Ancient people said the galaxy looked like a river of milk, so they named it Milky Way.

 

1610 - Galileo pointed his telescope at the Milky Way and saw thousands of stars.

 

100 billlion stars make up the Milky Way.

 

Some stars are in globular clusters - a large compact spherical star cluster that also contains gas and dust

Open Ended

Why can we see the Milky Way in our sky?

Formation and Structure

13.6 billion years ago

 

It started as a clump of gas with gravity, that pulled in nearby clumps and matter. It grew larger and larger. Stars were being produced at the same time, and gravity pulled everything together.

 

The galaxy has 4 spiral arms. It is 100,000 light years across.

 

Astronomers estimate the Miky Way is 1 trillion times the mass of the Sun.

Parts of the Milky Way

Nucleus - central region of the galaxy;  26,000 light years from Earth; 100 million stars are packed here, and a black hole lurks in the middle

Galactic Bulge - surrounds the nucleus; contains older stars

Galactic Disk - spiral arms are located here; contains younger stars

Galactic Halo - surrounds the disk and bulge; contains older stars

Dropdown

The Milky Way is a​

Select answer

galaxy.

Center of the Milky Way

The Nucleus - oldest area of the galaxy. Dense and compact. 

 

The Central Black Hole - discovered in 1974. Named Sagittarius A*. Supermassive; has a mass of 4 million times that of the Sun. One of the largest black holes known.

 

Accretion Disk - a band of material surrounding the black hole. Made of gas, dust, and debris attracted by gravity.

Galactic Bulge

Surrounds the nucleus.

 

10,000 light years across.

 

Oldest stars in the galaxy - between 10 and 13 billion years old

Galactic Disk

Thin, flat, circular structure that makes up most of the galaxy and formed as a result of collisions with other galaxies

 

100,000 light years across, thickness of 1000-2000 light years.

 

New stars form from clouds of gas and dust.

 

There are 4 spiral arms made of gas and stars

Galactic Halo

Halo - a spherical region of gas or stars surrounding a galaxy.

 

Inner Halo - closer to the galactic center. Higher density of stars.

 

Outer Halo - has fewer stars and is more spread out.

Hotspot

Where in the Milky Way can you find a supermassive black hole?

Collision?!

The Milky Way galaxy and Andromeda galaxy are on a collision course, expecting to merge in about 4.5 billion years.

 

Collisions between galaxies can produce dwarf galaxies - only containing a few billion stars and stay near bigger galaxies.

Multiple Choice

How far across is the Milky Way?

• 26,000 light years

• 2000 light years

• 1 billion light years

• 100,000 light years

Labeling

Label the Milky Way.

Drag labels to their correct position on the image

galactic halo

galactic disk

nucleus

Great job!

Today, you learned:

- about the structure, size, and shape of the Milky Way
- about different parts of the Milky Way galaxy