Galaxies

Galaxies

• A galaxy is a large group of stars, dust, and gases.

• They come in variable sizes and shapes.

• The largest have over a trillion stars.

Types

• In the 1920’s—Edwin Hubble began classifying galaxies-mostly by their shape.

• Spiral• Elliptical• Irregular

Spiral

Spiral galaxies bulge at the center and have arms that spiral. The arms are made of gases, dust, and new stars that formed in the denser regions.

The Milky Way is believed to be a spiral galaxy

Elliptical

• Cucumber shaped, very bright centers and very little dust and gas

• About 1/3 of all galaxies are classified as elliptical.

• Usually contain old stars.• Huge elliptical galaxies are called

Giant Elliptical • Smaller elliptical galaxies are called

dwarf galaxiesGiant Elliptical

Irregular

These are basically the galaxies that did not “fit” into the other categories.

They are often companions of Large Spiral Galaxies that could be the cause of their irregular shapes.

Content of Galaxies

• Billions of stars• gas clouds ( Nebulas) • planetary systems.

Nebula

• Clouds of gases• A. new stars are born• B. where stars explode when they

dieSpiral Galaxies usually contain Nebulas

Star Cluster

• Globular cluster-– group of stars that looks like a ball

and contains up to 1 million stars• Found in « halo » that can surround a spiral galaxy

Open Cluster

• Group of closely packed stars that are usually located along the spiral disk of a galaxy.

• Newly formed Open Clusters have bright Blue Stars

• Few stars range from 100’s –1000’s

Quasars

• Among the most distant objects in the space.

• They are starlight sources of light extremely far away.

• They are among the most powerful energy sources in the universe.