Galaxies and Stars

The universe… …is space and everything in it. http://commons.wikimedia.org/wiki/File:2MASX_J00482185-2507365_by_HST.jpg …is space and everything in it.

Galaxies A galaxy is a cluster of stars, gas, and dust that are held together by gravity. There are three main types of galaxies: Irregular Elliptical Spiral http://starchild.gsfc.nasa.gov/docs/StarChild/universe_level1/galaxies.html

Types of Galaxies – Irregular… Some galaxies does not have regular shapes They contain young stars, dust, and gas. http://commons.wikimedia.org/wiki/File:I_Zwicky_18a.jpg

Types of Galaxies – Elliptical... Elliptical galaxies look like a ball that has been flattened. These galaxies contain billions of stars, but have little gas and dust between the stars. Contain only old stars. http://commons.wikimedia.org/wiki/File:I_Zwicky_18a.jpg

Types of Galaxies –Spiral… Spiral galaxies consist of a flat, rotating disk with stars, gas, and dust and a central concentration of stars, known as the bulge. Contains middle aged stars http://commons.wikimedia.org/wiki/File:2MASX_J00482185-2507365_by_HST.jpg

Types of Galaxies – Barred Spiral… The arms terminate at the ends Looks like Spiral Galaxies without arms extending out. Contain old and new stars http://www.nasa.gov/mission_pages/hubble/science/hstimg_ngc6217.html

Milky Way A giant spiral galaxy including our Sun The disk’s diameter is 100,000 light years Mass is 1,000 to 2,000 billion times the mass of the Sun The Sun lies a little more than 30,000 light years from the center Cannot actually count the number of stars in the galaxy, can estimate as roughly 100 billion

Andromeda Galaxy The other large galaxy in our cluster 2 million light years away More luminous than us Visible to the naked eye

What makes up galaxies? Nebulas – giant clouds of gas and dust where new stars can form. It is considered the star nursery. Stars and star clusters Black Holes – now believed to be the center of all spiral and elliptical galaxies

Star Clusters Globular clusters look like a ball of stars with 20,000 to 100,000 stars on average. Newly formed open clusters have many bright blue stars with a few hundred to a few thousand stars.

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