Normal Galaxies -Large gravitationally bound systems consisting of hundreds of billions of stars, enough gas and dust to make billions more stars, and dark matter.

The Milky Way -The Milky Way is our home galaxy - a vast rotating spiral of gas, dust, and hundreds of billions of stars. The Sun and its planetary system formed in the outer reaches of the Milky Way about 4.5 billion years ago.

Starburst Galaxies -Galaxies in which a violent event, such as near-collision, has caused a sudden, intense burst of star formation in the recent past. X-ray observations provide the best means for studying the formation and expansion of starburst winds.

Revised: October 11, 2012