Interstellar Matter

Our goal in this unit is to understand how stars form. To begin, let’s consider the “raw materials” that stars form out of - specifically, the interstellar medium. Read 20.1 The Interstellar Medium to learn about the composition and characteristics of the material between the stars.
The interstellar medium is defined as any material (mostly gas and just a little bit of dust) that is between the stars. That’s right, space is not entirely empty - there is approximately 1 atom of gas in every cubic centimeter of “empty” space! (For comparison, Earth’s atmosphere has about 10 million billion atoms in every cubic centimeter of air, so don’t get too excited.)
Sometimes, a region of the interstellar medium gathers together in an enormous cloud that we call a “nebula.” These objects are not only some of the most beautiful things found in the universe, but they also play an essential role in the formation of stars. Watch the video Light and Nebulas for an introduction to the different types of nebulae that astronomers observe in the sky.
Explore 20.2 Interstellar Gas to understand the properties of interstellar gas, including its temperature variations and molecular composition.
Review 20.3 Cosmic Dust to learn how interstellar dust affects the light from stars and its composition, including its rocky cores and icy mantles.
Our observations of nebulae and star-forming regions continue to improve with each new generation of space telescope. Check out the amazing video of the Carina Nebula from JWST, which begins with a wide view of the milky way in the night sky and then progressively zooms in to show a star-forming region inside the beautiful Carina Nebula.