How Stars are Born

When we look up at the night sky, we rarely think about the technical aspects of the formation of our universe. We see stars, and sometimes planets and comets, and just think that they are simply beautiful. However, when we do learn about how stars, or planets or comets, are made, we can also find them even more awe-inspiring than ever before.

Stars are formed in cold, dark nebulae. In our own galaxy, the Milky Way, stars are formed in the spiral arms. If you look up at the night sky in a place that is not polluted with light, we can see the disk of the Milky Way. This disk is made up of interstellar dust and gas which create new stars.

These cold, dark nebulae are found mainly in the spiral arms of our galaxy, but more so in giant molecular clouds. Because dark nebulae are not easily found (they are “dark,” therefore they do not emit any light), we have to use radio telescopes to find them. Areas with intense CO emission that show up in images using radio telescopes tell us where these dark nebulae are. Philip Solomon and Nicholas Scoville were American astronomers who first used CO radiation to find dark nebulae. When they found those dark nebulae in the Milky Way, they discovered that they were concentrated along the galaxy’s spiral arms.

Supernovae can also put out interstellar dust and help create new stars. You might think that supernovae means that the dead stars are long gone and whatever they were made of simply go away or disappear. But this isn’t the case. Supernova remnants are bright, colorful figures in the night sky. When a supernova explodes, it warms up the interstellar dust and gases that surround it. The shockwave of a supernova excites the surrounding hydrogen gas (contained in what is called a giant molecular cloud) and forms new stars.

One good example of a place in the night sky where star birth and formation are occuring is in the Canis Major R1 association. The Canis Major R1 Assocation looks bright red, but this isn’t because the stars there are old. Actually, shockwaves from supernovae are exciting the surrounding gas, making the whole thing appear bright red.

Other processes can help jumpstart the birth of stars. For instance, when two interstellar clouds collide, compression can occur and new stars are formed. Stellar winds from O and B stars can put pressure on interstellar clouds so that compression can also occur. Astronomers are still learning much more about star formation, so other instances and observations may emerge in coming years.


Freedman, Roger A. “Universe.” Chapter 18. New York: W. H. Freeman & Company, 2008.