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The Question

(Submitted February 02, 1998)

I'm in 8th grade in a Science class and my question is what is a supernova and how does it affect us?

The Answer

A supernova is an explosion at the very end of the life of certain types of stars. You can find more information about supernovae at

in the section about massive stars.

There is much more information also included in our Imagine the Universe! web site you can find by going to:

and click on the search button and asking it to search for "supernova".

These pages explain what a supernova is, how they happen, and the different kinds of supernovae. These will answer your question about what a supernova is.

Your other question was about how supernovae affect us. They can affect us in some important ways. First and foremost, we and much of the Earth are made of the material supernovae created. According to current theories about the formation of the Universe, all of the original material in the Universe was hydrogen and helium, with very slight traces of some other materials. All the stuff we, and the Earth around us, are made of, like iron and oxygen and carbon, has come from that initial material being fused to form heavier elements in the cores of stars. But the heaviest elements, like iron, are only formed in the massive stars which end their lives in supernovae. Our blood has iron in the hemoglobin which is vital to our ability to breath. So without supernovae, most forms of life on Earth, including us, would not be possible. And much of the material the Earth is made of would not exist.

Supernovae also create shock waves through the interstellar medium (the stuff between stars), compressing material there. Astronomers believe that these shock waves are vital to the process of star formation, causing large clouds of gas to collapse and form new stars. No supernovae, no new stars.

Supernovae throw much of the material from their parent star back out into the interstellar medium, changing its chemical composition. This adds many elements to the interstellar medium which were not present before, or were only present in trace amounts. Other less massive stars also enrich the interstellar medium, but lack many of the heavier elements. The gradual enrichment of the interstellar medium with heavier elements has made subtle changes to how stars burn: the fusion process in our own Sun is moderated by the presence of carbon. The first stars in the Universe had much less carbon and their lives were somewhat different from modern stars. Stars which will be formed in the future will have even more of these heavier elements and will have somewhat different life cycles. So supernovae play a very important part in this chemical evolution of the Universe.

Jesse Allen
for Ask an Astrophysicist

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