How are light and heavy elements formed?
For an independent study course at my high school, I am researching the formation of the elements, both light and heavy. I have some basic understanding of how this is done, and I have also found some technical information that at this time I don't understand. Can you point me to some good articles on the topic, or perhaps cover some more advanced materials yourself?
The lightest elements (hydrogen, helium, deuterium, lithium) were produced in the Big Bang nucleosynthesis. According to the Big Bang theory, the temperatures in the early universe were so high that fusion reactions could take place. This resulted in the formation of light elements: hydrogen, deuterium, helium (two isotopes), lithium and trace amounts of beryllium.
Nuclear fusion in stars converts hydrogen into helium in all stars. In stars less massive than the Sun, this is the only reaction that takes place. In stars more massive than the Sun (but less massive than about 8 solar masses), further reactions that convert helium to carbon and oxygen take place in succesive stages of stellar evolution. In the very massive stars, the reaction chain continues to produce elements like silicon upto iron.
Elements higher than iron cannot be formed through fusion as one has to supply energy for the reaction to take place. However, we do see elements higher than iron around us. So how did these elements form? The answer is supernovae. In a supernova explosion, neutron capture reactions take place (this is not fusion), leading to the formation of heavy elements. This is the reason why it is said that most of the stuff that we see around us come from stars and supernovae (the heavy elements part). If you go into technical details, then there are two processes of neutron capture called rapid process (r-process) and the slow process (s-process), and these lead to formation of different elements.
For more details, refer the following websites:
2. Fusion in stars like the Sun
Related questions:
- How are elements heavier than iron formed?
- Why will fusion wait until hydrogen is gone before starting to fuse heavier atoms?
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