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For as long as Man has walked the face of the Earth he has always looked to the stars and wondered about them. He made stories and legends and later on early theories to describe what they are and what are stars made of. It wouldn’t be until the first century A.D. that viable theories on what stars were and what they were made of would come about. It would not be until the late 1500s before astronomers would even begin to suspect that stars were similar to the sun. Currently through direct observations and new technologies we understand more about stars, their formation and their composition.
We now know that stars are mostly made of hydrogen. Hydrogen is the most plentiful element and gas in our universe and it is also the fuel that gives birth to stars and keeps them going for eons. Scientists theorize that the hydrogen found in the interstellar medium came from the Big Bang that dispersed matter and energy creating the universe. New Stars are formed in the denser parts of the interstellar medium as the forces of attraction and gravity start drawing them together.
Hydrogen is not the only element that makes up the composition of stars. Stars undergo the process of fusion to stay powered and this process fuses the hydrogen into denser elements as their life cycle progresses. The main fusion process fuses hydrogen into helium. As a star gets older store of hydrogen for nuclear fuel runs out. When it does the helium in the star is the next element to be used. When the core of a star starts turning into heavier elements like iron then it is near the end of its life cycle.
When a star reaches the end of its life cycle it will reach a critical mass and either collapse into a white dwarf or explode as a super nova. In either scenario a portion or most of all the gases used to make the star will be scattered again into a nebula and the process will start all over again. In the end we see that at some point in its life a star will be made up of or will develop a good portion of the elements that naturally occur in the periodic table.
We also know from average observation is that while all stars follow a general path of development, that the path of star formation is not necessarily the very same for every star. Some stars are richer in heavier elements while others have very little in their composition. A lot of it has to do with the nebula they were formed from. One interesting fact is that stars with more than average heavy metals in their make up are prime candidates for having planets.
We’ve done many episodes of Astronomy Cast about stars. Listen here, Episode 12: Where Do Baby Stars Come From?