MadSci Network: Astronomy

Re: How did the first stars form without dust.

Date: Fri Jul 20 13:45:52 2001
Posted By: Angelle Tanner, Grad student, Astronomy, UCLA
Area of science: Astronomy
ID: 993315363.As

You have fallen upon one of the great mysteries in astronomy today---how were the first stars created and where are they?

Stars do not from from just dust. They are primarily made out of hydrogen, helium, and other gases. The early universe contained lots of hydrogen and helium, and so this is what the first stars were made of. As a star lives its life, it burns the hydrogen through thermonuclear reactions turning it into helium. Stars which are more massive than the Sun burn the helium into carbon, nitrogen, and oxygen. The most massive stars make even more massive elements like silicon and iron. When a star goes through its planetary nebula stage or goes supernova, it introduces all these elements into the surrounding interstellar medium. The stars that form from then on contain more of these "heavier" elements than their predecessors.

So the very first stars formed from just the hydrogen and helium created during the Big Bang. We, however, have not seen any of these stars! They are called Population III stars and have yet to be observed anywhere in our galaxy. We suspect they are out there and many astronomers are looking for them.

Keep and eye out for their discovery in the near future!

Great question!

[One of the key things that dust (or the elements from which dust is made) does during the formation of a star is allow the collapsing material to cool. The clouds of gas from which stars form are typically too hot for them to collapse to stars. Without some means to cool internally, the clouds would never collapse. Because the elements from which dust is made have many more electrons than hydrogen, there are more electron transistions within these atoms. More electron transitions means more ways for these atoms to emit radiation. More ways to emit radiation means more ways to cool. After all, radiation is energy, and the cloud needs to lose energy to collapse. Because there was no dust when the first stars formed, some astronomers have speculated that the first stars may have been quite massive. Because hydrogen is very inefficient at cooling, the first stars might have had to form from quite massive clouds. Only if the clouds were quite massive would they have overcome their internal energies (i.e., heat). Moderator]

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