Expert: Tom Whiting - 10/29/2007

Question
Dear Mr.Whiting,
    For school we are conducting research about stars. We have already found out that in a galaxy there is a lot of dust and gas. Then because of gravity the dust and gas form a cloud. The cloud of dust and gas then experiences a nuclear fusion. The star is then born. But we would like to know, where the gas and dust from the galaxy comes from. Could you tell us where the gas originated from?

Thank-you in advance,
Sincerely,
From the students of Mr.Sylvestre's class.  

Answer
Hi Emily,
We need to separate your question into 2 parts the dust ......and the gas.

Well, for starters, you left one important step out of the
star formation recipe....you should have said...."The clouds
of dust and gas then experience.... contraction, compression, and heating..... and after a few million years the huge ball of dust and gas gets so hot in the core that it triggers off nuclear fusion in the center, and thus a star is born."

Then some very massive stars, stars 10 - 100 times the mass of the sun, live out a very short life, say only 10-30 million years  (That's SHORT TIME compared to solar-type stars with lifespans of 10 billion years!)  and then EXPLODE....we call this event a supernova.....that is where your dust comes from in your original question.

The gas part is easy.  The gas is mainly hydrogen and helium
and that came from the original Big Bang...the formation of the entire Universe 13.7 billion years ago.  In fact, hydrogen
and helium were the only gases  (substances) that the Big Bang  produced.....everything else, all the other elements-- Lithium #3 to Uranium #92-- were created by fusion inside the cores of subsequent stars that formed out of the gas from the
Big Bang.  Those very early, massive, Type III stars as they
are called, made up of strictly hydrogen and helium (no
heavier elements) no longer exist, having all exploded,
creating the heavier elements by fusion....the dust of today.....
and creating you and me and the Earth...WE are all, at least
in the physical sense, products of stardust of past, old supernovae stars, because that's where all the heavy
elements....iron, calcium, oxygen, carbon, etc. (Lithium 3  to Uranium 92)....came from.
{That's what nuclear fusion means...fusing--(combining)  hydrogen and helium gas up to heavier elements, first carbon, and oxygen, and silicon, and iron, and all the way up to uranium!}

So the gas, hydrogen and helium, came to us directly from
the Big Bang, and the dust part came from exploded stars
of the past, enriching the original H -He gas with "dust"...the
heavier elements of carbon, iron, nickel, silicon, etc.   Then
stars like the sun  (Type I stars) formed out of this new
gas-dust mixture....along with the Earth, Solar System, and
you and me.  Look around you and all you see is supernova
remnant dust, because that is what everything is made up
of, except for a little hydrogen and helium gas.

Hope all this helps,....and makes sense,
Clear Skies,
Tom Whiting
Erie, PA