Re: what fills in the empty space in outerspace? nitrogen?i am not sure.

Hi,

If it were really "empty space", then *nothing* would fill it, because it would be empty. In fact, of course, even the space between the stars is not perfectly empty. Spread out between the stars in our Galaxy, there's a collection of very thin gas and dust called the "interstellar medium". The density is pretty low, around 1 atom per cubic centimeter (compared to 10 billion billion molecules in a cubic centimeter of air at sea level), and it's mostly made up of hydrogen atoms. However, there's a whole lot of space in between the stars, so when you add up all those scattered atoms, you get enough hydrogen gas to make lots of stars, which in fact happens occasionally, as the interstellar gas collapses under its own gravity to form "clumps" which eventually become stars. Around 5 billion years ago, our own Sun formed from just such a clump.

The interstellar medium is found in the space between stars within our Galaxy. What about the much bigger spaces in between the galaxies ? Our galaxy is just one of untold billions in the Universe. What is in all the space between galaxies ? It turns out that intergalactic space is also not perfectly empty. Out between the galaxies you can find an even more tenuous collection of gas called the "intergalactic medium". It is even less dense than the interstellar medium, but there is so much space in between the galaxies that when you add up all the gas which is probably out there, it appears likely to be more mass than all the rest of the "ordinary" matter we find in galaxies.

You can read more about the interstellar medium at

http://www-ssg.sr.unh.edu/tof/Outreach/Interstellar/Interdepth.html
http://snoopy.gsfc.nasa.gov/~orfeus2/ism.html and
http://zebu.uoregon.edu/textbook/ism.html .

and you can read more about the intergalactic medium at

http://casa.colorado.edu/~mcl/igmproject.html and
http://www.sciam.com/1998/0398cosmos/0398veilleux.html.

If you want to talk about this further, you can reach me via the Mad Scientist Network.