I never thought about this before.. but how is it possible that there is gas in a vacuum?
The gas is gravitationally bound to itself. Also some dust and other debris keeping it from dispersing equally throughout space.
When the gas is disturbed enough that it coalesces, when it becomes dense enough, that is how stars form.
Space is not empty. Even in the areas we consider "empty," there's a few hydrogen atoms in every cubic meter of space. So it all depends on your definition of "a vacuum."
Not unlike "weightlessness." Which doesn't exist, because gravity never stops. It's everywhere, even if only weakly. If there were only two heavenly bodies, and they were on the opposite sides of the universe, eventually they would crash into each other because of their gravities.
Nonetheless, back when NASA still could find its ass in the dark, Walter Crankcase used to go on TV and regale us with stories of "weightlessness" and "the emptiness of space," and people believed him. Still do.