Question of the day: vacuums

So, in the vacuum of space there’s nothing, not even air.
Part one of my question is: why don’t the things that do exist in space (eg planets, stars etc) just explode in order to try and fill that vacuum? Is it just gravity that stops this happening?
Part two of my question is about the small scale spaces where there is nothing, ie between the nucleus and the electrons within an atom.  If most solid material is actually mostly made of those gaps, how do we (and all solid things) not just implode in order to get rid of that empty space?

If you can answer these, please do so in a comment – thank you!

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