Exact same thing just happened to me, first time the game crashes on me since Supernova came out. I thought it was my computer overheating due to the size of the galaxy and number of objects in my late game but I am reading messages that it is happening quite a bit. Frogboy just said in the Steam forums that same thing just happened to him, it is an update to the Steam achievements that apparently did it, fix coming within the next few minutes.
