What lies between the galaxies?
Intergalactic space is what lies between the galaxies and many experts believe it to be filled with some kind of super-thin gas.
Then again, there is also the theorised dark matter, the mysterious substance that emits neither light nor radiation and is estimated to account for around 85% of the matter in most galaxies.
Recent breakthroughs at the Large Hadron Collider could one day throw much more light on this and other questions about the formation and structure of the universe – but until someone accurately measures either dark matter or intergalactic space itself, it’s all just theory.
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Plus, take a look at:
What happens when galaxies collide?
How old is the Andromeda galaxy and how did it form?
How many stars are there in the universe?