First things first: There is a simple rule (yes, rule, not mere suggestion) about when to use further versus when to use farther. The former is for figurative distance (“How much further can this nonsense go on?”), whereas the latter is for literal distances (“How much farther is it to Grandma’s house?”). Because the example sentence deals with real distances, change further to farther.
Also, don’t capitalize universe.
I recommend changing 90% to ninety percent.
(Fun fact: We cannot be certain those are the farthest galaxies, because ones farther away would be traveling, relative to us, at more than lightspeed, so we currently have no way of detecting them if they exist. This should not be mistaken for proof that such galaxies do not exist. That’s why I’m adding detectable to the example sentence.)
The farthest detectable galaxies in the universe are speeding away from us at more than ninety percent of the speed of light.