Dark energy

Dark energy constitutes 70% of the universe's mass energy and is responsible for the accelerating expansion of the universe, counteracting the effects of gravity. It is the most accepted explanation for these phenomena.

What percentage of the mass energy of the known universe is accounted for by dark energy?

What unexpected observations led to the suggestion of dark energy's existence?

How is the expansion of the universe characterized after the Big Bang?

What is the effect of dark energy on gravity?

What is considered the best explanation for dark energy?