Hello guys I am sanam.
dark matter are the unknown substance that we don't know what is this .But we are at least sure that they exist in the universe and contain about 85 percent of mass of the universe .when scientists were calculating the mass of the galaxy it came very high but actually there is no such huge mass present and in this way scientists gives the term dark matter.
And the universe is accelerating .What is the reason that universe is accelerating continuously and this gave birth to dark energy which makes the galaxy and space stretched or accelerated.