• Dark matter doesn't emit light, so we can’t see it.
  • We know it is there because it affects the motion of objects around it.
  • Dark matter could just be ordinary matter, like what makes up Earth.
  • The Universe could contain lots of objects that don't have enough mass to glow on their own.
  • There might just be a lot of black holes.
  • Most scientists think that ordinary matter is less than half of the total matter in the Universe.
  • Astronomers have discovered that the Universe is expanding even faster than before.
  • What is causing the expansion to accelerate?
  • Astronomers call this dark energy.
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