Summary:
- 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.