Dark matter, dark energy

• Galaxy clusters-

  • Contain up to thousands of galaxies and are dominated by red and dead elliptical galaxies.
• Maps of galaxy positions reveal extremely large structures; superclusters and voids.
• How does structures form?

  through gravity
• Dark matter: form of matter that emits no light but we concluded its existence from its gravitational influence.
• Dark Energy: energy/ only source of repulsive force that is pushing the universe apart.
• dark matter is 23% of the universe
• dark energy is 73% of our universe.
• What is the evidence of dark matter in galaxies?

  flat rotation curves in spiral galaxies.
• We can measure the velocity of galaxies ina a cluster from their doppler shifts.
• Clusters contain large amounts of x-ray emitting hot gas.
• Gravitational lensing: the bending of light rays by gravity; tells us the cluster's mass.