Dark energy and Dark matter

Dark matter

• 25% of the Universe

• Velocity of stars expected to decrease after an initial increase with distance from a galaxy (inverse square law), as all mass thought to be concentrated at the centre. However, the velocity of stars did not decrease with distance from the centre of the galaxy.

• TL;DR Gravity of seen matter not strong enough to form galaxies (would form stars scattered about) therefore must be matter that cannot be seen.

• Neither emits nor absorbs EM radiation (cannot be seen)

• Has mass and therefore is affected by gravity.

• NOT THE SAME AS A BLACK HOLE.

• Has been detected: places with high concentration of dark matter bend light that passes near (must interact with gravity)

Dark energy

• 70% of the Universe

• Light from supernova Ia observed to be less intense than expected.

• So concluded that the expansion of the Universe was accelerating.

• Dark energy thought to be causing the expansion of the Universe to accelerate.

• Has not yet been detected.