Dark Energy & Dark Matter
Dark Energy
- Scientists know that the universe is accelerating as it expands
- Dark Energy is a hypothetical form of energy which is used to try and explain the accelerating expansion
- Dark energy is defined as:
A type of energy that permeates the whole universe and opposes the attractive gravitation force between galaxies via the exertion of a negative pressure
- Dark energy cannot be detected directly
- It should make up 68% of the total energy in the universe
- So far experiments have not been able to find the form of the energy
Dark Matter
- Astronomers expect to observe the velocity of an object within a galaxy decrease as it moves away from the galaxy’s centre
- This is thought to be the case because of weakening gravitational field strength further from the centre
- This is observed in smaller mass systems, such as the in the solar system, where planets orbiting furthest from the Sun have the slowest orbital velocity
- This is not the case in larger mass systems, such as entire galaxies
- In fact, mass is not concentrated in the centre of galaxies - it is spread out
- However, all the observable mass of a galaxy is observed to concentrate in the centre of galaxies
- Therefore, there must be another type of matter that can't be observed
- This is known as Dark Matter
- Dark matter is defined as:
Matter which cannot be seen and that does not emit or absorb electromagnetic radiation
- Dark matter cannot be detected directly through telescopes
- It is estimated to make up 27% of the mass in the universe
- It is detected based on its gravitational effects relating to either the rotation of galaxies or by the gravitational lensing of starlight
