ODU : The Expanding Universe Flashcards
Doppler Effect
The change in frequency observed when a source of sound (or light) waves moves relative to an observer.
Red Shift
When light from stars or galaxies that are moving away from us is shifted to longer (more red) wavelengths. It is an example of the doppler effect
Blue Shift
When light from stars or galaxies moving towards us is sifted to shorter (more blue wavelengths)
Rcessional Velocity
The velocity of an object that is moving away from the observer
Hubbles law
- The bigger the magnitude of shift, the greater the speed the galaxy was moving away from the earth
- The further away the galaxy is the greater the speed it is travelling at.
Dark Matter
A considerable amount of matter in galaxies that we cannot see.
It accounts for the observation of unusually high orbital speeds of stars on the outer arms of galaxies.
It is thought to make up around 22% of all matter in the universe.
Dark energy
A source of energy capable of producing a force which acts against the gravitional force of attraction, pushing matter apart.
It accounts for the observation that the expansion of the universe is still accelerating.
It is thought to make up around 74% of all matter in the universe
Temperature and wavelengths of Stellar objects (recessional velocity)
The peak wavelenth is shorter for hotter objects than for cooler objects.
Hotter objects emit more radiation per unit surface area per unit time (irradiance) than cooler objects.
Cosmic Micorwave Background Radiation (CMBR)
Evidence for the Big Bang.
CMBR is background radiation coming from all direction in space.
It is thought that this is radiation left over from an early stage in the development of the Universe that has increased in wavelength (towards to the microwave part of the EM-spectrum) due to the expansion of the universe.
Olber’s Paradox
Evidence for the Big Bang.
If the universe was infinitely old and contained an infinite numbe of stars, then the night sky should be white due to stars being visible in any line of sight.
Since the Big bang theory supports the idea of an expanding Universe, only light from stars within the observable Universe will reach us.
The big Bang theory gives a finite age to the Universe and explains the darkenss of the night sky.
Red Shift in Galaxies
When we observe galaxies we see that most of them are Doppler red-shifted rather than blue-shifted.
This is evidence that universe is expanding (moving away from a central point)
The abundance of Hydrogen and Helium in the Universe
The most abundant elements in the universe are hydrogen (-75%) and helium (-25%).
The abundance of helium in the universe cannot be explained by being made inside stars.
Most of helium remains locked up in their cores.
However, the abundance of helium can be accounted for by being formed during the first 17 minutes (or so) after the Big Bang.
