The Big Bang Theory
- The universe began as a violent expansion of a single point of pure energy in an instant, where all matter and space were created
- Universe was a seething mass of radiation in which matter and anti- matter were being created and destroyed
- Three minutes after the Big Bang: universe has cooled enough for the creation of protons and neutrons which formed the nuclei of the first few elements- hydrogen, helium and tiny amounts of lithium
- 300, 000 years after the Big Bang: the fog of thick radiation cleared. The nuclei of the atoms combined with electrons to form the first elements
- Billion years after the Big Bang: atoms became clumped together by the pulling force of gravity, producing galaxies.
Quasars:
super large galactic cores that put out more light than galaxies
- Only found 10- 15 billion light years away, nothing exists past them
Evidence of the Big Bang Theory:
- Cosmic microwave radiation: afterglow of the enormous amount of heat produced during the Big Bang.
- Universe expanding
Red shifts: When the star is moving away, light that reaches Earth has a longer wavelength (universe is expanding). Implies that if you run things in reverse, everything must have come from the same location. - Quasars: are objects from the past that indicate the structure of the universe is very different today thus disproving the steady state theory
- Amounts of hydrogen and helium present in universe fitted exactly the predictions from Big Bang
Steady state theory:
- Has no beginning or end. New matter must be formed to keep the density equal over time.
- Universe has always existed and always will, and no beginning or end. Matter was continuously being created in the universe at an enormous rate causing the universe to expand.
Why do astronomers say the universe has evolved?
The universe continues to evolve, as the Universe does not stay the same but is gradually changing e.g. life cycle of stars, and the constant
Open universe model: (Continuous universe)
- When matter is less than the amount required to keep the universe stable, universe continues to expand
o Because there is not enough matter, and therefore not enough gravitational force to halt the expansion - Stars will die, the universe will become dark and cold
Closed universe model: (Pulsating universe)
- When there is more matter than the amount of required to keep it stable, universe will eventually stop expanding and start to contract (big bang in reverse)
- Big crunch
Flat universe model:
- Expansion of universe will become balanced by the forces of gravitational attraction between matter
- Universe will be at rest and stay this way.
The life cycle of low mass stars
- A star is ‘born’ from a nebula
- Cloud of gas in nebula collapses on itself under its own gravity, forming a protostar
- As more material is packed into the protostar, core becomes very hot allowing nuclear fusion
- There in the core hydrogen fuel is converted into helium
- Hydrogen runs out, fusion reaction occurs in shell around the core. Helium produced through nuclear fusion, fuses into heavier elements e.g. carbon and oxygen.
- Cores shrinks and outer layers of the star expand and cool, forming a red giant
- Outer region of the red giant are blown out into space, leaving a planetary nebula
- Without outward force of nuclear reaction, it shrinks to form a white dwarf
- Radiate their heat and cool off to become black dwarfs
The life cycle of large mass stars:
- A star is ‘born’ from a nebula
- Mass in large stars create enormous gravitation force in the core. Nuclear fusion rapidly occurs creating hot bright stars
- As the star matures, hydrogen fuel is used to form a red super giant
- After the fuel is used up and without the outward force of nuclear reaction, core collapses in a second causing a supernova.
- Either forms a black hole or dense neutron star depending on its mass
On what basis are stars categorised?
Stars are classified by their spectra (the elements that they absorb) and their temperature.
Nuclear fusion:
is an atomic reaction that fuels stars. In fusion, many nuclei (the centre of atoms) combine together to make a larger one (which is a different element). The result of this process is the release of a lot of energy
