1Steady State Theory
Universe has always existed as it is seen now
Density of galaxies remains the same as universe expands
Because new galaxies form in between galaxies that move apart
2The Big Bang Theory
Universe started from a single point
It exploded from a hot and dense state (13.8 billion years ago)
And expanded rapidly
Density of galaxies falls as universe expands
Because the space between galaxies expands
3Two key pieces of evidence in support of The Big Bang Theory
Galactic red-shift
Cosmic Microwave Background Radiation (CMBR)
4Explain how galactic red-shift supports the Big Bang Theory (6 marks)
Light from distant galaxies has a higher wavelength (red-shift)
This shows that galaxies are moving away from Earth
More distant galaxies show a greater red-shift, meaning they are moving away faster
This shows that the universe is expanding, so the Universe must have started from a single point
5 Explain how CMBR supports the Big Bang Theory (6 marks)
CMBR is observed uniformly
It was emitted when the universe formed (during the Big Bang)
The wavelength of the radiation has increased, due to the expansion of the universe
The temperature of the radiation has decreased, so the Universe must have started with a hot explosion
6Which is the currently accepted explanation for the origin of the universe and why?
The Big Bang Theory
There is more evidence supporting the Big Bang theory than the Steady State theory.
7 What happens when a wavesource is moving relative to an observer?
(The Doppler effect)
As the wavesource moves closer, wavelength decreases and frequency increases (blue-shift)
As the wavesource moves away, wavelength increases and frequency decreases (red-shift)
8 Which theories does galactic red-shift support?
Both the Big Bang theory and Steady State theory
Galactic red-shift suggests that galaxies are moving away from Earth and each other
In both theories the universe is expanding
9 Which theories does CMBR support?
Only Big Bang Theory
CMBR has the same profile as radiation from hot body that has cooled down over a long time
The temperature of the radiation has decreased, so the Universe must have started with a hot explosion
10 What discovery led to the Big Bang Theory becoming the currently accepted model?
CMBR
11What are meant by Solar Mass Stars?
Stars that have a mass similar to the mass of the Sun
12 Name the 6 stages in the life-cycle of a Solar Mass Star
Nebula
Protostar
Main Sequence Star
Red Gaint
White Dwarf
Black Dwarf
13What is a Nebula?
A giant cloud of hydrogen gas and dust
All stars are formed from nebulas
14 What causes a Nebula to become a Protostar?
The force of gravity pulls more particles closer together
Forming a hot ball of gas known as a Protostar
15What happens as the particles in a Protostar get pulled closer together?
Density increases, meaning more frequent collisions
This causes the temperature to increase
16When does a Protostar become a Main Sequence Star?
When the protostar becomes hot enough
Fusion reactions occur and the star reaches equilibrium
At this point the star is born and becomes a main sequence star
17What is meant by a star being in equilibrium?
The star is stable
The inward force due to gravity = outward pressure force from thermal expansion due to fusion
18What fusion reactions occur in a main sequence star?
Hydrogen nuclei fuse into hydrogen
19What causes a main-sequence star to become a red giant?
As the hydrogen is used up, fusion reactions die down
This causes the core to shrink (more collisions) and heat up again
Fusion reactions start again and star becomes stable
Outer part of the star expands, cools down and becomes red
20In a red giant, why does the core shrink initially?
As fuel runs out, less fission reactions occur
The inward force due to gravity is greater than outward pressure force from thermal expansion due to fission
21 What are the fusion reactions that occur in a red giant once the core shrinks?
Helium nuclei fuse into heavier elements
22 In a red giant, what happens when the helium is used up?
Fusion reactions stop for good
No outward pressure force from thermal expansion due to fusion
Gravitational forces compress inner layers into a hot, dense white dwarf
Outer layers form a planetary nebula which drifts out into space
23What causes a white dwarf to turn into a black dwarf?
The white dwarf appears white because of the energy left over from fusion
As energy is lost, it will fade into a black dwarf
24What happens to a star as its temperature starts to increase?
The outward pressure due to thermal expansion will increase
So the star will expand
25What happens to a star as its temperature decreases?
The outward pressure due to thermal expansion will decrease
So the star will contract/shrink
26What is meant by a High Mass Star?
A star that has a much greater mass (is much larger) than the Sun
27Compare the life-span of a Solar Mass Star and a High Mass Star
High Mass Stars have a much shorter lifespan than Solar Mass Stars
28Name the 6 stages in the life-cycle of a High Mass Star
Nebula
Protostar
Main Sequence Star
Red Supergiant
Supernova
Neutron Star or Black Hole
29 In high mass stars, what happens during the red supergiant stage?
After hydrogen is used up, the core shrinks and heats up
Until helium is able to fuse to create heavier elements
After helium is used up, the core shrinks and heats up again
Meaning heavier elements are able to fuse and cycle repeats
30 What are the fusion reactions that occur in a red supergiant when helium is used up?
Carbon fuses into oxygen
Oxygen fuses into nitrogen
Nitrogen fuses into heavier elements
Heavier elements fuse into iron
31In a red super-giant, why is iron the heaviest element that is formed?
Fusion of iron requires an energy input
32 In a red supergiant, what happens once all fusion reactions stop?
Outer layers of star quickly collapse due to gravitational force
This results in a shockwave explosion (supernova)
Outer layers are ejected into space
33 What happens to the material ejected from a supernova?
Forms a cloud of dust and gas which creates new stars and planets
34What is left following a supernova?
A neutron star
Or
(If the star was very massive) a black hole
35Features of a neutron star?
Extremely dense
Extremely small (few kilometres in diameter)
Made entirely from neutrons
36Features of black holes
Microscopically small
Incredibly strong gravitational field
Densest objects in universe
So dense light cannot escape
37Historically, why was astronomy important for humans?
Constellations were used for navigation
Positions of stars and sun used to track seasons for agriculture
38What did early telescopes allow astronomers to do?
Observe features of planets and moons
Develop more accurate models of the solar system (like the heliocentric model)
39Why are modern telescopes more useful to astronomers?
They can detect more wavelengths/frequencies of EM spectrum (not just visible light) and weaker signals
They can be positioned above the Earth’s atmosphere
They are more powerful (greater magnification)
Computers can process and improve data
40 What are the advantages of space telescopes?
They can detect radiation which is absorbed by Earth’s atmosphere
Clearer images - not affected by light pollution or weather
Produce much more detailed/magnified images
41What are disadvantages of space telescopes?
Much harder to repair
Very expensive
Limited size as must fit on a rocket