Astrophysics

• Our solar system is part of the Milky Way galaxy
• Planets in our solar system

  Eight (plus the dwarf planets)
• What the planets orbit around

  The sun
• Type of body the sun is

  A star
• Force that pulled together the cloud of dust and gas to form the sun

  Gravitational force of attraction
• Cloud of dust and gas

  A nebula
• Reactions that take place at the start of a star's life cycle

  Fusion reactions
• Factor that determines the type of lifecycle a star undergoes

  The size of the star
• Phases all stars of the same or greater size than the sun undergo

  • Protostar phase
  • Main sequence phase
• What stars of a similar magnitude to the sun become at the end of their life-cycle

  A black dwarf
• What stars much bigger than the sun can become at the end of their lifecycle

  • Neutron star
  • Black hole
• Phases stars of similar size to the sun go through between being a main sequence star and a black dwarf


  • Red giant
  • White dwarf
• Phases stars of greater size than the sun go through between being a main sequence star and a neutron star/black hole


  • Red super giant
  • Supernova
• All of the naturally occurring elements are produced during the fusion processes in a star
• Condition required for fusion reactions to occur in a star

  Very high temperatures
• How elements heavier than iron are produced

  In a supernova
• Type of nuclei that fuse together to form heavier elements in a star

  Hydrogen nuclei fuse to form heavier elements
• How elements are distributed throughout the universe

  Through the explosion of a massive star (supernova)
• What allows planets and satellites to maintain circular orbits

  • Gravity provides the gravitational force that acts as the object's centripetal force
  • The presence of a centripetal force allows for the object to maintain its circular orbit
• Red-shift


  An observed increase in the wavelength of light from distant galaxies
• The further away a galaxy is

  The faster it is moving
• Type of satellite a planet's moon can be described as

  A natural satellite
• The further away a galaxy is

  The greater the observed increase in wavelength
• Examples of artificial satellites


  • TV satellites
  • Satellites used for satellite imaging
• Red-shift provides evidence that the universe is expanding
• Red-shift supports the Big Bang theory
• Explain why for a stable orbit, the radius of orbit must change if the speed changes

  1. At higher speeds, the object requires a greater centripetal force

  2. For a greater centripetal force, the gravitational force must increase

  3. This is achieved by the radius of the orbit being reduced
• Big Bang theory


  The entire universe started from a very small, hot and dense region in space
• Explain how the force of gravity acting on a satellite affects its speed and velocity

  1. The force can alter its velocity since the direction is continually changing

  2. It can't cause a change of speed since there is no force component in the direction of motion
• The galaxy that is further away


  Is travelling faster
• Scientists observed supernovae, which suggested that galaxies are moving away at an ever faster rate
• Prior to observations of supernovae, the rate of expansion was expected to occur at an ever slower rate due to gravitational forces
• The existence of energy and mass that we can't detect, known as dark matter and dark energy, could explain the universe's ever increasing rate of expansion
• These ideas about dark matter and dark energy are still being developed by scientists and are not yet fully understood
• Exam Question: Describe what is meant by red-shift.

  the (observed) increase in wavelength (of light from galaxies) as galaxies move away from us
• Exam question: Compare the formation and life cycles of stars with a similar mass to the Sun to stars with a much greater mass than the Sun (6) P1

  all stars: • form in a cloud of gas and dust (nebula) by gravity – mostly hydrogen • forms a protostar • Fusion begins
• Exam question: Compare the formation and life cycles of stars with a similar mass to the Sun to stars with a much greater mass than the Sun (6) P2

  • fusion of small nuclei into larger nuclei (hydrogen into helium) • main sequence star – stable period where gravitational forces (inwards) balance forces (outwards) due to fusion processes
• Exam question: Compare the formation and life cycles of stars with a similar mass to the Sun to stars with a much greater mass than the Sun (6) P3

  comparisons: • stars about the same size as the Sun expand to become a red giant, stars much bigger than the Sun expand to become a red supergiant • stars about the same size as the Sun contract (and temperature increases) to become a white dwarf, stars much bigger than the Sun explode in a supernova
• Exam question: Compare the formation and life cycles of stars with a similar mass to the Sun to stars with a much greater mass than the Sun (6) P4- final

  • stars about the same size as the Sun (cool to) become a black dwarf, stars much bigger than the Sun become either a neutron star or black hole