AQA GCSE Physics 3-4 Stars & Space

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AQA GCSE Physics 3-4Stars Space

• GCSE Physics pages 266 to 275

April 10th 2010
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AQA GCSE Specification

• STARS GALAXIES
• 13.10 What is the life history of stars?
• Using skills, knowledge and understanding of how
  science works
• to explain how stars are able to maintain
  their energy output for millions of years
• to explain why the early Universe contained
  only hydrogen but now contains a large variety of
  different elements.
• Skills, knowledge and understanding of how
  science works set in the context of
• Our Sun is one of the many millions of stars
  in the Milky Way galaxy.
• The Universe is made up of at least a billion
  galaxies.
• Stars form when enough dust and gas from space
  is pulled together by gravitational attraction.
  Smaller masses may also form and be attracted by
  a larger mass to become planets.
• Gravitational forces balance radiation
  pressure to make a star stable.
• A star goes through a life cycle (limited to
  the life cycle of stars of similar size to the
  Sun and stars much larger than the Sun).
• Fusion processes in stars produce all
  naturally occurring elements. These elements may
  be distributed throughout the Universe by the
• explosion of a star (supernova) at the end of its
  life.

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The Milky Way

• The Milky Way is the name of our galaxy.
• From Earth we can see our galaxy edge-on. In a
  very dark sky it appears like a cloud across
  the sky resembling a strip of spilt milk.

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Galaxies

• Galaxies consist of billions of stars bound
  together by the force of gravity.
• There are thought to be at least 200 billion
  galaxies in our Universe each containing on
  average 2 billion stars.

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Types of galaxy
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Classifying galaxies
7
Choose appropriate words to fill in the gaps
below The ___________ is made up of billions of
galaxies which consist of __________ of stars
bound to each other by the force of
___________. The name of our _________ is The
Milky Way. The ______ is located towards the
outer edge of our galaxy. The are different types
of galaxy ________, barred-spiral, elliptical
and irregular. The Milky Way is a ____________
galaxy. The _____________ Galaxy is the nearest
spiral galaxy to the Milky Way.
Universe
billions
gravity
galaxy
Sun
spiral
barred-spiral
Andromeda
WORD SELECTION
spiral
galaxy
barred-spiral
Andromeda
gravity
billions
Sun
Universe
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GalaxiesNotes questions from pages 266 267

1. (a) What is a galaxy? (b) Name our galaxy. (c)
   How many galaxies are there?
2. Copy and answer question (a) on page 266.
3. Outline the history of the Universe to the
   present day.
4. Explain the part played by gravity in the
   evolution of the Universe.
5. Copy and answer questions (b) and (c) on page
   267.
6. Copy the Key points table on page 267.
7. Answer the summary questions on page 267.

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Galaxies ANSWERS

• In text questions
• When we use a powerful telescope to see a distant
  galaxy, we are seeing the galaxy as it was
  billions of years ago because the light from it
  has taken billions of years to reach us.
• About 13 billion years.
• They are both positively charged, so they repel
  each other. The force of repulsion is much
  greater than the force of gravity between them.

• Summary questions
• 1. (a) Expanded, cooled.
• (b) Attracted.
• (c) Formed.
• 2. (a) (i) We could not send a probe far enough.
• (ii) Galaxies take millions of years to form we
  couldnt wait that long.
• (b) (i) Gravitational forces hold the stars
  together.
• (ii) The Universe has expanded leaving these
  vast spaces.

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Stars

• A star is a massive, luminous ball of gas that is
  held together by gravity.
• The Sun is a typical star that consists of about
  75 Hydrogen, 24 Helium and 1 other elements
  such as carbon and oxygen.
• There are about 2 billion stars in our galaxy.

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Stars colours

• The colour of a star depends on its surface
  temperature.
• The Sun is an average temperature yellow star.

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The birth of the SunNebula

• Stars usually form inside a nebula.
• This is a cloud of mostly hydrogen along with
  smaller amounts of other elements dust.

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Protostar

• Due to gravitational attraction, the gas and dust
  clumps together.
• Gravitational potential energy is converted into
  heat energy.
• The gas starts to glow forming a protostar.

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Nuclear fusion

• When the temperature rises above about 10
  millionC hydrogen nuclei join together to form
  Helium by the process of nuclear fusion.
• Energy is released.
• The star becomes stable when the radiation
  produced causes an outward pressure that prevents
  further gravitational collapse of the star.

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The birth of the solar system

• About 99.9 of the original gas and dust formed
  the Sun. The remaining 0.1 formed the planets
  and other bodies of the solar system.

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The future of the SunMain sequence

• The Sun is about half way through a 10 billion
  year period in its life cycle called main
  sequence
• During this time hydrogen in the core of the Sun
  is converted into Helium by the process of
  nuclear fusion.
• The Sun will gradually become hotter over time so
  that in about two billion years time life will no
  longer be possible on Earth.

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Red Giant

• In about 5 billion years time the hydrogen in the
  Suns core will run out.
• Without outward radiation pressure the core will
  collapse under gravity and become even hotter.
• Eventually the temperature will be high enough to
  cause the fusion of helium into heavier elements
  such as carbon and oxygen.
• The now greater outward radiation pressure will
  cause the Sun to expand into a Red Giant.

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Planetary Nebula and White Dwarf

• After only a few million years the Helium will
  also run out in the Suns core.
• A final collapse of the core occurs to form a
  very hot dense object about the size of the Earth
  called a white dwarf.
• The rest of the Sun is blown away to form a
  planetary nebula (from which a new star might
  form).
• The white dwarf will gradually cool over billions
  of years to form a black dwarf.

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Low mass stars

• The Sun is an average star.
• There are many cooler stars of lower mass called
  red dwarfs.
• These are very faint and can only be seen through
  telescopes.
• The nearest star to the Sun is a red dwarf called
  Proxima Centauri. It is just over 4 light years
  away.

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High mass stars

• Most of the stars we can see in the sky are more
  massive than the Sun.
• Compared with the Sun they
• - are larger
• - are brighter
• - are bluer when main
• sequence
• - pass through their life cycles
• more quickly
• - sometimes end their lives
• differently

All the main stars in the constellation of Orion
are more massive than the Sun.
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Red supergiants

• Higher mass stars form larger red giants.
• The star Betelgeuse (top left in Orion) is larger
  than the orbit of Mars about the Sun.
• Supergiants will also cause elements such as
  carbon and oxygen to undergo nuclear fusion to
  form even heavier elements such as silicon and
  iron.

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Supernovae

• When a red supergiant star causes iron in its
  core to undergo nuclear fusion energy is absorbed
  causing a great implosion.
• This rebounds and causes a massive explosion that
  can for a few days outshine a whole galaxy. This
  is called a supernova.
• Supernovae are very rare. They can be seen in the
  daylight sky. The last observed supernovae in our
  galaxy took place in 1604.

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Neutron stars

• The core left over from a supergiant star can be
  so massive that gravity causes electrons and
  protons to combine to form neutrons. This is a
  neutron star.
• A neutron star is only about 10km in diameter and
  is extremely dense. A teaspoon full of neutron
  star has a mass of about two billion tonnes.
• Some neutron stars, called pulsars, emit regular
  radio signals.

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Black holes

• The most massive stars collapse to form black
  holes.
• The gravity caused by black holes is so strong
  that nothing can escape, including light.
• Black holes can only be observed from the affect
  they have on surrounding objects such as a
  companion star.

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The life cycle of the Sun
NOTE Due to its relatively low mass the Sun will
not become a red supergiant, supernova, neutron
star or black hole.
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Star evolution summary
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Choose appropriate words to fill in the gaps
below Stars are made mostly from __________ and
generate their energy by nuclear _________. Stars
are formed in nebulae when ________ causes gas
and dust to clump together. Towards the end of
its life, the Sun will _________ to form a red
giant after which most of its material will be
blown away as a planetary ______ leaving behind a
small white _____ star. More ________ stars than
the Sun may undergo a supernova explosion and
become _________ stars or black holes.
hydrogen
fusion
gravity
expand
nebula
dwarf
massive
neutron
WORD SELECTION
expand
massive
hydrogen
neutron
nebula
gravity
fusion
dwarf
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The life history of a star Notes questions from
pages 268 269

1. Copy Figure 2 on page 269.
2. Outline the life history of a star like our Sun.
   Your account should include what is meant by (a)
   protostar, (b) red-giant, and (c) white dwarf.
3. Explain the additional stages undergone by the
   most massive stars. Your account should include
   what is meant by (a) supernova, (b) neutron star,
   and (c) black hole.
4. (a) How does a star produce energy? (b) Explain
   why the Sun is neither expanding or contracting
   at the present time.
5. Copy and answer questions (a), (b), (c) and (d)
   on pages 268 and 269.
6. Copy the Key points table on page 269.
7. Answer the summary questions on page 269.

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The life history of a star ANSWERS

• In text questions
• The potential energy of gas and dust decreases
  when it gathers and is transformed into heat
  energy.
• The outward pressure of radiation from its core
  stops it collapsing.
• Gravity.
• Gravity.

• Summary questions
• 1. (a) B, A, C, D.
• (b) (i) A
• (ii) It will fade out and go cold.
• 2. (a) (i) Expand, collapse.
• (i) Explode, collapse.
• (b) (i) The neutron star must have sufficient
  mass.
• (ii) The gravitational field is so strong that
  nothing can escape from it.

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The formation of elementsHydrogen and helium

• Hydrogen and some helium was formed at the time
  of the Big Bang.
• Helium is also formed by nuclear fusion in main
  sequence stars like the Sun.

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Lighter elements

• Elements such as carbon, oxygen and silicon are
  formed by nuclear fusion in red-giant stars.
• The heaviest element formed in red-giants is
  iron.

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Heavier elements

• All elements heavier than iron are thought to
  have been formed during supernovae explosions.
• The fact that such elements exist on Earth is
  evidence that our Sun and the entire solar system
  has been formed out of the supernova explosion of
  an earlier star.

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Choose appropriate words to fill in the gaps
below The lightest and most common element in
the Universe is ___________. Hydrogen and some
__________ were formed from the Big Bang. Most
elements have been formed by nuclear _________ in
the cores of stars. Helium and the __________
elements such as _________ are formed by stars
like the Sun. Elements up to ______ are formed in
the core of red supergiant stars. The heaviest
elements are formed in ___________ explosions.
helium
hydrogen
fusion
lighter
carbon
iron
supernovae
WORD SELECTION
helium
hydrogen
supernovae
carbon
lighter
fusion
iron
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How the chemical elements formed Notes
questions from pages 270 271

1. Explain the two different processes by which (a)
   lighter and (b) heavier elements were formed.
2. Copy and answer questions (a) and (b) on pages
   270 and 271.
3. Outline the ways of trying to discover the
   presence of extra-terrestial life.
4. Copy and answer question (c) on page 271.
5. Copy the Key points table on page 271.
6. Answer the summary questions on page 271.

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How the chemical elements formed ANSWERS

• In text questions
• In a supernova explosion.
• Its half-life is very short compared with the age
  of the Sun. Any plutonium formed when the Sun
  formed would have decayed long ago.
• Carbon atoms are in all the molecules that make
  up living objects.

• Summary questions
• (a) Hydrogen.
• (b) Uranium.
• (c) Helium, iron.
• (d) Hydrogen.
• 2. (a) Stars, supernova.
• (b) Supernova, galaxy.
• (c) Stars, supernova.

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The light year

• A light year is the distance travelled by light
  in one year.
• Light travels at 300 000 000 metres per second
• 300 000 kilometres per second
• 18 million kilometres per minute
• 1.08 billion km per hour
• 26 billion km per day
• 9.5 trillion km per year!

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Question

• Calculate the distance to the nearest star to the
  Sun, Proxima Centauri, in kilometres and how long
  it would take to reach it travelling at 100 km/h
  (60 mph) if this star is 4.2 light-years away.
• Distance 40 trillion kilometres (4.0 x 1012 km)
  
• It would take about 45 million years to reach
  this star.

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Universal issues Notes questions from pages 272
273

• Answer questions (a), (b) and (c) on page 272.

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Universal issues ANSWERS

1. 2 km
2. 9000 km
3. over 30 million km

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How Science Works ANSWERS

1. Myths how the Earth was created by Phan Ku.
2. Observations that the Sun, moon, planets and
   stars move across the sky.
3. The data concerning the size of the Moon.
   Ptolomys Earth-centred model required the Moon
   to speed up and slow down and hence therefore to
   change its size as seen from Earth. The Moon,
   when measured, did not show these changes in
   apparent size.
4. Example of hypothesis Anaxagoras hypothesised
   that the Sun and the Moon were made of rocks.

1. Ptolomys Earth-centred theory of the Universe.
2. Copernicus theory of the universe because it is
   supported by much evidence, but theories are not
   completely proven in all instances and therefore
   always open to being disproved. This is more
   obviously shown by Bruno. Planets are being
   discovered around stars, but there is no evidence
   of life outside of the Earth.
3. Anaxagoras and Bruno were examples of political
   influences on science.