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AQA GCSE Physics 3-4 Stars & Space


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). – PowerPoint PPT presentation

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Title: AQA GCSE Physics 3-4 Stars & Space

AQA GCSE Physics 3-4Stars Space
  • GCSE Physics pages 266 to 275

April 10th 2010
AQA GCSE Specification
  • 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
  • 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

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.

  • 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.

Types of galaxy
Classifying galaxies
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.
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
  6. Copy the Key points table on page 267.
  7. Answer the summary questions on page 267.

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
  • (ii) The Universe has expanded leaving these
    vast spaces.

  • 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.

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

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.

  • 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.

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.

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.

The future of the SunMain sequence
  • The Sun is about half way through a 10 billion
    year period in its life cycle called main
  • 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.

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.

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
  • The white dwarf will gradually cool over billions
    of years to form a black dwarf.

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
  • The nearest star to the Sun is a red dwarf called
    Proxima Centauri. It is just over 4 light years

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.
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

  • 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.

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.

Black holes
  • The most massive stars collapse to form black
  • 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.

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.
Star evolution summary
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.
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.

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
  • 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
  • (ii) The gravitational field is so strong that
    nothing can escape from it.

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.

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

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.

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.
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.

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.

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!

  • 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.

Universal issues Notes questions from pages 272
  • Answer questions (a), (b) and (c) on page 272.

Universal issues ANSWERS
  1. 2 km
  2. 9000 km
  3. over 30 million km

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.
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