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6.2.2Space Physics

Stars — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions

5 min read 10 parts Lesson 17 of 24 1 quiz

📚 Cambridge IGCSE Physics 0625 Hub / Topical Revision
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Lesson summary

6.2.2 Stars — IGCSE Physics Notes — IGCSE PHYSICS notes: Describe the life cycle of a star from nebula to its end stage and explain how the mass of a star decides its fate.Nebula — a giant cloud of gas and dust, mainly hydrogen, in which stars form.Protostar — gravity pulls parti…

  • Stable star
  • Main sequence
  • Low-mass star
  • High-mass star
  • More massive stars
  • Supernovae

Part 1 of 8Star formation

1Nebula
  • Nebula a giant cloud of gas and dust, mainly hydrogen, in which stars form.
2Protostar
  • Protostar gravity pulls particles together into a hot ball of gas.
  • Density increases, collisions become more frequent and the temperature rises.
3Stable star
  • Stable star when the core is hot enough, hydrogen fuses to helium, releasing heat and light.
  • Inward gravity is balanced by outward thermal pressure.
4Main sequence
  • Main sequence the long, stable stage of a star.

Part 2 of 8Mass decides the fate

Low-mass star
  • Low-mass star up to about 8 times the mass of the Sun, such as the Sun itself.
High-mass star
  • High-mass star more than about 8 times the mass of the Sun.
More massive stars
  • More massive stars use their fuel faster and have shorter lives.

Part 3 of 8Low-mass stars

1
Main sequence star fuses hydrogen to helium for several billion years.
2
Hydrogen runs out, the core shrinks and heats, and helium fuses to carbon.
3
The outer layers expand and cool, forming a red giant.
4
The helium runs out, the core collapses and the outer layers are ejected as a planetary nebula.
5
The remaining core is a white dwarf, which cools and emits less energy.

Part 4 of 8High-mass stars

1
Main sequence star lasts several million years.
2
Hydrogen runs out and the star expands into a red supergiant.
3
Successively heavier elements form by fusion, such as carbon, nitrogen and oxygen.
4
Fusion stops once iron forms, the core collapses and a supernova explosion follows.
5
The remnant is a dense neutron star.
6
In the most massive stars the neutron star collapses further to a black hole.

Part 5 of 8Origin of elements

Supernovae
  • Supernovae elements heavier than iron are formed in a supernova and are ejected into space.
Recycling
  • Recycling the nebula from a supernova may form new stars with orbiting planets.
Earth
  • Earth planets such as the Earth contain material made in earlier stars.

Part 6 of 8Black holes

Description
  • Description an extremely dense point in space.
Escape
  • Escape not even light can escape from it.

Part 7 of 8Stars and galaxies

Galaxy
  • Galaxy a collection of billions of stars.
Appearance
  • Appearance stars appear as points of light because they are so far away.

Part 8 of 8More from the specification

1
Stellar parallax distance measurement
  • Stellar parallax distance measurement measuring small angular shifts against background stars provides an astronomical means to compute stellar distances.
2
Life cycle of a star
  • Life cycle of a star a nebula collapses under gravity into a protostar, which becomes a main-sequence star once hydrogen fusion starts
3
Red giant and endpoints
  • Red giant and endpoints a low-mass star becomes a red giant,
  • then a white dwarf; a massive star becomes a red supergiant, a supernova,
  • then a neutron star or black hole
4
Redshift
  • Redshift light from distant galaxies has a longer observed wavelength because they are moving away
5
Hubble's law
  • Hubble's law the more distant a galaxy, the faster it recedes, which supports an expanding universe
6
Cosmic microwave background radiation
  • Cosmic microwave background radiation leftover radiation from the early universe, evidence for the Big Bang
7
Life cycle of a star
  • Life cycle of a star a nebula collapses under gravity into a protostar, which becomes a main-sequence star once hydrogen fusion starts
8
Red giant and endpoints
  • Red giant and endpoints a low-mass star becomes a red giant,
    • then a white dwarf; a massive star becomes a red supergiant, a supernova,
    • then a neutron star or black hole
9
Redshift
  • Redshift light from distant galaxies has a longer observed wavelength because they are moving away
10
Hubble's law
  • Hubble's law the more distant a galaxy, the faster it recedes, which supports an expanding universe
11
Cosmic microwave background radiation
  • Cosmic microwave background radiation leftover radiation from the early universe, evidence for the Big Bang
12
Light-year
  • The distance light travels in one year, 9.5 × 10¹⁵ m.
13
Spectrum
  • Range of colours in white light.
14
Galactic redshift
  • Shift of galaxy spectral lines to longer wavelength due to recession.
15
Nuclear fusion
  • Joining of light nuclei to form a heavier nucleus, releasing energy.
16
Background radiation
  • Radiation that is always present in the environment.
17
Universe
  • All of space and everything in it.
18
Redshift
  • Increase in the wavelength of light from a source moving away from the observer.
19
Distance
  • Total length of path travelled, a scalar.
20
Radiation
  • Transfer by electromagnetic waves, requiring no medium
21
Wavelength
  • Distance between a point on one wave and the same point on the next wave
22
Reaction
  • The partner force acting on the other object.
23
Constant
  • Not changing.
24
v = H0d
What the symbols mean: v = recession speed of the galaxy (km s−1) · H0 = Hubble constant (km s−1 Mpc−1) · d = distance (Mpc)

Key terms

TermMeaning
NebulaCloud of gas and dust in which stars form.
ProtostarCollapsing cloud that is heating up before fusion begins.
Red giantExpanded, cooler star formed when hydrogen runs out in a low-mass star.
White dwarfSmall, hot, dense core left by a low-mass star.
SupernovaExplosion of a massive star after fusion stops.
Neutron starDense remnant at the centre of a supernova.
Black holeRegion so dense that light cannot escape.

Avoid these mistakes

1
All stars end as black holes — only the most massive do, and low-mass stars end as white dwarfs.
2
The Sun will explode as a supernova — it will become a red giant, then a white dwarf.
3
A star runs out of fuel and stops at once — it expands into a red giant or supergiant first.
4
Heavy elements form in the main sequence — those heavier than iron form in supernovae.

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