GCSE Physics (AQA)

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White & Black Dwarves

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Space physics Solar system; stability of orbital motions; satellites

White & Black Dwarves

4:03 Life Cycle of a Star
Spec 4.8.1.2
Previous Red Giants & Supergiants Next Neutron Star & Black Holes
  • A low mass star evolves into a red giant through helium fusion reactions.
  • Initially, a star is in its main sequence, stabilized by hydrogen fusion into helium.
  • Prior to becoming a main sequence star, it exists as a proto star, formed from gas and dust due to gravity.
  • The Sun is an example of a low mass star.
  • As a low mass star exhausts its hydrogen, it collapses and heats, enabling helium fusion.
  • This process causes the star to expand into a red giant.
  • After depleting its helium, the red giant collapses into a white dwarf.
  • Helium fusion in a red giant creates outward pressure balancing the inward gravitational pull.
  • Once helium is exhausted, the star's outer layers collapse, leaving a white dwarf about the size of Earth.
  • The Sun is expected to become a white dwarf in about 8 billion years.
  • Larger stars become red supergiants and follow a different evolutionary path, not becoming white dwarfs.
  • A white dwarf has no internal fusion and glows due to residual thermal energy from its red giant phase.
  • The surface temperature of a white dwarf can exceed 50,000 degrees Celsius.
  • Eventually, a white dwarf cools and darkens, becoming a black dwarf, marking the end of its life cycle.
  • Black dwarfs emit no energy or light, consisting only of particles held together by gravity, with all previous energy dissipated.

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