Life Cycle Of Stars

• What is the initial stage of a star's life cycle called?

  Nebula
• What force pulls dust and gas together to form a protostar?

  Gravity
• What happens to a protostar as more particles collide with it?

  It gets bigger and its gravity increases
• What effect does gravity have on the density of a protostar?

  It makes the protostar more dense
• What occurs when the temperature of a protostar rises sufficiently?

  Hydrogen nuclei fuse to form helium nuclei
• What is the process called when hydrogen nuclei fuse together?

  Nuclear fusion
• What keeps the core of a star hot during its main sequence phase?

  Energy released by nuclear fusion
• What is a star in its main sequence phase called?

  Main sequence star
• How long can a main sequence star remain stable?

  Billions of years
• What does the star become after contracting due to gravity?

  A small, hot, dense ball
• What balances the outward pressure from nuclear fusion in a main sequence star?

  Inward pressure from gravity
• What happens when a star runs out of hydrogen?

  Nuclear fusion stops and gravity takes over
• What elements can be formed during the nuclear fusion after hydrogen is exhausted?

  Heavier elements up to iron
• What type of star forms if the initial star is small to medium-sized?

  Red giant
• What type of star forms if the initial star is very large?

  Red supergiant
• What happens to a red giant after a relatively short time?

  It becomes unstable and expels outer layers
• What is the core of a red giant called after it expels its outer layers?

  White dwarf
• What happens to a white dwarf over time?

  It gets cooler and darker
• What do we call a white dwarf when it no longer emits light?

  Black dwarf
• What happens to red supergiants after several cycles of expansion and contraction?

  They explode in a supernova
• What elements are formed during a supernova?

  Elements heavier than iron
• What forms if a very big star condenses after a supernova?

  Neutron star
• What forms if an absolutely massive star collapses after a supernova?

  Black hole
• Why are black holes called "black" holes?

  They pull in light due to density
• What is the life cycle of a star from formation to end stages?

  1. Nebula forms from dust and gas
  2. Gravity forms a protostar
  3. Nuclear fusion begins, forming a main sequence star
  4. Star exhausts hydrogen:

  • Small to medium star becomes red giant
  • Large star becomes red supergiant

  1. Red giant:

  • Expels outer layers, becomes white dwarf
  • Cools to black dwarf

  1. Red supergiant:

  • Explodes in supernova
  • Becomes neutron star or black hole
• What is the final stage of a white dwarf's life cycle?

  Black dwarf
• How does the life cycle of a small to medium star differ from that of a large star?

  Small stars become red giants; large stars become red supergiants
• What is the significance of nuclear fusion in a star's life cycle?

  It powers the star and determines its life stages