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 due to particle collisions?

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

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

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

  Main sequence star
• What balances the outward pressure from nuclear fusion in a main sequence star?

  Inward pressure from gravity
• How long can a main sequence star remain stable?

  Billions of years
• What happens when a star runs out of hydrogen?

  Nuclear fusion stops and gravity takes over
• What does the star become after it contracts due to gravity?

  A small, hot, dense ball
• What elements can be formed during nuclear fusion after hydrogen?

  Heavier elements up to iron
• What type of star forms from a small to medium star after hydrogen is exhausted?

  Red giant
• What type of star forms from a really big star after hydrogen is exhausted?

  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 is a white dwarf that no longer emits light called?

  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 after a supernova if the star was very big?

  Neutron star or 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?

  • Nebula forms from dust and gas
  • Protostar forms under gravity
  • Nuclear fusion begins, forming a main sequence star
  • Star exhausts hydrogen, becoming red giant or red supergiant
  • Red giant becomes white dwarf, then black dwarf
  • Red supergiant explodes as supernova, forming neutron star or black hole
• What is the main sequence phase of a star?

  A stable period of nuclear fusion
• What is the relationship between a star's size and its life cycle outcome?

  Size determines whether it becomes a red giant or supergiant
• How does the life cycle of a small star differ from that of a massive star?

  Small stars become red giants; massive stars become supergiants
• What is the final stage of a white dwarf's life cycle?

  It becomes a black dwarf