life cycle of a star

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

  Nuclear fusion
• What occurs when the temperature inside a protostar rises due to particle collisions?

  Hydrogen nuclei start to fuse into helium
• What type of star is formed when nuclear fusion begins?

  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 fuel?

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

  A hot dense core
• What is formed during nuclear fusion after the star has contracted?

  A heavier element, including 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 is a black dwarf?

  A white dwarf that no longer emits light
• 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?

  A black hole
• What forms after a supernova if the star was only very big?

  A neutron star
• Why are black holes called "black" holes?

  They pull in light due to their density
• What are the main stages in the life cycle of a star?

  1. Nebula forms a protostar
  2. Nuclear fusion begins, forming a main sequence star
  3. Star exhausts hydrogen and becomes either:

  • Red giant (small to medium stars)
  • Red supergiant (large stars)

  1. Red giant becomes a white dwarf, then a black dwarf
  2. Red supergiant explodes in a supernova, forming:

  • Neutron star (if very big)
  • Black hole (if truly massive)
• What are the differences between a red giant and a red supergiant?

  • Red giant:
  • Forms from small to medium stars
  • Expels outer layers to become a white dwarf
  • Red supergiant:
  • Forms from very large stars
  • Explodes in a supernova, forming neutron stars or black holes
• What is the final fate of a white dwarf?

  • It cools and becomes a black dwarf
• What is the significance of nuclear fusion in a star's life cycle?

  • It provides energy to keep the star hot
  • It allows the star to maintain balance against gravity