8.1.2 Life Cycle of a Star

• The core of a star is the region where nuclear fusion occurs.
• Stars form from a large cloud of gas and dust called a nebula.
• What process sustains a star's luminosity during its main sequence stage?

  Hydrogen fusion
• Match the evolutionary stages of low-mass and high-mass stars after the main sequence:

  Low-Mass Stars ↔️ Red Giant

  High-Mass Stars ↔️ Supergiant
• Steps in the formation of a star from a nebula

  1️⃣ A nebula collapses under its own gravitational attraction

  2️⃣ The center heats up, forming a protostar

  3️⃣ Nuclear fusion is triggered in the core

  4️⃣ The star stabilizes into a main-sequence star
• Match the star stage with its primary process:

  Main sequence ↔️ Fusing hydrogen into helium

  Red giant ↔️ Helium fusion into carbon and oxygen

  Supernova ↔️ Collapse of a high-mass star
• Lower-mass stars have longer lifespans because they burn their fuel more slowly
• Supergiants can fuse elements up to iron in their cores.


  True
• Match the star type with its description:

  White dwarf ↔️ Dense remnant of a low-mass star

  Neutron star ↔️ Extremely dense star formed in a supernova
• The singularity in a black hole is a point of infinite density
• What is a star primarily composed of?

  Plasma
• What is the main process occurring in the core of a star?

  Nuclear fusion
• Steps in the formation of a star from a nebula:

  1️⃣ Nebula collapses under gravity

  2️⃣ Protostar forms at the center

  3️⃣ Nuclear fusion begins in the core

  4️⃣ Main-sequence star stabilizes
• Lower-mass stars have shorter main sequence lifespans than higher-mass stars.

  False
• A high-mass star can end its life as a supernova, leading to a neutron star or a black hole.


  True
• A star becomes stable as a main-sequence star after nuclear fusion releases vast amounts of energy
• The duration of the main sequence stage depends on the star's mass.


  True
• Match the star mass with its evolutionary stages:

  Low-mass star ↔️ Red giant, then white dwarf

  High-mass star ↔️ Supergiant, then supernova
• Hydrogen fusion releases more energy per reaction than helium fusion.


  True
• Neutron stars are denser than black holes.

  False
• The photosphere is the visible outer layer of a star.

  True
• A protostar is the initial stage in a star's formation.


  True
• The main sequence lifespan of a star depends on its mass.
• What is the final form of a low-mass star?

  White dwarf
• Nuclear fusion in a protostar converts hydrogen into helium.


  True
• During the main sequence stage, a star is sustained by the energy released from fusing hydrogen into helium
• Stars are categorized as low-mass if they are up to 8 solar masses.


  True
• The helium flash in a red giant converts helium into carbon
• Steps in the formation of a black hole

  1️⃣ A high-mass star undergoes a supernova explosion

  2️⃣ The remaining core collapses under gravity

  3️⃣ A black hole with infinite density is formed