8.1.2 Life Cycle of a Star

• What is a nebula made of?

  Gas and dust
• Stages of nebula formation

  1️⃣ Gravitational Collapse

  2️⃣ Protostar Formation

  3️⃣ Accretion Disk

  4️⃣ Star and Planetary System
• Nebula formation is the first step in a star's life cycle.


  True
• Nebulae form from the gravitational collapse of giant molecular clouds
• What forms at the center of a collapsing nebula?

  Protostar
• What force pulls material together in a nebula to form a protostar?

  Gravity
• Stages of protostar formation

  1️⃣ Gravitational Collapse

  2️⃣ Accretion Disk Formation

  3️⃣ Heating and Ignition
• A protostar becomes a young star once nuclear fusion begins.


  True
• In a main sequence star, outward radiation pressure balances inward gravity
• How long do main sequence stars burn hydrogen?

  Millions to billions of years
• What type of disk forms around a protostar?

  Accretion disk
• Nuclear fusion in a protostar begins as the core compresses and heats up.


  True
• Match the stage or process with its description in a main sequence star:

  Nuclear Fusion ↔️ Hydrogen atoms fuse to form helium

  Equilibrium ↔️ Outward pressure balances inward gravity

  Steady Burning ↔️ Stars burn hydrogen for billions of years
• The Red Giant Phase occurs after the Main Sequence phase.
• Red giants expand and cool due to helium fusion in their core.


  True
• What temperature is required for helium fusion to begin in a star's core?

  100 million Kelvin
• Stages in the life cycle of a star in order:

  1️⃣ Nebula

  2️⃣ Protostar

  3️⃣ Main Sequence Star

  4️⃣ Red Giant
• What temperature is typically required for helium fusion to occur?

  100 million Kelvin
• Helium fusion releases significant energy but less than hydrogen fusion.
• Stages of nebula formation

  1️⃣ Gravitational Collapse

  2️⃣ Protostar Formation

  3️⃣ Accretion Disk

  4️⃣ Star and Planetary System
• Stages of protostar formation

  1️⃣ Gravitational Collapse

  2️⃣ Accretion Disk Formation

  3️⃣ Heating and Ignition
• In a main sequence star, outward radiation pressure balances inward gravity.
• A red giant's luminosity is moderate compared to the Sun.

  False
• What marks the end of the red giant phase in a star's life cycle?

  Shedding outer layers
• Supernovae can occur in massive stars as a result of core collapse during helium fusion.


  True
• A supernova is a cataclysmic explosion marking the end of a massive star's life cycle
• What type of end product forms if a star's initial mass is between 8 to 20 solar masses after a supernova?

  Neutron star
• What is the defining feature of a black hole?

  Singularity with event horizon
• At what process does the core collapse of a neutron star stop?

  Neutron degeneracy
• Black holes are invisible but can be detected by their gravitational effects on surrounding matter.


  True
• What is the role of nebulae in the life cycle of a star?

  First step
• What type of star does a protostar become once nuclear fusion starts in its core?

  Young star
• What forces are balanced in a main sequence star to maintain equilibrium?

  Gravity and radiation pressure
• The red giant phase occurs when a star's core runs out of hydrogen
• What temperature is required for helium fusion to begin in a star's core?

  100 million Kelvin
• After leaving the Main Sequence, a star becomes a red giant
• Arrange the life cycle stages of a star after the Main Sequence in the correct order.

  1️⃣ Red Giant

  2️⃣ Helium Fusion

  3️⃣ Core Collapse

  4️⃣ Supernova (if massive)

  5️⃣ Neutron Star or Black Hole (if massive)
• Match the fusion process with its requirements and outcomes:

  Hydrogen Fusion ↔️ 4-20 million Kelvin, Helium

  Helium Fusion ↔️ 100 million Kelvin, Carbon and Oxygen
• A supernova marks the end of a massive star's life cycle
• What is the mass range required for a star to become a neutron star after a supernova?

  8-20 solar masses