5.5.1 Stellar Evolution

• During the collapse stage of star formation, gravity increases the density and temperature
• Main sequence stars are in hydrostatic equilibrium
• Match the characteristics with the type of star

  Pre-Main Sequence Star ↔️ Kelvin-Helmholtz contraction

  Main Sequence Star ↔️ Nuclear fusion
• Stages in the formation of a star within a molecular cloud

  1️⃣ Collapse

  2️⃣ Protostar Formation

  3️⃣ Nuclear Fusion
• What type of energy source powers a pre-main sequence star?

  Kelvin-Helmholtz contraction
• Main sequence stars produce energy through the fusion of hydrogen into helium in their core.


  True
• What is the most common and stable stage of a star's life cycle?

  Main sequence
• Stages in the post-main sequence evolution of low mass stars

  1️⃣ Red Giant

  2️⃣ Planetary Nebula

  3️⃣ White Dwarf
• A pre-main sequence star has not yet begun nuclear fusion
• Red giants begin fusing helium in their core as hydrogen is depleted.
• In the core of a red giant, hydrogen is depleted, and the core begins to contract
• What drives the expansion of a red giant's outer layers?

  Hydrogen depletion
• A white dwarf eventually collapses into a black hole

  False
• Match the stage of stellar evolution with the corresponding event:

  Red Giant ↔️ Core contracts as hydrogen is depleted

  Supernova ↔️ Catastrophic core collapse

  White Dwarf ↔️ Dense, cooling core

  Planetary Nebula ↔️ Outer layers are ejected
• What triggers a supernova explosion in a high mass star?

  Core collapse
• As a star's core runs out of hydrogen, it begins to contract under its own gravity
• What is the composition of neutron stars?

  Neutron-degenerate matter
• Nuclear fusion marks the birth of a main sequence star when hydrogen is fused into helium.

  True
• A pre-main sequence star's luminosity is derived from nuclear reactions.

  False
• Pre-main sequence stars have core temperatures high enough for nuclear fusion.

  False
• Main sequence stars maintain hydrostatic equilibrium due to nuclear fusion.


  True
• Stars form within giant molecular clouds
• Main sequence stars have core temperatures hot enough for nuclear fusion of hydrogen into helium
• The luminosity of a red giant is lower than that of a main sequence star

  False
• Order the stages in the post-main sequence evolution of low mass stars:

  1️⃣ Red Giant

  2️⃣ Planetary Nebula

  3️⃣ White Dwarf
• How does the post-main sequence evolution of high mass stars differ from that of low mass stars?

  High mass stars undergo supernovae
• A black hole can form from the remnant of a high mass star


  True
• Order the stages in the process leading to a supernova explosion:

  1️⃣ Core Collapse

  2️⃣ Fusion Reactions

  3️⃣ Supernova Explosion

  4️⃣ Remnant Formation
• What happens to the outer layers of a star during a supernova explosion?

  They are blown off
• The gravity of a neutron star is strong enough to trap light

  False
• The transition of a star into the red giant phase is driven by the depletion of hydrogen fuel in its core.


  True
• During protostar formation, heat is generated by Kelvin-Helmholtz contraction
• The higher luminosity of main sequence stars is derived from nuclear reactions in their core.

  True
• What happens to the core of a star as it transitions into a red giant phase?

  It contracts
• What is the primary energy source of a red giant?

  Helium fusion
• When a low mass star ejects its outer layers, it forms a colorful, glowing shell called a planetary nebula
• A high mass star ends its life in a violent explosion called a supernova
• Supernovae are crucial for distributing heavy elements throughout the cosmos

  True