ISP 205 Exam 3 2024/2025 Exam
Questions and Answers | A+ Score
Assured
Describe how gravitational contraction eventually triggers nuclear fusion in
a star-forming cloud. - 🧠ANSWER ✔✔-Gravity makes the cloud
shrink/fragment, the core heats up as it shrinks, then fusion begins once its
hot enough to stop it from shrinking more
-Fusion begins supplying energy in the core once it heats up enough
(contracts because core generates less energy than the surface radiates
into space)
Explain why contracting gas clouds with masses less than 0.08 MSun fail to
achieve energy balance. - 🧠ANSWER ✔✔-Degeneracy pressure stops the
contraction of the core of brown dwarfs before it gets hot enough for fusion
to start
-Degeneracy Pressure: particles like electrons are prevented from
occupying the same state in a small region of space
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STATEMENT. ALL RIGHTS RESERVED
,Predict how the central temperature of a star changes after fusion exhausts
the fuel in its core. - 🧠ANSWER ✔✔-The core cools off and shrinks while
the rest of the star expands. The outer layers expand, and the star
becomes a subgiant and then a red giant.
-heats up again as hydrogen fuses in the shell around the core to become
Red giant
Explain how H-R diagrams of star clusters support our models of how stars
change near the ends of their lives. - 🧠ANSWER ✔✔They contain stars of
the same age but at different life stages as luminosity/surface temperature
change
Explain why fusion in stars of greater mass can produce elements with
more protons in their nuclei. - 🧠ANSWER ✔✔The cores reach much higher
temperatures, so heavier elements can combine multiple protons at a time
for fusion rather than just 2 hydrogen
Describe what ultimately happens to a star with an iron core. - 🧠ANSWER
✔✔-Iron cannot release energy either by fission or fusion, so it has no way
to generate the energy needed to counteract gravity so it initiates a
supernova.
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STATEMENT. ALL RIGHTS RESERVED
, -The sudden collapse of an iron core into a compact ball of neutrons means
degeneracy pressure cannot resist gravity any longer so it causes a
supernova explosion
Predict the life history of a star with a given mass. - 🧠ANSWER ✔✔-Low
mass (11.5 Billion years): Protostar, main sequence, subgiant, red giant (H
to He then He to C), Double shell fusion, planetary nebula, white dwarf
-High Mass (> 8 * Sun)(6 million years): Protostar, Blue main sequence,
red supergiant (H to He then He to C), multiple shell fusion, supernova,
neutron star
-Mass determines whether the star's core will ever be compressed enough
to fuse heavy elements
Explain why stars form most easily in interstellar gas clouds that are both
cold and dense. - 🧠ANSWER ✔✔-Gravity can overcome thermal pressure
in the cold and higher density means better chance for stars to form
because more atoms are present to combine
-This cloud has lower thermal pressure (due to the low temperature) and
stronger gravity (due to the high density), giving gravity the upper hand.
COPYRIGHT©JOSHCLAY 2025/2026. YEAR PUBLISHED 2025. COMPANY REGISTRATION NUMBER: 619652435. TERMS OF USE. PRIVACY
3
STATEMENT. ALL RIGHTS RESERVED
Questions and Answers | A+ Score
Assured
Describe how gravitational contraction eventually triggers nuclear fusion in
a star-forming cloud. - 🧠ANSWER ✔✔-Gravity makes the cloud
shrink/fragment, the core heats up as it shrinks, then fusion begins once its
hot enough to stop it from shrinking more
-Fusion begins supplying energy in the core once it heats up enough
(contracts because core generates less energy than the surface radiates
into space)
Explain why contracting gas clouds with masses less than 0.08 MSun fail to
achieve energy balance. - 🧠ANSWER ✔✔-Degeneracy pressure stops the
contraction of the core of brown dwarfs before it gets hot enough for fusion
to start
-Degeneracy Pressure: particles like electrons are prevented from
occupying the same state in a small region of space
COPYRIGHT©JOSHCLAY 2025/2026. YEAR PUBLISHED 2025. COMPANY REGISTRATION NUMBER: 619652435. TERMS OF USE. PRIVACY
1
STATEMENT. ALL RIGHTS RESERVED
,Predict how the central temperature of a star changes after fusion exhausts
the fuel in its core. - 🧠ANSWER ✔✔-The core cools off and shrinks while
the rest of the star expands. The outer layers expand, and the star
becomes a subgiant and then a red giant.
-heats up again as hydrogen fuses in the shell around the core to become
Red giant
Explain how H-R diagrams of star clusters support our models of how stars
change near the ends of their lives. - 🧠ANSWER ✔✔They contain stars of
the same age but at different life stages as luminosity/surface temperature
change
Explain why fusion in stars of greater mass can produce elements with
more protons in their nuclei. - 🧠ANSWER ✔✔The cores reach much higher
temperatures, so heavier elements can combine multiple protons at a time
for fusion rather than just 2 hydrogen
Describe what ultimately happens to a star with an iron core. - 🧠ANSWER
✔✔-Iron cannot release energy either by fission or fusion, so it has no way
to generate the energy needed to counteract gravity so it initiates a
supernova.
COPYRIGHT©JOSHCLAY 2025/2026. YEAR PUBLISHED 2025. COMPANY REGISTRATION NUMBER: 619652435. TERMS OF USE. PRIVACY
2
STATEMENT. ALL RIGHTS RESERVED
, -The sudden collapse of an iron core into a compact ball of neutrons means
degeneracy pressure cannot resist gravity any longer so it causes a
supernova explosion
Predict the life history of a star with a given mass. - 🧠ANSWER ✔✔-Low
mass (11.5 Billion years): Protostar, main sequence, subgiant, red giant (H
to He then He to C), Double shell fusion, planetary nebula, white dwarf
-High Mass (> 8 * Sun)(6 million years): Protostar, Blue main sequence,
red supergiant (H to He then He to C), multiple shell fusion, supernova,
neutron star
-Mass determines whether the star's core will ever be compressed enough
to fuse heavy elements
Explain why stars form most easily in interstellar gas clouds that are both
cold and dense. - 🧠ANSWER ✔✔-Gravity can overcome thermal pressure
in the cold and higher density means better chance for stars to form
because more atoms are present to combine
-This cloud has lower thermal pressure (due to the low temperature) and
stronger gravity (due to the high density), giving gravity the upper hand.
COPYRIGHT©JOSHCLAY 2025/2026. YEAR PUBLISHED 2025. COMPANY REGISTRATION NUMBER: 619652435. TERMS OF USE. PRIVACY
3
STATEMENT. ALL RIGHTS RESERVED
