Astronomy: Stellar Evolution Practice Flashcards

Flashcards reviewing stellar evolution stages, nuclear fusion cycles, HR diagram transitions, spectral classifications, and event parameters.

What primary factor determines the life cycle and eventual fate of a star?

A star's fate largely depends on its initial mass.

What is the dominant inward force operating within a star?

Gravity, which pulls the mass of the star toward its center.

What is the primary outward force that counteracts gravity in a star?

Thermal and radiation pressure, generated by extreme heat and photons from nuclear fusion.

What are molecular clouds and what role do they play in star formation?

Vast, cold, and dense regions in space composed of gas and dust where molecules form, providing the raw materials and conditions necessary for star and planet formation.

How is heat generated during the gravitational collapse of a protostellar core?

Heat is generated due to the conversion of gravitational potential energy into thermal energy.

At what critical core temperature does hydrogen fusion begin in a protostar?

Around $10\text{ million K}$.

How is accretion defined in astrophysics?

The accumulation of particles into a massive object by gravitationally attracting more matter, typically gaseous matter, into an accretion disk.

What defines a main sequence star?

A star that is actively fusing hydrogen into helium in its core, maintaining a stable balance between inward gravity and outward pressure from nuclear fusion.

What is the mass range for Red Giants relative to the Sun?

Half to $10\times$ the mass of the Sun.

What is the mass range for Red Supergiants relative to the Sun?

$10$ to $25\times$ the mass of the Sun.

Which fusion cycle is used by stars heavier than about $1.3$ solar masses to fuse hydrogen?

The CNO Cycle, which uses carbon, nitrogen, and oxygen as catalysts.

At what core temperature does the Triple-Alpha Process begin, and what does it fuse?

At a core temperature of $100\,\text{M K}$, where helium fuses into carbon.

What elements are produced when carbon fuses with helium in the Alpha Process?

Oxygen, neon, and magnesium.

What properties of stars are classified on the Hertzsprung-Russell (H-R) diagram scatter plot?

Luminosity (brightness) and temperature.

What happens to low- to intermediate-mass stars on the H-R diagram during the Red Giant Branch (RGB) stage?

After exhausting hydrogen fuel in their cores, they expand and cool, moving up and to the right on the H-R diagram.

What nuclear fusion reactions take place during the Horizontal Branch stage of a star?

Helium is fused into carbon in the core, while hydrogen is burned in a shell surrounding the core.

What solar mass range populates the Asymptotic Giant Branch (AGB) stage?

Roughly $0.5$ to $8$ solar masses ($0.5\text{ to }8\,M_\odot$).

What effective temperature and mass range characterize Class O main-sequence stars?

An effective temperature of $\ge 30,000\,\text{K}$ and a mass of $\ge 16\,M_\odot$.

What fraction of all main-sequence stars are Class M stars?

$76.45\%$.

At what specific event does a star leave the main sequence?

When it runs out of hydrogen fuel in its core.

What will a main-sequence star of $2\,M_\odot$ eventually evolve into?

A Red giant.