4 Chapter 4 – What will happen to the Sun?
OpenStax Astronomy Chapter 21: The Birth of Stars
OpenStax Astronomy Chapter 22: Stars from Adolescence to Old Age
OpenStax Astronomy Chapter 23: The Death of Stars
The Life of a Star
I. Overview: of a
A. Stars when causes clouds of gas to
B. Stars make by
1. Converting hydrogen to in their
C. Eventually, fusion source , no longer Hydrogen
1. Changes the of the star like size and luminosity
D. A star’s depends on its and for fusion
II. vs. stars
A. and have different lifetimes
B. Stars with masses have (hydrogen) for fusion
1. stars: Mass is less than Msun
2. High-mass stars: Mass is than 8 Msun
C. More causes
D. Causes interior and (hydrostatic equilibrium)
E. Causes rate of and
F. Therefore, even with fuel, stars have lifetimes on the Main Sequence
1. Evolve more
2. High-mass star lifetimes: of years
3. Low-mass star lifetimes: of years (Sun about billion years)
Why do high-mass stars have shorter lifetimes? Fill in the blank in the cycle below.
High mass stars have more fuel, so stronger gravity, so higher , so faster fusion to burn through the fuel more quickly.
A. Mass and Luminosity
B. Temperature and Pressure
C. Luminosity
D. Hydrostatic Equilibrium
E. Rate of Convection
Main Sequence Stars
III. (MS) Stars
A. Star on MS for of its lifetime while fusing in core
1. MS lifetime for low-mass stars:
B. Star’s will as it uses
1. Must maintain so doesn’t collapse or explode
2. may change a little to maintain balance
C. Eventually, all in is converted to
1. of star’s interior is still
D. Core is now completely leftover from Hydrogen burning
E. more hydrogen in core, so star on the HR Diagram
Consider the information given below about the lifetime of three main sequence stars:
Star A will be on the MS for 45,000 million years.
Star B will be on the MS for 70 million years.
Star C will be on the MS for 2 million years.
Which of the following is a true statement about these stars?
A. Star A has the greatest mass.
B. Star B has the greatest mass.
C. Star C has the greatest mass.
D. Stars A, B, and C all have approximately the same mass.
Evolution of Low-Mass Stars
IV. the MS and becoming Red Giants – Stars
A. for Fusion: , Hydrogen now takes place in a shell around the Helium ash core
1. fusion in : Helium is enough to
B. begins to over the gas , crushing the Helium core
1. The becomes more massive, and
C. Core is now : electrons are packed together as tightly as will go
1. Held together by electron-degeneracy
2. Degenerate core gets as mass is added from shell burning
D.
1. When the core , its gets
2. Stronger gravity –> higher –> nuclear burning –> more being produced =
V.
A. in and results in:
1. overall of the star, just the core is smaller
2. surface
B. The star is now a red giant:
1. But about
C. diagram: star moves and to the away from the MS onto the
1. A star may take of years to go up the branch as properties
When a star runs out of fuel in its core, the core shrinks. Gravity and pressure increase resulting in faster nuclear burning and .
A. smaller overall size
B. higher surface temperature
C. greater luminosity
D. less energy produced
VI.
A. When and dense enough, of starts in the degenerate ash core
1. Temperature in core about million K
B. Helium fuses to
1. Fusion process is different: not proton-proton chain as before
VII. Stars
A. Fuel source for fusion: fuses to Carbon in the AND still fuses to Helium in a
B. Star gets
1. Weaker gravity and lower
C. Star quickly in luminosity
D. Diagram: Drops and to the (HB)
1. Stays there with constant (horizontal line) for a brief time, about 100 million years
When a red giant suddenly starts burning Helium in its core, that is called .
A. A hydrogen shell
B. A helium bump
C. A hydrogen burn
D. A helium flash
Stars on the Horizontal Branch of the HR diagram, have a constant .
A. Surface Temperature
B. Luminosity
C. Size
D. Mass
VIII. Star (like a Red Giant again)
A. Helium is in the
B. Fuel source for fusion: 2 shells: fusion in an and fusion in an outer
C. fusion in the degenerate
D. Star gets more , , and than it was the first time it was a red giant
E. HR Diagram: Enters the (AGB)
1. and to the from the horizontal branch
F. Star has been a little since left MS, at end of AGB stage loses
1. Because of big size, less at outer layers to hold onto gas
Which type of star has a degenerate Carbon core?
A. Red Giant
B. Horizontal Branch Star
C. AGB Star
D. Main Sequence Star
IX.
A. At end of AGB, star becomes very
B. Gravity onto the of the star, and they are into space
C. Remaining star and core and becomes , up to 100,000 K
1. Sends stellar and radiation out into ejected material
D. Creates a
1. Ultraviolet radiation causes atoms in ejected gas to
2. shapes gas
3. See different based on of view
E. HR Diagram: Moves rapidly from across the HR diagram then
1. Planetary Nebula only lasts about years
2. Then, only the carbon core remains, but it is very (white dwarf)
Death of Low-Mass Stars
X.
A. After planetary nebula is gone, of star called a
B. , but very luminous, and very
C. are in the range of Msun
1. Same mass as , but similar to
2. Very : a per teaspoonful
D. Leftover of star
1. Mostly
2. Supported by electron degeneracy
3. , so down with time
E. HR Diagram: Lower corner, moves and
1. Size stays , but gets cooler and with time
F. stars become white dwarfs
G. Ends up as Dwarf
1. After of years, white dwarf cools so much it longer light
2. only, have not observed black dwarf
3. Universe may not be enough to have black dwarfs because it takes too long for white dwarf to cool
Which of the following is the correct order for the stages of evolution of the Sun?
A. Main sequence, white dwarf, planetary nebula, red giant
B. Main sequence, red giant, white dwarf, planetary nebula
C. Main sequence, red giant, planetary nebula, white dwarf
D. Main sequence, planetary nebula, red giant, white dwarf
When will the Sun leave the main sequence?
A. When Hydrogen is used up in the Core
B. When ALL the Sun’s Hydrogen becomes Helium
C. When Carbon fusion begins
D. When it becomes an AGB star
Evolution of Binary Stars
XI. Stars
A. stars are in or systems
1. Stars orbit one another
B. In a of stars, the star with evolves
1. Example: If have 1 Msun star and 2 Msun star – Msun is more massive and becomes before 1 Msun star becomes a
2. Lifetime of 1 Msun star than as long as 2 Msun star
C. : When more massive star is a Red Giant and smaller one is still on MS, material from the to the smaller due to
D. More star then evolves to become a
E. When the (less massive) star becomes a later, it can material onto the
XII.
A. gas collects on the due to mass transfer from companion red giant
B. starts and burns through thin layer of Hydrogen, then
C. Called a : White dwarf gets much
1. Last for a few
2. times than the Sun
D. When burned through all the , it goes back to a normal
1. Can repeat process and be nova times
a. Usually takes of years, but some only a few decades
XIII.
A. The for a white dwarf is Msun
1. Called the Chandrasekhar
B. If pushed this limit by mass transfer, White Dwarf will
C. carbon of White Dwarf results in a
D. Explosion is briefly as luminous as Suns
1. Brighter than a whole , so can be seen at large (in other galaxies)
2. Creates new like and nickel in explosion
3. May occur in a century per galaxy
E. The White Dwarf is completely , left
Imagine a binary system with one star like the Sun and one star a little more massive than the Sun.
Which of the following states is NOT possible later on?
A. Two white dwarf stars
B. A white dwarf and a main-sequence star
C. Two AGB stars
D. A white dwarf and a red giant
Tutorial Activity – Low-Mass Stellar Evolution
“Elementary Astronomy Worksheet Handout 19: Life Cycles of Stars” (modified by Kaisa E. Young) by Catherine Whiting via OER Commons, licensed under CC BY 4.0, https://oercommons.org/courses/elementary-astronomy-worksheets
1. Why do high-mass stars live very short lives if they have so much more ‘fuel’ to burn?
2. Would a red main sequence star live a long or short life compared to the sun?
3. What event triggers the beginning of the death of all stars?
4. Put the following in order of the evolution of a low-mass star. What is the name of each stage?
- A: Fusing hydrogen into helium in a shell around its core and in its core helium is fusing into carbon.
- B: Composed primarily of Carbon and has no nuclear reactions ongoing in its core.
- C: Fusing hydrogen into helium in its core.
5. What will remain of the Sun after it dies?
6. Create a flowchart or draw an HR diagram showing all the stages of low-mass star from main sequence to white dwarf.
7. Create a flowchart or describe how novas and Type Ia supernova can happen.
