Ast Final Flashcards
I) Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ
mass they are formed with
A starS luminosity is the
total amount of energy that the star radiates each second.
3) If the distance between us and a star is doubled, with everything else remaining the same, its luminosity
remains the same, but its apparent brightness is decreased by a factor of four.
You mesure the parallax angle for a star to be O.I arcseconds. The distance to this star is
10 parsecs.
You mesure the parallax angle for a star to be 0.5 arcseconds. The distance to this star is
2 parsecs.
The spectral sequence sorts stars according to
surtace temperar.
The stellar spectral sequence, in order of decreasing temperature, iS
OBAFGKM.
8) Which of the following statements about spectral types of stars is true?
All of the above are true.
Which of the following terms is given to a pair of stars that appear to change position in the sky, indicating
that they are orbiting one another?
visual binary
Which of the following best describes the axes of a Hertzsprung-Russell (H-R) diagram?
surtace temperature on the horizontal axis and luminosity on the vertical axis
11) On a Hertzsprung-Russell diagram, where would you find stars that are cool and dim?
lower right
On a Hertzsprung-Russell diagram, where would you find stars that are cool and luminous?
upper right
13) On a Hertzsprung-Russell diagram, where would you find stars that have the largest radii?
Upper right
14) On a Hertzsprung-Russell diagram, where on the main sequence would you find stars that have the greatest mass
C) upper left
On a Hertzsprung-Russell diagram, where would you find red giant stars?
A) upper right
On a Hertzsprung-Russell diagram, where would you find white dwarts?
lower left
On the main sequence, stars obtain their energy
by converting hydrogen to helium.
Which of the following luminosity classes refers to stars on the main sequence?
V
Which of the following comparisons between low-mass stars and high-mass main-sequence stars 1s true?
Low-mass stars are cooler and less luminous than high-mass stars
A main-sequence star’s luminosity can directly inform us of
the rate at which it converts hydrogen to helium
On an H-R diagram, stellar radii
increase diagonally from the lower left to the upper right
How is the lifetime of a star related to its mass?
More massive stars live much shorter lives than less massive stars
Each choice below lists a spectral type and luminosity class for a star. Which one is a red supergiant?
spectral type M2, luminosity class I
What is the common trait of all main-sequence stars?
They generate energy through hydrogen fusion in their core.
Which star is the hottest star?
O
Which main-sequence star will have the shortest lifetime?
O
Which main-sequence star has the lowest mass?
M
An O-star has a hotter surface temperature than the Sun. Therefore, compared to the Sun,
its emission peaks in the blue part of the spectrum.
What is the approximate chemical composition (by mass) with which all stars are born?
Three quarters hydrogen, one quarter helium, no more than 2% heavier elements
The total amount of power (in watts, for example) that a star radiates into space is called its
Lumosinity
According to the inverse square law of light, how will the apparent brightness of an object change if its
distance to us triples?
Its apparent brightness will decrease by a factor of 9.
Assuming that we can mesure the apparent brightness of a star, what does the inverse square law for light
allow us to do?
calculate the star’s luminosity if we know its distance, or calculate its distance if we know its luminosity
If Star A is closer to us than Star B, then Star A’s parallax angle is
larger than that of Star B
Star A has an apparent magnitude of3, and Star B has an apparent magnitude of S. Which star is brighter in our sky
Star A
Our Sun is a star of spectral type
G
36) Which of the following terms is given to a pair of stars that we can determine are orbiting each other only by measuring periodic Doppler shifts
spectroscopic binary
What can we infer, at least roughly, from a star’s luminosity class?
its size (radius)
What is a white dwarf?
the remains of a star that ran out of fuel for nuclear fusion
All stars are born with the same basic composition, yet stars can look quite different from one another.
Which two factors primarily determine the characteristics of a star?
its mass and its stage of life
Sirius is a star with spectral type A and Rigel is a star with spectral type B. What can we conclude?
Rigel has a higher surface temperature than Sirius.
The sketch above shows groups of stars on the H-R diagram, labeled (a) through (e); note that (a) represents
the entire main sequence while (c) and (d) represent only small parts of the main sequence. Which group represents starts that are cool and dim
D
The sketch above shows groups of stars on the H-R diagram, labeled (a) through (e); note that (a) represents
the entire main sequence while (c) and (d) represent only small parts of the main sequence. Which group
represents stars of the largest radit?
E
Mi
H
The sketch above shows groups of stars on the H-R diagram, labeled (a) through (e); note that (a) represents
the entre main sequence while (C) and (d) represent only small parts of the main sequence. Which group start with largest radii
E
The sketch above shows groups of stars on the H-R diagram, labeled (a) through (e); note that (a) represents
the entire main sequence while (c) and (d) represent only small parts of the main sequence. Which group
represents stars that are extremely bright and emit most of their radiation as ultraviolet light?
C
The sketch above shows groups of stars on the H-R diagram, labeled (a) through (e); note that (a) represents
the entire main sequence while (c) and (d) represent only small parts of the main sequence. Which group
represents stars with the longest main-sequence lifetimes?
D
The sketch above shows groups of stars on the H-R diagram, labeled (a) through (e); note that (a) represents
the entire main sequence while (c) and (d) represent only small parts of the main sequence. Which group
represents stars fusing hvdrogen in their cores
A
The sketch above shows groups of stars on the H-R diagram, labeled (a) through (e); note that (a) represents
the entre main sequence while (c) and (d) represent only small parts of the main sequence. Which group
represents stars that have no ongoing nuclear fusion?
B
1) wnat eventually nalts the gravitational collapse of an interstellar gas cloud that forms an object that is
massive enough to become a star!
the
central object becoming hot enough to sustain nuclear tusion 1n 1ts core
What type of star is our Sun?
A low mass star
No stars are expected with masses greater than 150 times our Sun because
C) they would generate so much power that they would blow themselves apart.
What eventually halts the gravitational collapse of an interstellar gas cloud that forms an object that is not
massive enough to become a star!
the crowding of electrons in the core
What can we learn about a star from a life track on an H-R diagram?
what surface temperature and luminosity it will have at each stage of its life
As a solar mass protostar moves on to the main sequence.
ts surface temperature increases and its luminositv decreases.
When does a star become a main-sequence star!
C) when the rate of hydrogen fusion in the star’s core is high enough to sustain gravitational equilibrium
What percentage of a star s total litetime 1s spent on the main sequence?
90%
What happens when a star like the sun exhausts its core hydrogen supply?
Its core contracts, but its outer layers expand and the star becomes bigger and brighter.
Compared to the star it evolved trom, a red giant is
cooler and brighter.
11) What is a planetary nebula?
the expanding shell of gas that is no longer gravitationally bound to the remnant of a low-mass star
What happens to the core of a star after it ejects a planetary nebula?
It becomes a white dwarf.
Which of the following sequences correctly describes the stages of life for a low-mass star?
protostar, main-sequence, red giant, White dwarl
Compared to the star it evolved from, a white dwarf is
hotter and dimmer.
Why does stellar main-sequence lifetime decrease with increasing stellar mass?
Higher core temperatures cause fusion to proceed much more rapidly.
What happens when the gravity of a massive star is able to overcome neutron degeneracy pressure?
The core contracts and becomes a black hole.
What types of stars end their lives with supernovae?
stars that are at least several times the mass of the Sun
After a supernova event occurring in a high-mass star, what is left behind?
either a neutron star or a black hole
Which method of energy generation is used by the Sun today?
H fusion by the proton-proton chain
Which one provided the energy that made the Sun hot in the first place?
gravitational contraction
Which method of energy generation provides the source of energy for a protostar?
gravitational contraction
Which process leads to the production of carbon?
helium fusion
When a 1-solar-mass star stabilizes as a giant for about a billion years, which method of energy generation
occurs in its central core?
helium tusion
Which one is used by a main-sequence star of spectral type B2?
H fusion by the CNO cycle
Which method of energy generation provides the source of energy for a 10M Sun main-sequence star?
H fusion by the CNO cycle
Which type of star spends the shortest time as a main sequence star?
O star
Identify the correct sequence of life events for a high mass star.
main sequence, red supergiant, supernova, neutron star
Which of the following properties describes a low-mass star?
has longer lifetimes than high mass stars
29) What will happen in the Sun immediately after it has exhausted its supply of hydrogen in its core?
The Sun will turn into a white dwarf and cool off forever.
Which element is the dead end for cores of the most massive stars?
iron
Why don’t low-mass stars have the CNO cycle occurring in their cores?
Their core temperatures are too low.
Why is a 1 solar-mass red giant more luminous than a 1 solar-mass main sequence star?
Fusion reactions are producing energy at a greater rate in the red giant.
33) Which is more common: a star blows up as a supernova, or a star forms a planetary nebula/white dwarf system
Planetarv nebula tormation is more common
Why don’t low-mass stars have the CNO cycle occurring in their cores?
Their core temperatures are too low.
32) Why is a l solar-mass red giant more luminous than a 1 solar-mass main sequence star?
Fusion reactions are producing energy at a greater rate in the red giant
Which is more common: a star blows up as a supernova, or a star forms a planetary nebula/white dwarf
system?
Planetary nebula formation is more common.
white dwarf is
the exposed core of a dead star, supported by electron degeneracy pressure
Why is there an upper limit to the mass of a white dwarf?
B) The more massive the white dwarf, the greater the degeneracy pressure and the faster the speeds of its electrons. Near 1.4 solar masses, the speeds of the electrons approach the speed of light, and no more mass can
3) Suppose a white dwarf is gaining mass because of accretion from a binary companion. What happens if its mass reaches the 1.4 solar mass limit?
The white dwarf (which is made mostly of carbon) suddenly detonates carbon fusion and this creates a white dwarf supernova explosion.
Which of the following is closest in size (radius) to a white dwarf?
the Earth
Which of the following is closest in size (radius) to a neutron star?
A city
Observationally, how can we tell the difference between a white-dwarf supernova and a massive-star supernova?
C) The spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white- dwarf supernova does not.
After a massive-star supernova, what is left behind?
either a neutron star or a black hole
8) From a theoretical standpoint, what is a pulsa
a rapidly rotating neutron star
How does a black hole form from a massive star?
During a supernova, if a star is massive enough for its gravity to overcome neutron degeneracy pressure in the core, the core will collapse to a black hole.
A 10 solar mass main sequence star will produce which of the following remnants?
neutron star
You are studying a mystery companion to an evolved star, with mass transfer happening. Which of the following properties suggests that the companion is definitely a black hole?
The mystery companion has a mass of over 3 solar masses.
Rank the following 4 items in order of increasing density (low to high).
main-sequence star, white dwarf, neutron star, black hole singularity
The Crab Pulsar is pulsing in visible light 30 times per second. Why? A)
It rotates 30 times per second
Order these objects by size (radius) from smallest to larges
D) 3 solar mass black hole, 3 solar mass neutron star, 1 solar mass white dwarf, 0.5 solar mass white dwarfs
Order the following objects in increasing size (radius):
neutron star, white dwarf, Jupiter, Sun
A white dwarf supernova leaves behind
nothing
A typical white dwarf is
as massive as the Sun but only about as large in size as Earth
about the mass of our Sun
about 1.4 times the mass of our Sun
What is an accretion disk?
A disk of hot gas swirling rapidly around a white dwarf, neutron star, or black hole
According to our modern understanding, what is a nova?
an explosion on the surface of a white dwarf in a close binary system
Suppose that a white dwarf is gaining mass through accretion in a binary system. What happens if the mass someday reaches the 1.4 solar mass limit?
The white dwarf will explode completely as a white dwarf supernova
A neutron star is
A) the remains of a star that died in a massive star supernova (if no black hole were created)
Pulsars are thought to be __
B) rapidly rotating neutron stars
What is the basic definition of a black hole?
A) an object with gravity so strong that not even light can escape
Based on current understanding, the minimum mass of a black hole that forms during a massive star supernova is roughly __
3 solar masses
What do we mean by the event horizon of a black hole?
It is the point beyond which neither light nor anything else can escape.
27) Imagine that our Sun were magically and suddenly replaced by a black hole of the same mass (1 solar mass). What would happen to Earth in its orbit?
D) Nothing; Earth’s orbit would remain the same.
The Schwarzschild radius of a black hole depends on ______
only the mass of the black hole
The more massive a white dwarf, the _____
A) smaller its radius
30) Which of the following best describes why a white dwarf cannot have a mass greater than the 1.4-solar- mass limit
Electron degeneracy pressure depends on the speeds of electrons, which approach the speed of light as a white dwarf’s mass approaches the 1.4-solar-mass limit.
31) According to present understanding, a nova is caused by ____
A) hydrogen fusion on the surface of a white dwarf
32) Which of the following is not true about differences between novae and supernovae?
Supernovae eject gas into space, but novae do not.
Will our Sun ever undergo a white dwarf supernova explosion? Why or why not?
No, because it is not orbited by another star.
When we see X-rays from an accretion disk in a binary system, we can’t immediately tell whether the accretion disk surrounds a neutron star or a black hole. Suppose we then observe each of the following phenomena in this system. Which one would rule out the possibility of a black hole?
intense X-ray bursts
