Deck 22: Stars From Adolescence to Old Age

Question 1

Which of the following statements about the main sequence stage in the life of a star is FALSE?

A) all stars spend the majority of their lives in the main sequence stage
B) during the main sequence stage, energy to power the star is provided by the fusion of hydrogen
C) main sequence stars are rare in the Galaxy, so we are lucky to be living around one
D) different stars spend a different amounts of time (number of years) in the main sequence stage, depending on the characteristics they were born with
E) during the main sequence stage, the mass of any star does not change significantly

Answer 1

main sequence stars are rare in the Galaxy, so we are lucky to be living around one

Question 2

As a star becomes a giant, its outer layers are expanding. Where does the energy for expanding these layers come from?

A) from the fusion of helium into carbon in the core
B) from the long-term fusion of hydrogen into helium in the core
C) from an explosion in the core
D) from a magnetic dynamo effect in the star's outer layers, caused by a much stronger magnetic field inside the star
E) from the fusion of hydrogen into helium in a shell around the core

Answer 2

from the fusion of hydrogen into helium in a shell around the core

Question 3

If you wanted to discover the youngest stars you could find in some grouping of stars in the Galaxy, which type of star group would be the best to search?

A) globular clusters
B) open clusters
C) the type of clusters that form a halo around the disk of the Milky Way
D) stellar associations
E) all types of star groups have an equal number of young stars in them
Section 22.3 Checking Out the Theory

Answer 3

stellar associations

Question 4

On an H-R diagram of a cluster of stars, which characteristic of the diagram do astronomers use as a good indicator of the cluster's age?

A) the number of M stars on the main sequence
B) the lowest luminosity star that is visible in the cluster
C) the point on the main sequence where stars begin to "turn off" -- to move toward the red giant region
D) how high up on the main sequence M type stars are found
E) the coolest surface temperature for a star that they can measure

Question 5

A group of graduate students, bored during a cloudy night at the observatory, begin to make bets about the time different stars will take to evolve. If they have a cluster of stars which were all born at roughly the same time, and want to know which star will become a red giant first, which of the following stars should they bet on?

A) a star of about the same mass as our Sun
B) a star that would type O on the main sequence star
C) a star of about 1/2 the mass of our Sun
D) a star of about 8% the mass of our Sun
E) you can't fool me, all stars reach the red giant stage in roughly the same number of years
Section 22.2: Star Clusters

Question 6

How long a main sequence star remains on the main sequence in the H-R diagram depends most strongly on

A) its initial composition
B) the number of companion stars or planets orbiting it
C) its radial velocity (as measured from the spectrum)
D) its mass
E) its ability to fuse the element carbon into some other element

Question 7

As a cluster of stars begins to age, which type of star in the cluster will move off the main sequence of the H-R diagram first?

A) all the stars in a cluster are born at the same time; so they will all move off the main sequence at the same time, as they evolve
B) G type stars, like our Sun
C) M type stars, which are the coolest
D) the lowest mass stars, which have the least amount of fuel for fusion
E) the O and B type stars

Question 8

When the outer layers of a star like the Sun expand, and it becomes a giant, which way does it move on the H-R diagram?

A) toward the upper right
B) toward the upper left
C) toward the lower right
D) toward the lower left
E) it moves horizontally, but stays on the main sequence

Question 9

When a star first begins the long path toward becoming a red giant, a layer of hydrogen around the core begins to undergo fusion. If this layer was too cold to do fusion throughout the main sequence stage, why is it suddenly warm enough?

A) as the star expands, all the layers heat up
B) the core is collapsing under its own weight and heating up from the compression; this heats the next layer up
C) the heat comes from the fusion of carbon in the core, which starts right away
D) the heat comes from the outer layers of the star, which are much hotter than the core
E) this is an unsolved problem in astronomy, but something must be heating that layer, since we observe red giants out there

Question 10

How are globular clusters distributed in our Milky Way Galaxy?

A) completely randomly: you never know where we will find one
B) only in the main spiral disk of the galaxy
C) mostly in a large spherical halo (or cloud) surrounding the flat disk of the Galaxy
D) only in the very center of the Galaxy, really crowded together
E) where the giant molecular clouds are found

Question 11

A type of star cluster that contains mostly very old stars is

A) a globular star cluster
B) a stellar association
C) a galaxy
D) an HII region
E) an open cluster

Question 12

An astronomy student, for her PhD, really needs to estimate the age of a cluster of stars. Which of the following would be part of the process she would follow?

A) measure the Doppler shift of a number of the stars in the cluster
B) search for x-rays coming from the center of the cluster
C) plot an H-R diagram for the stars in the cluster
D) count the number of M type stars in the cluster
E) search for planets like Jupiter around the stars in the center of the cluster

Question 13

The event in the life of a star that begins its expansion into a giant is

A) the core reaches a temperature of ten million degrees
B) as much as 90% of the star explodes violently
C) almost all the hydrogen in its core that was hot enough for fusion has been turned into helium
D) the star's internal structure reaches equilibrium for the first time in its life
E) it reaches the stage that astronomers call the zero-age main sequence

Question 14

Why do all stars spend most of their lives on the main sequence?

A) because the neutrinos created inside the Sun do not carry any energy away with them
B) because during this stage the star contracts from enormous size to a relatively small ball; this takes a long time
C) because the fuel for energy production in this stage of the star's life is hydrogen; and that is an element every star has lots and lots of
D) because in this stage, the processes inside the star do not generate any energy; thus the star can continue in this stage indefinitely
E) this is an unsolved problem in astronomy, and is an important project for the world's largest telescopes to work on

Question 15

An eccentric Hollywood movie producer, vacationing in Australia, goes to an observatory and offers to make a big donation if they can show him a place in the Milky Way Galaxy where there are more than a million stars seen together. Which object would satisfy his extravagant tastes?

A) The bright HII region NGC 3576
B) The open star cluster NGC 6520
C) The inner part of M42, the Orion Nebula, a star forming region
D) The globular cluster Omega Centauri
E) Alpha Centauri, the nearest star system to the Sun

Question 16

Which of the following types of stars will spend the longest time (the greatest number of years) on the main sequence?

A) O
B) A
C) G
D) K
E) you can't fool me; every star spends about the same number of years on the main sequence

Question 17

Biologists tell us that life on Earth took billions of years to evolve into astronomy students and other examples of intelligent life. If we want to search for planets with intelligent life-forms that evolved over the same period of time that we did, what sorts of stars should we not bother searching around?

A) relatively low-mass main sequence stars
B) O and B type stars
C) G type stars
D) main sequence stars with surface temperatures of about 6,000 ^oK
E) all stars live such a long time that life as we know it can evolve around them even if it takes billions of years

Question 18

In a science fiction television show set in the far future, a starship finds itself approaching a stellar association. What types of objects would they be most likely to notice in such an association as they approach?

A) planets around most of the stars
B) bright O and B type stars
C) a very dense concentration of old stars right in the center of the association
D) many remnants of stars that have finished their lives long ago
E) the most noticeable thing would be the almost complete absence of any interstellar gas or dust in the area

Question 19

Which of the following statements about open clusters of stars is FALSE?

A) they typically contain more mass than any other type of cluster
B) their diameters are typically about 30 LY across
C) they are found mostly in the disk of our Galaxy
D) they are often associated with regions of interstellar matter (gas and dust)
E) they can contain stars of a wider range of ages than other types of star groups

Question 20

A science fiction writer needs an environment for her latest story where stars are as crowded together as possible. Which of the following would be a good place to locate her story?

A) in a small open cluster
B) in a stellar association
C) in the outer regions of a spiral galaxy's disk
D) in a globular cluster
E) in a popular Hollywood restaurant

Question 21

Many names used by astronomers are misleading or outdated. A good example is the term planetary nebula, which astronomers use to refer to:

A) a solar system in formation
B) the remains of an exploded high-mass star
C) a region of gas and dust where new planets have recently formed
D) the shell let go by a dying low-mass star
E) a globular cluster, which looks like a planet through very small telescopes

Question 22

If stars with masses like our Sun's cannot make elements heavier than oxygen, where are heavier elements like silicon produced in the universe?

A) these heavier elements were made in the Big Bang at the time the universe began, and have been part of the universe ever since
B) heavier elements are made in the proto-planetary disks that accompany many newly forming stars
C) heavier elements are made in the cores of significantly more massive stars than the Sun, which can get hotter in the middle
D) heavier elements are made in the cores of planets that are molten and hot when they form
E) this is an unsolved problem in astronomy; no one knows

Question 23

Which of the following statements about the mass of the Sun during its lifetime is correct?

A) It will have the same exact mass from birth to death
B) The only way the Sun loses mass is by turning a bit of mass into energy during fusion, and this loss is very small
C) The Sun will lose some mass during the late periods of its life, but the amount loss will be less than 1 %.
D) The Sun will lose a significant amount of mass during and after its red giant phase
E) The Sun will lose almost ALL of its mass before it dies; the remaining mass will be less than the mass of Jupiter.
Section 22.5: The Evolution of More Massive Stars

Question 24

Which of the following stages will our own Sun go through in the future:

A) spending a long time on the main sequence
B) expanding to become red giant
C) eventually fusing helium into carbon
D) giving off a planetary nebula
E) all of the above

Question 25

Why can a star with a mass like our Sun not fuse (produce) further elements beyond carbon and oxygen?

A) because there are no elements heavier than those two; they are the heaviest nuclei in nature
B) because they just cannot get hot enough for the fusion of heavier nuclei
C) because all such stars explode before they can make any other elements
D) because all such elements become radioactive and their nuclei break apart rather quickly
E) because the cores of such stars get too hot for further types of fusion to be able to happen

Question 26

When stars become giants, which of the following does NOT usually happen?

A) their outer envelopes expand significantly
B) they lose a significant amount of mass from their outside layers
C) their surface temperatures become lower than before
D) their overall luminosities increase
E) their mass grows significantly as they incorporate planets and interstellar matter near the star

Question 27

In a planetary nebula, the shell of expelled material is glowing intensely. What is the main source of energy for this glow?

A) friction, as the atoms of the expelled shell rub against each other
B) the explosion of the dying star
C) ultraviolet radiation from the collapsing hot star at the center
D) the fusion of hydrogen into helium in the nebula
E) the change of electrons and protons into neutrons

Question 28

The oldest structures in our Galaxy turn out to be

A) HII regions
B) giant molecular clouds
C) open clusters
D) stellar associations
E) globular clusters
Section 22.4: The Further Evolution of Stars

Question 29

When the core of a star reaches a temperature of about 100 million degrees (K), something new happens in the core. What is this new event?

A) hydrogen nuclei begin to fuse into heavy hydrogen (deuterium) and then into helium
B) two helium nuclei begin fusing of beryllium (element number 4)
C) the core explodes
D) three helium nuclei begin fusing carbon (element number 6)
E) the fusion of iron (element 26)

Question 30

Really massive stars differ from stars with masses like the Sun in that they

A) go through all the stages of their lives more slowly
B) do not really go through a main sequence stage in their lives
C) can fuse elements beyond carbon and oxygen in their hot central regions
D) are no longer forming in the Galaxy; they only formed very early in the Galaxy's history
E) they are significantly less luminous after the main sequence stage is over

Question 31

If we look back to the first generation of stars made when the Galaxy was first forming, how do they differ from stars being formed today?

A) the first generation stars never become red giants
B) the first generation stars all live their lives much more slowly than stars today (so they last a long time)
C) the first generation stars cannot form planets of any kind
D) the first generation stars contain little or no elements heavier than helium
E) I disagree; I think first generation stars will be like stars forming today in all ways

Question 32

If you trace back the history of a carbon atom in your little finger through all of cosmic history, where did this atom most likely originate?

A) it was made in the big bang
B) it was fused from hydrogen atoms during the main-sequence stage of a star's life long before the Sun existed
C) it was made from smaller nuclei in the hot core of the Earth when our planet first formed
D) it was fused from 3 helium nuclei in the core of a red giant star long before the Sun existed
E) it came from Bayonne, New Jersey (where a lot of carbon-rich soot originates)

Question 33

Why is it easier for red giants to lose mass than main sequence stars?

A) red giants are much hotter on their surfaces, allowing gases to move away
B) red giants are so big, the gravity at their surface (that holds material to the star) is less
C) red giants are made of carbon and oxygen throughout, which escape more easily
D) all red giants explode at the end of their lives
E) you can't fool me, stars lose the same amount of mass during every stage of their lives

Question 34

After it experiences a "helium flash" a star like the Sun will have a brief period of stability, fusing helium into carbon (and sometimes oxygen). During this brief stable stage, the star

A) gets to be even larger in diameter than it was as a red giant
B) returns to the position on the H-R diagram that the star had in its main-sequence stage
C) increases tremendously in luminosity
D) is able to fuse many of the heaviest elements (such as iron and gold) in its superhot core
E) none of the above

Question 35

If most stars are low-mass stars, and low-mass stars typically eject a planetary nebula, why then do astronomers see relatively few planetary nebulae in the sky?

A) planetary nebulae can only be detected through their faint radio emissions
B) planetary nebulae are only visible when a planet surrounding the star plows through the ejected material, causing it to glow
C) planetary nebulae expand rapidly and soon become too faint to be visible
D) planetary nebulae quickly fall back onto the star produced them
E) while most stars are low-mass when they are born, throughout their lives they gather more and more material; so few stars are low-mass when they die