Deck 10: Star Formation and Evolution

Question 1

The birth of stars is a battle between gravity and radiation pressure.

Answer 1

True

Question 2

When a star becomes a red giant, its core expands to a roughly proportional larger size too.

Answer 2

False

Question 3

The gas in the interstellar medium consists of mostly heavy elements.

Answer 3

False

Question 4

Evolution of a star off the main sequence is caused by the loss of mass from hydrogen fusion by the star while a main sequence star.

Question 5

Most stars are usually formed singularly or as binaries, not in clusters.

Question 6

What effect do even thin clouds of dust have on light passing through them?

A) The light that passes though them is blue shifted due to the cloud's approach.
B) It dims the light of all more distant stars.
C) Even a little can completely block all light, such as the Horsehead Nebula.
D) Its motion causes the light of stars beyond to twinkle.
E) Its motion causes all light to be redshifted as it passes through these clouds.

Question 7

Eventually, all low mass stars will become white, then black, dwarfs.

Question 8

When helium fusion begins in a one solar mass main star, it begins gradually, with this rate slowly increasing over time.

Question 9

For our Sun, the production of carbon will be the end of its nucleosynthesis.

Question 10

The fundamental difference between a protostar and a star is that the latter has nuclear fusion as its energy source and the former does not.

Question 11

All planetary nebulae are slowly-expanding spherical disks ejected by red giants, while their exposed cores appear as white dwarfs.

Question 12

The Orion Nebula glows strongly in the infrared.

Question 13

Interstellar matter is distributed very evenly through the galaxy.

Question 14

As a star begins to evolve away from the main sequence, it gets larger.

Question 15

Hydrogen is the major gas in the interstellar medium.

Question 16

Interstellar gas is composed of

A) only hydrogen.
B) 90% hydrogen, 9% helium by weight.
C) 10% hydrogen, 90% helium by numbers of atoms.
D) some hydrogen, but mainly carbon dioxide.
E) ammonia, methane, and water vapor.

Question 17

It takes about 10³² hydrogen atoms to make a star.

Question 18

Modern astronomers have observed the complete life cycle for many stars, making stellar evolution one of the best-tested astronomical theories.

Question 19

Protostars have not been observed, but are consistent with observations of young main sequence stars.

Question 20

The shell ejection in making a planetary is spherical and symmetrical in all cases.

Question 21

A solar mass star will evolve off the main sequence when

A) it completely runs out of hydrogen.
B) it expels a planetary nebula to cool off and release radiation.
C) it explodes as a violent nova.
D) it builds up a core of inert helium.
E) it loses all its neutrinos, so fusion must cease.

Question 22

Stars form from a collapsing cloud that fragments into smaller and smaller pieces. This process takes about

A) 10,000 years.
B) 25,000 years.
C) 100,000 years.
D) a few million years.
E) 100 million years.

Question 23

What inevitably forces a star like the Sun to evolve away from being a main sequence star?

A) The core begins fusing iron.
B) The star uses up all its supply of hydrogen.
C) The carbon detonation explodes it as a type I supernova.
D) Helium builds up in the core, while the hydrogen burning shell expands.
E) The core loses all its neutrinos, so all fusion ceases.

Question 24

How long does it take for a star like our Sun to form?

A) 100 thousand years
B) Two million years
C) Fifty million years
D) One billion years
E) 4.6 billion years

Question 25

Protostars can be observed in

A) the Crab Nebula.
B) the Andromeda Galaxy.
C) the Orion Nebula.
D) our Solar System.
E) the Helix Nebula.

Question 26

The "helium flash" occurs at what stage in stellar evolution?

A) When the T Tauri bipolar jets shoot out
B) In the middle of the main sequence stage
C) Red giant
D) Horizontal branch
E) Planetary nebula

Question 27

Just as a low-mass main sequence star runs out of fuel in its core, it actually becomes brighter. How is this possible?

A) Helium fusion gives more energy than hydrogen fusion does, based on masses.
B) Its outer envelope is stripped away and we see the brilliant core.
C) The core contracts, raising the temperature and increasing the size of the region of hydrogen shell-burning.
D) It explodes.
E) It immediately starts to fuse helium.

Question 28

During the hydrogen shell burning phase

A) the star grows more luminous.
B) the star becomes less luminous.
C) helium is burning in the core.
D) the core is expanding.
E) hydrogen is burning in the central core.

Question 29

What is the force that keeps a main sequence star from blowing apart?

A) Magnetism
B) Gravitation
C) The strong force
D) Radiation pressure
E) Electron degeneration pressure

Question 30

The spectra of interstellar gas clouds show that they have the same basic composition as

A) interstellar dust.
B) Earth's atmosphere.
C) stars.
D) asteroids.
E) the Martian polar caps.

Question 31

Which event marks the birth of a star?

A) Formation of the planetary nebula
B) Fusion of hydrogen atoms into helium atoms
C) Collapse of an interstellar cloud
D) Formation of a photosphere
E) Instability in an interstellar cloud

Question 32

Which statement is TRUE about the interstellar medium?

A) Gas contains a lot of carbon atoms.
B) Dust blocks the longest electromagnetic wavelengths.
C) Gas obscures the light from distant stars.
D) We know more about the gas than the dust.
E) Dust is spread uniformly through the galaxy.

Question 33

What happens when an interstellar cloud fragment shrinks?

A) It first becomes opaque.
B) Density rises.
C) Temperature rises.
D) Pressure rises.
E) all of the above

Question 34

The stars found in nebulae like the Orion Nebula probably formed

A) within the last few million years.
B) about 10 million years ago.
C) hundreds of millions of years ago.
D) billions of years ago.
E) at the beginning of the universe.

Question 35

What temperature is needed to fuse helium into carbon?

A) 5,800 K
B) 100,000 K
C) 15 million K
D) 100 million K
E) One billion K

Question 36

The density of interstellar dust is very low, yet it still blocks starlight because

A) it is so cold it absorbs higher energy photons.
B) there is 100 times more opaque gas than dust present in the ISM.
C) the dust particles are about the same size as the light waves they absorb.
D) the dust particles are irregular in shape.
E) ice particles reflect all light back toward their stars, not toward us.

Question 37

If the initial interstellar cloud in star formation has a mass sufficient to form hundreds of stars, how does a single star form from it?

A) One star forms at its center and blows the rest of the matter back into space.
B) The cloud fragments into smaller clouds and forms many stars at one time.
C) One star forms and the rest of the matter goes into making planets, moons, and other objects of a solar system.
D) The cloud is disrupted by rotation so that it reduces its mass down to that of a typical star.
E) A supernova blows the cloud up and dissipates the majority of the gas.

Question 38

Some regions along the plane of the Milky Way appear dark because

A) there are no stars in these areas.
B) stars in that region are hidden by interstellar gas.
C) stars in that region are hidden by dark dust particles.
D) many brown dwarfs in those areas absorb light which they turn into heat.
E) many black holes absorb all light from those directions.

Question 39

In the Milky Way galaxy, gas and dust are found

A) in molecular clouds.
B) everywhere.
C) in neutral hydrogen clouds.
D) in dark nebulae.
E) in emission nebulae.

Question 40

A typical protostar may be several thousand times more luminous than the Sun. What is the source of this energy?

A) Chemical combustion of hydrocarbons
B) Nuclear fusion in its core
C) From the release of gravitational energy as the protostar continues to shrink
D) The ionization of the gas as it heats up
E) From nearby hot stars or supernovae that have initiated the star formation process

Question 41

What is the source of the large dust shells seen around some red giants and red supergiants?

A) Leftover material from their formation
B) Debris left behind by a supernova
C) Material from winds from these same stars
D) Debris left behind by passing comets
E) Star-forming molecular clouds

Question 42

What are the characteristics of an open cluster of stars?

A) Mostly found above and below the galactic plane
B) Old age and millions of members
C) A few hundred, mainly main sequence stars
D) All stars are much more massive than our Sun.
E) All stars are about the same age and luminosity.

Question 43

What are black dwarfs?

A) The lowest mass main sequence stars
B) The end result of massive star evolution
C) Objects that are not quite massive enough to be stars
D) Pulsars that have slowed down and stopped spinning
E) Cooled off white dwarfs that no longer glow visibly

Question 44

A high-mass star dies more violently than a low-mass star because

A) it must always end up as a black hole.
B) it generates more heat and its core eventually collapses very suddenly.
C) it cannot fuse elements heavier than carbon.
D) gravity is weakened by its high luminosity.
E) it is most often found as part of a binary system.

Question 45

Compared to our Sun, a typical white dwarf has

A) about the same mass and density.
B) about the same mass and a million times higher density.
C) a larger mass and a 100 times lower density.
D) a smaller mass and half the density.
E) a smaller mass and twice the density.

Question 46

As a 4-10 solar mass star leaves the main sequence on its way to becoming a red supergiant, its luminosity

A) decreases.
B) first decreases, then increases.
C) increases.
D) remains roughly constant.
E) first increases, then decreases.

Question 47

Which of the following best describes the evolutionary track followed on the H-R diagram for the most massive stars?

A) Vertically upward, along the left edge of the diagram
B) Diagonally to lower right, then vertical, then horizontally left
C) Horizontally right, diagonally to lower left, then horizontally right
D) Horizontally right
E) Horizontally right, then forms a clockwise loop

Question 48

What are the characteristics of globular cluster stars?

A) No stars as hot as our Sun
B) Old age and hundreds of thousands to millions of member stars
C) No main sequence stars left, with billions of member stars
D) A few hundred stars, most still on the main sequence
E) Hundreds of light years across, with bright OB stars dominant

Question 49

Isolated main-sequence stars as massive as 10 to 12 times the mass of the Sun may still manage to avoid going supernova. Why?

A) Because they can also have strong stellar winds
B) Because about half that mass will be contained in the carbon core
C) Because they would be classified as brown dwarfs
D) Because these stars will eject at least 4 solar masses in the planetary nebula stage
E) Because their masses will decrease as they fuse heavy elements into lighter elements in their cores

Question 50

The order of evolutionary stages of a star like the Sun would be Main Sequence, giant, planetary nebula, and finally

A) hypernova.
B) neutron star.
C) white dwarf.
D) nova.
E) black hole.

Question 51

What is a planetary nebula?

A) The bipolar jets ejected by a T Tauri variable
B) A planet surrounded by a glowing shell of gas
C) The disc of gas and dust surrounding a young star that will soon form a solar system
D) The ejected envelope, often bipolar, of a red giant surrounding a stellar core remnant
E) A type of young, medium mass star

Question 52

Which type of star has the strongest stellar winds?

A) Giant K- and M-type stars
B) White dwarfs
C) Dwarf K- and M-type stars
D) Main sequence O- and B-type stars
E) T Tauri stars

Question 53

All globular clusters in our Milky Way are about how old?

A) Less than a million years
B) Ten-fifty million years old
C) One to three billion years old
D) Around ten billion years old
E) A variety of ages, from newly born to twenty billion years old

Question 54

Eta Carinae is an example of a

A) black hole.
B) supermassive star.
C) red dwarf.
D) nebula.
E) stellar nursery.

Question 55

Which of the following is TRUE regarding planetary nebulae?

A) Some are spherical, but most have bipolar structure.
B) They are the result of the mass loss during the main sequence stage of the most massive stars.
C) They are the rings of material surrounding newly formed stars that will eventually form the planetary systems.
D) They are the ejected envelopes of highly evolved brown dwarf stars.
E) They are the coronas surrounding most blue stragglers.

Question 56

Why are star clusters almost ideal "laboratories" for stellar studies?

A) All stars in the cluster are the same size and luminosity.
B) Their combined light makes them much easier to spot from a distance.
C) Stars in clusters have the same age, similar composition, and are at the same distance away.
D) Stars in clusters are all relatively young and therefore shine brightly.
E) Like our Sun, stars in clusters are always located in the plane of the Milky Way Galaxy.

Question 57

The most important fact about a cluster of stars that makes them useful for studying star formation is that

A) all the stars formed from the same cloud.
B) all the stars formed at about the same time.
C) all the stars are at the same distance from Earth.
D) all the stars have the same chemical composition.
E) all the stars are the same spectral type.

Question 58

The birthplaces of stars correspond to the ________ clouds in the interstellar medium.

Question 59

Most stars in the Milky Way probably formed

A) alone.
B) in intergalactic space, then were swept up into the Galaxy.
C) in clusters in the Galaxy's spiral arms.
D) from planetary nebulae.
E) in the galactic Nucleus, then migrated outward later.

Question 60

Which of these will the Sun probably become in the very distant future?

A) Hypernova
B) Supernova
C) Pulsar
D) Planetary nebula
E) Nova

Question 61

What is causing the Trifid Nebula to glow?

Question 62

What event marks the birth of a new star?

Question 63

The Main Sequence is the first stellar stage in which energy produced by ________ balances the energy lost by radiation from the surface of the star.

Question 64

During various stages of evolution, low mass stars (like the Sun) differ significantly from high mass stars. How and why are the main sequence lifetimes different?

Question 65

Why can we say a star spends its life trying to maintain equilibrium?

Question 66

An interstellar gas cloud has the mass to form hundreds of stars. What generally happens to it?

Question 67

What is a helium flash?

Question 68

During various stages of evolution, low mass stars (like the Sun) differ significantly from high mass stars. How do they differ in terms of observational properties while Main Sequence stars?

Question 69

Why can radio waves get through the dust clouds, but light is blocked?

Question 70

When a low-mass star runs out of hydrogen in its core, it gets brighter. Why?

Question 71

Discuss the relationship between young stars, the interstellar medium and nebulae.

Question 72

A ________ stage is a relatively gentle mass-loss event which allows a star to peacefully readjust its structure into a white dwarf configuration.

Question 73

A protostar develops a bipolar flow of gas when it is still surrounded by an equatorial disk of ________.

Question 74

In an H-R Diagram, the path showing changes in a star's luminosity and surface temperature as a function of time is called its ________.

Question 75

Contrast the chemical composition of interstellar gas with that of interstellar dust.

Question 76

Why does gravitational contraction halt in collapsing protostars?

Question 77

What element are most white dwarfs primarily made of? Why?

Question 78

The Trifid Nebula is an example of a(n) ________ nebula.

Question 79

The order of evolutionary stages of a star like the Sun would be Main Sequence, giant, planetary nebula, and finally a ________.

Question 80

Contrast the brightest stars of young open and old globular clusters.