Astronomy Ch. 12 Practice Test

As a main-sequence star, the Sun's hydrogen supply should last about 10 billion years from the zero-age main sequence until its evolution to the giant stages.

About 90% of the star's total life is spent on the main sequence.

Helium fusion requires a higher temperature than hydrogen fusion.

While more massive than most of its neighbors, our Sun is still technically a low-mass star.

The least massive red main-sequence stars may have lifetimes of a trillion years.

The main reason that stars evolved off the main sequence is because they are becoming less massive as energy is lost into space from the proton-proton cycle.

The initial rise off the main sequence in stage 8 comes from gravitational energy of the contracting helium core.

Paradoxically, while the core of the red giant is contracting and heating up, its radiation pressure causes its photosphere to swell up and cool off.

Once the helium flash occurs at stage 10, the star stabilizes again on the horizontal branch of the H-R diagram, but now hundreds of times as bright as on the main sequence.

The helium flash stage lasts several thousand years.

The helium flash increases the star's luminosity.

The luminosity of the red giant during its second trip to the upper right on the H-R diagram is less than before the helium flash expansion.

A star may undergo two or more red giant expansion stages.

The helium flash shows up on the H-R diagram on the way to the horizontal branch.

Our Sun will fade in luminosity as its suppl of hydrogen drops in a billion years.

A typical star burns helium for about the same amount of time it burns hydrogen.

Low-mass stars may become hundreds of times more luminous as giants than they were on the main sequence.

All stars have roughly the same luminosity after the helium flash.

Our Sun should become a planetary nebula in another 5 billion years.

A star system may ndergo two or more nova outbursts.

Our Sun will never become hot enough for carbon nuclei to fuse.

The density of white dwarf stars is about a million times that of the Sun.

The nova event is created by the helium flash.

Today the majority of the mass of the universe is already in the form of black dwarfs, the solution to the "dark matter" problem.

Our Sun will first become a red giant, then a white dwarf, and finally a brown dwarf.

As their name implies, all planetary nebulae feature spherical shells and look like the disks of Uranus or Neptune.

While there are none yet, in the very distant future, most normal matter will be in the form of black dwarfs.

Compared to the interstellar medium, the gases in a planetary nebula will be richer in helium and carbon.

Like emission nebulae, planetary nebulae glow because hot stars are causing the gases to ionize when exposed to strong ultraviolet radiation.

Although mass transfer can occur in binary stars, the small mass change does not impact the evolution of either companion.

A white dwarf's atoms have their electron orbitals crushed as closely as the Exclusion Principle allows.

White dwarfs were once the cores of stars that produced planetary nebulae.

Solar mass stars eventually become hot enough for carbon nuclei to fuse together.

It is the formation of iron in an evolved giant's core that triggers a Type II supernova event.

In the cores of the most massive stars, the electrons and protons fuse together and form neutrons.

Elements heavier than iron are formed mainly in supernovae.

Only low mass stars experience the temporary instability of the helium flash; high mass stars go directly into heavier element formation.

A massive star may change its color and size notably, but its high luminosity remains fairly constant.

The formation of carbon requires a core temperature of about 100 million K, but iron takes much higher temperatures and pressures.

Supergiant stars are burning different fuels in several shells around the core.

Our sun will likely die as a Type I supernova in about 5 billion years.

A star system can become a Type I supernova several times.

A massive star can fuse only up to the element silicon in its core.

The helium flash is followed within a few million years by the Type II supernova.

Supernova 1987A was the first supernova observed by astronomers since Gailileo first turned a telescope to the heavens.

While luminous enough to be seen with the naked eye, Supernova 1987A was, in fact, in our companion galaxy, the Large Magellanic Cloud.

Gold is rare since the only time it can be formed is during the core collapse of a supernova.

Chandrasekhar's limit is 1.4 times the mass of our Sun.

Because they all involve formation of iron in the cores of massive stars, all Type II supernovae are approximately equally luminous.

The number of Type I and Type II supernovae observed are approximately equal.

Because they all involve the detonation of carbon-rich white dwarf at the Chandrasekhar limit, all Type I supernovae are approximately equally luminous.

Neutrinos can move faster than the speed of light, as was discovered in SN1987A in 1987.

Novae are more closely related to Type II than to Type I supernovae.

If a white dwarf gains enough mass from a nearby star to exceed its Chandrasekhar limit it will become a nova.

A carbon-detonation supernova starts out as a white dwarf in a close binary system.

Most of the true energy released during a supernova is emitted as neutrinos.

Type II supernova spectra are poor in hydrogen because stars that explode this way use up all their hydrogen before they leave the main sequence.

Novae and Type II supernovae are essentially the same phenomena.

A 100 million year old open cluster will no longer contain any O type stars.

Globular clusters are dominated by bright red supergiants at the top right of the H-R diagram.

The blue stragglers represent the horizontal branch for globular clusters.

Blue stragglers are among the first stars formed in a cluster.

Supernova 1987A matched the theoretical predictions for Type I supernovae well.

The spectra of the oldest stars show the most heavy elements.

A star, no matter what its mass, spends most of its life as a A. protostar B. main-sequence star C. planetary nebula D. red giant or supergiant E. T-Tauri variable star

When a star's inward gravity and outward pressure are balanced, the star is said to be A. in gravitational collapse B. in thermal expansion C. in rotational equilibrium D. in hydrostatic equilibrium E. a stage 2 protostar

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

When a low mass star first runs short of hydrogen in its core, it becomes brighter because A. it explodes as a nova B. helium fusion gives off more energy than does hydrogen C. its outer, cooler layers are shed, and we see the brighter central core D. the core contracts, raising the temperature and extending the hydrogen burning shell outward E. the helium flash increases the size of the star immensely

A star is on the horizontal branch of the H-R diagram. Which statement is true? A. it is burning both hydrogen and helium B. it is about to experience the helium flash C. it is burning only helium D. the star is contracting E. the star is about to return to the main sequence

The helium flash converts helium nuclei into A. boron B. beryllium C. carbon D. oxygen E. iron

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

Can a star become a red giant more than once? A. yes, before and after the helium flash B. yes, before and after the Type II supernova event C. no, the planetary nebula blows off all the outer shells completely D. no, it will lose so much mass as to cross the Chandrasekhar Limit E. no, or we would see them as the majority of naked-eye stars

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

A white dwarf has the mass of the Sun and the volume of A. Jupiter B. Earth C. Mars D. the Moon E. Eros

The outward pressure in the core of a red giant balances the inward pull of gravity when A. the electron orbits are compressed so much they are all in contact B. the electrons and protons have combined to form neutrons C. hydrogen begins fusing into helium D. carbon fuses into heavier elements E. iron forms in the inner core

Which of these is true of planetary nebulae? A. They are expelled by the most massive stars in their final stages before supernova B. they are rings of material around protostars that will acrete into planets int time C. they are ejected envelopes surrounding a highly evolved low-mass star D. they are the envelopes that form when blue stragglers merge E. they are the material which causes the eclipses in eclipsing binary systems

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 hundred times lower density D. a smaller mass and half the density E. a smaller mass and twice the density

A(n) __________ represents a relatively peaceful mass loss as a red giant becomes a white dwarf. A. nova B. emission nebula C. supernova remnant D. planetary nebula E. supernova

A surface explosion on a white dwarf, caused by falling matter from the atmosphere of its binary companion, creates what kind of object? A. hypernova B. nova C. gamma ray burstar D. type I supernova E. type II supernova

Which of these evolutionary paths is the fate of our Sun? A. brown dwarf B. supernova of Type II C. pulsar D. planetary nebula E. nova

When the outer envelope of a red giant escapes, the remaining carbon core is called a A. black dwarf B. white dwarf C. planetary nebula D. black hole E. brown dwarf

The initial mass of a protostar generally determines the star's future evolution. But in some cases, what can alter this process? A. the star may be isolated in space, far from other influences B. the star may be in a spectroscopic binary system C. the star may gain mass by passing through a dark cloud D. the tar may collide with another, unrelated star E. the star may drift away from the other stars in its formation cluster

Black dwarfs are A. very common, making up the majority of the dark matter in the universe B. often made from very low mass protostars that never fuse hydrogen C. rare, for collapsing cores of over three solar masses are uncommon D. rare, for few binary systems are close enough for this merger to happen E. not found yet; the oldest, coldest white dwarf in the Galaxy has not cooled enough yet

Virtually all the carbon-rich dust in the plane of the galaxy originated in A. low-mass stars B. high-mass stars C. planetary nebulae D. white dwarfs E. brown dwarfs

You observe a low-mass helium white dwarf. What can you conclude? A. it is over 100 billion years old B. it will soon be a type II supernova C. it is part of a binary star system D. its core is mostly carbon E. it was once a blue supergiant

Of the elements in your body, the only one not formed in stars is A. hydrogen B. carbon C. calcium D. iron E. aluminum

An iron core cannot support a star because A. iron is the heaviest element, and sinks upon differentiation B. iron has poor nuclear binding energy C. iron cannot fuse with other nuclei to produce energy D. iron supplies too much pressure E. iron is in the form of a gas, not a solid, in the center of a star

A 20-solar-mass star will stay on the main sequence for 10 million years, yet its iron core can exist for only a A. day B. week C. month D. year E. century

As a star's evolution approaches the Type II supernova, we find A. the heavier the element, the less time it takes to make it B. the heavier the element, the higher the temperature to fuse it C. helium to carbon fusion takes at least 100 million K to start D. photo disintegration of iron nuclei begins at 10 billion K to ignite the supernova E. all of the above are correct

As a 6 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

Which of the following best describes the evolutionary track of the most massive stars? A. diagonally to lower right, then vertical, then horizontal left B. horizontally right, diagonal to lower left, then horizontal right C. horizontal right, then a clockwise loop D. horizontal right E. vertically left, then straight down

Type II supernovae occur when their cores start making A. carbon B. oxygen C. silicon D. iron E. uranium

If it gains sufficient mass from a binary companion, a white dwarf can become a A. brown dwarf B. type II supernova C. type I supernova D. planetary nebula E. black dwarf

For a white dwarf to explode entirely as a Type I supernova, its mass must be A. at least 0.08 solar mass B. 1.4 solar mass, the Chandrasekhar limit C. 3 solar masses, the Schwartzschild limit D. 20 solar masses, the Hubble limit E. 100 solar masses, the most massive known stars

The heaviest nuclei of all are formed A. in the horizontal branch B. in dense white dwarfs C. during nova explosions D. in the ejection of matter in the planetary nebula E. in the core collapse that sets the stage for Type II supernovae

The Chandrasekhar limit is A. an upper-mass limit for a white dwarf B. the temperature at which hydrogen fusion starts C. the temperature at which helium fusion starts D. the point at which a planetary nebula forms E. the lower-mass limit for a Type II supernova

Where was supernova 1987A located? A. in the Orion Nebula, M42 B. in Sagittarius, near the Galactic Nucleus C. in our companion galaxy, the Large Magellanic Cloud D. in M13, one of the closest of the evolved globular clusters E. near the core of M31 the Andromeda Galaxy

Which of these events is not possible? A. low-mass starts swelling up to produce planetary nebulae B. red giants exploding as Type II supernovae C. close binary stars producing recurrent novae explosions D. white dwarfs and companion starts producing recurrent Type I supernova events E. a white dwarf being found in the center of a planetary nebula

Which of these does not depend on a close binary system to occur? A. a nova B. a Type I supernova C. a Type II supernova D. all of these need mass transfer to occur E. none of these depend on mass transfer

What can you conclude about a Type I supernova? A. it was originally a low-mass star B. it was originally a high-mass star C. its spectrum will show large amounts of hydrogen D. its core was mostly iron E. the star never reached the Chandrasekhar limit

A recurrent nova could eventually build up to a A. planetary nebula B. Type I supernova C. Type II supernova D. hypernova E. quasar

The brightest stars in a young open cluster will be A. Cepheid variables B. massive blue main-sequence stars C. red giants D. yellow main-sequence stars like the Sun E. T-Tauri variables

What is the typical age for a globular cluster associated with our Milky Way? A. a few million years B. 200 million years C. a billion years D. 10-12 billion years E. 45 billion years

Which is used observationally to determine the age of a star cluster? A. the total number of main-sequence stars B. the ratio of giants to supergiants C. the luminosity of the main-sequence turn-off point D. the number of white dwarfs E. the amount of dust that lies around the cluster

Noting the main sequence turnoff mass in a star cluster allows you to determine its A. distance B. radial velocity C. age D. total mass E. number of stars

The brightest stars in aging globular clusters will be A. core stars of planetary nebulae B. massive blue main-sequence stars like Spica C. blue stragglers D. red supergiants like Betelgeuse and Antares E. blue supergiants like Rigel and Deneb

In a very young cluster, while most massive stars are swelling up into giants, the least massive stars are A. also evolving off the main sequence as well B. continuing to shine as stable main-sequence stars C. blowing off shells as planetary nebula instead D. collapsing directly to white dwarfs E. still on the zero-age main sequence

Compared to a cluster containing type O and B stars, a cluster with only type F and cooler stars will be A. younger B. older C. further away D. more obscured by dust E. less obscured by dust

Which stars in globular clusters are believed to be examples of mergers? A. eclipsing binaries B. blue supergiants C. blue stragglers D. brown dwarfs E. planetary nebulae cores

What was most surprising about SN1987A? A. the parent star was a blue supergiant, much like Deneb or Rigel B. the supernova was luminous enough to see with the naked eye C. the supernova was not even in our own Galaxy D. it did not produce the flood of neutrinos our models had led us to expect E. its pulsar appeared within weeks of the explosion

What made supernova 1987A so useful to study? A. we saw direct evidence of nickel to iron decay in its light curve B. its progenitor had been observed previously C. in the Large Magellanic Cloud, we already knew its distance D. it occurred after new telescopes, such as Hubble, could observe it very closely E. all of the above are correct