Mastering Astronomy Chapter: 12

The radius of a white dwarf is determined by a balance between the inward force of gravity and the outward push of _________
electron degeneracy pressure

A(n) __________ occurs when hydrogen fusion ignites on the surface of a white dwarf in a binary system.
nova

A(n) _________ occurs when fusion creates iron in the core of a star.
massive star supernova

A white dwarf in a close binary system will explode as a supernova if it gains enough mass to exceed the ________.
white dwarf limit (1.4 solar masses)

A(n) _______ consists of hot, swirling gas captured by a white dwarf (or neutron star or black hole) from a binary companion star.
accretion disk

A(n) ________ can occur only in a binary system, and all such events are thought to have the same luminosity.
white dwarf supernova

All of the single red-dwarf stars that ever formed are still on the main sequence today.
True

The Sun will get brighter as it begins to run out of fuel in its core.
True

A planetary nebula is the disk of matter around a star that will eventually form a planetary system.
False

The various stages of stellar evolution predicted by theory can best be tested by observations of stars in clusters.
True

A nova is a sudden outburst of light coming from an old main-sequence star.
False

It takes less and less time to fuse heavier and heavier elements inside a high-mass star.
True

In a core-collapse supernova, the outer part of the core rebounds from the inner, high-density core, destroying the entire outer part of the star.
True

Because of stellar nucleosynthesis, the spectra of old stars show more heavy elements than those of young stars.
False

A white dwarf is supported by the pressure of tightly packed
electrons

A star like the Sun will end up as a
White Dwarf

A white dwarf can dramatically increase in brightness only if it
Has another star nearby

Nuclear fusion in the Sun will
create elements up to and including oxygen.

Most of the carbon in our bodies originated in
the core of a red-giant star.

If the evolutionary track in Overlay 3, showing a Sun-like star, were instead illustrating a significantly more massive star, its starting point (stage 7) would be
up and to the left

A star (no matter what its mass) spends most of its life:
As a main sequence star

When a star’s inward gravity and outward pressure are balanced, the star is said to be
in hydrostatic equilibrium.

What temperature is needed to fuse helium into carbon?
100 million K

A star is on the horizontal branch of the H-R diagram. Which statement is true?
It is burning both hydrogen and helium.

During the hydrogen shell burning phase
the star grows more luminous.

A solar mass star will evolve off the main sequence when
it builds up a core of inert helium.

A surface explosion on a white dwarf, caused by falling matter from the atmosphere of its binary companion, creates what kind of object?
Nova

Virtually all the carbon-rich dust in the plane of the galaxy originated in
Low mass stars

An iron core cannot support a star because
iron cannot fuse with other nuclei to produce energy.

A 20 solar mass star will stay on the main sequence for 10 million years, yet its iron core can exist for only a
day

As a star’s evolution approaches the Type II supernova, we find

A.) helium to carbon fusion takes at least 100 million K to start.
B.) the heavier the element, the higher the temperature to fuse it.
C.) photo disintegration of iron nuclei begins at 10 billion K to ignite the supernova.
D.) the heavier the element, the less time it takes to make it.
E.) All of the above

All of the above

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

Which of the following best describes the evolutionary track of the most massive stars?
Horizontal right

If it gains sufficient mass, a white dwarf can become a
type I supernova.

For a white dwarf to explode entirely as a Type I supernova, it’s mass must be
1.4 solar masses, the Chandrasekhar Limit

The heaviest nuclei of all are formed
in the core collapse that set the stage of Type II supernovae.

The Chandrasekhar limit is
the upper mass limit for a white dwarf.

Where was supernova 1987a located?
in our companion galaxy, the Large Magellanic Cloud

Which of these events is not possible?
white dwarfs and companion stars producing recurrent Type I supernova events

Which of these does not depend on a close binary system to occur?
a Type II supernova

What can you conclude about a Type I supernova?
It was originally a low-mass star.

A recurrent nova could eventually build up to a
Type I supernova

The brightest stars of a young open cluster will be
massive blue main sequence stars.

Noting the turnoff mass in a star cluster allows you to determine its
age

Compared to a cluster containing type O and B stars, a cluster with only type F and cooler stars will be
older

Which stars in globular clusters are believed to be examples of mergers?
blue stragglers

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 these are correct.
All of these are correct.

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

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

Because they all involve formation of iron in cores of massive stars, all type II supernovae are equally luminous.
False

Because they all involve the detonation of a carbon-rich white dwarf at Chandrasekhar’s limit, all type I supernovae are equally luminous.
True

Novae are more closely related to type II than to type I supernovae.
False

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

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

Which of these is true of planetary nebulae?
They are ejected envelopes surrounding a highly evolved low-mass star.

Compared to our Sun, a typical white dwarf has
about the same mass and a million times higher density.

Which of these evolutionary paths is the fate of our Sun?
Planetary Nebula

Black dwarfs are
not found yet; the oldest, coldest white dwarf in the Galaxy has not cooled enough yet.

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

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.
True

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

A star system may undergo two or more nova outbursts.
True

Our Sun will eventually become a nova.
False

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

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

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

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

Elements heavier than iron are formed mainly in supernovae.
True

Supergiants are burning different fuels in several shells around the core.
True

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

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

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

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