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Which two energy sources can help a star maintain its internal thermal pressure?

nuclear fusion and gravitational contraction

What type of star is our Sun?

A low-mass star

Which of the following masses separates low mass stars from high mass stars?

About solar masses

No stars are expected with masses greater than times our Sun because?

they would generate so much power that they would blow themselves apart.

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,

its surface temperature increases and its luminosity decreases.

When does a star become a main-sequence star?

when the rate of hydrogen fusion in the star's core is high enough to sustain gravitational equilibrium

Which of the following statements about degeneracy pressure is not true?

Degeneracy pressure varies with the temperature of the star.

What is the fate of an isolated brown dwarf?

It will remain a brown dwarf forever.

What percentage of a star's total lifetime is spent on the main sequence?

%

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 from, a red giant is

cooler and brighter.

At approximately what temperature can helium fusion occur?

million K

Why does a star grow larger after it exhausts its core hydrogen?

Hydrogen fusion in a shell outside the core generates enough thermal pressure to push the upper layers outward.

Helium fusion results in the production of

carbon.

What happens after the helium flash?

The core quickly heats up and expands.

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 dwarf

Compared to the star it evolved from, a white dwarf is

hotter and dimmer.

Most interstellar dust grains

are produced in the atmospheres of red giant stars.

Based on its main-sequence turnoff point, the age of this cluster is

about billion years.

Which statement about this cluster is not true?

It is the type of cluster known as an open cluster of stars.

Consider the star to which the arrow points. How is it currently generating energy?

by hydrogen shell burning around an inert helium core

Consider the star to which the arrow points. Which of the following statements about this star is not true?

It is significantly less massive than the Sun.

What is the CNO cycle?

a type of hydrogen fusion that uses carbon, nitrogen, and oxygen atoms as catalysts

Which element has the lowest mass per nuclear particle and therefore cannot release energy by either fusion or fission?

iron

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

Which of the following statements about the stages of nuclear burning in a massive star is not true?

Each successive stage lasts for approximately as long as the first, hydrogen fusion stage.

Suppose the star Betelgeuse (the upper left shoulder of Orion were to become a supernova tomorrow (as seen here on Earth. What would it look like to the naked eye?

Betelgeuse would remain a dot of light but would suddenly become so bright that, for a few weeks, we'd be able to see this dot in the daytime.

Which event marks the beginning of a supernova?

the sudden collapse of an iron core into a compact ball of neutrons

After a supernova event occurring in a high-mass star, what is left behind?

either a neutron star or a black hole

Why is Supernova A particularly important to astronomers?

It was the nearest supernova detected in nearly years.

The interstellar clouds called molecular clouds are ________.

the cool clouds in which stars form

What is a protostar?

a star that is still in the process of forming

Most interstellar clouds remain stable in size because the force of gravity is opposed by ________ within the cloud.

thermal pressure

Which part of the electromagnetic spectrum generally gives us our best views of stars forming in dusty clouds?

infrared

What kind of gas cloud is most likely to give birth to stars?

a cold, dense gas cloud

Which of the following phenomena is not commonly associated with the star formation process?

intense ultraviolet radiation coming from a protostar

When does a protostar become a main-sequence star?

when the rate of hydrogen fusion becomes high enough to balance the rate at which the star radiates energy into space

Approximately what core temperature is required before hydrogen fusion can begin in a star?

million K

Which star spends the longest time in the protostellar phase of life?

a solar mass star

What is the approximate range of masses that newborn main sequence stars can have?

. to solar masses

The vast majority of stars in a newly formed star cluster are ________.

less massive than the Sun

Which of the following statements about brown dwarfs is not true?

Brown dwarfs eventually collapse to become white dwarfs.

What can we learn about a star from a life track on an H-R diagram?

the surface temperature and luminosity the star will have at each stage of its life

Which of the following lists the stages of life for a low-mass star in the correct order?

protostar, main-sequence star, red giant, planetary nebula, white dwarf

What happens when a main-sequence star exhausts its core hydrogen fuel supply?

The core shrinks while the rest of the star expands.

The main source of energy for a star as it grows in size to become a red giant is ________.

hydrogen fusion in a shell surrounding the central core

The overall helium fusion reaction is:

Three helium nuclei fuse to form one carbon nucleus.

What is a helium flash?

The sudden onset of helium fusion in the core of a low-mass star

What is a planetary nebula?

Gas ejected from a low-mass star in the final stage of its life.

The ultimate fate of our Sun is to ________.

become a white dwarf that will slowly cool with time

What is the CNO cycle?

a set of steps by which four hydrogen nuclei fuse into one helium nucleus

In order to predict whether a star will eventually fuse oxygen into a heavier element, you mainly want to know what fact about the star?

its mass

Why is iron significant to understanding how a supernova occurs?

Iron cannot release energy either by fission or fusion.

After a supernova explosion, the remains of the stellar core ________.

may be either a neutron star or a black hole

Why is Supernova A particularly important to astronomers?

It is the nearest supernova to have occurred at a time when we were capable of studying it carefully with telescopes.

Algol consists of a . MSun main-sequence star and a . MSun subgiant. Why does this seem surprising, at least at first?

The two stars should be the same age, so we'd expect the subgiant to be more massive than the main-sequence star.

Where does gold (the element come from?

it is produced during the supernova explosions of high-mass stars

Which two processes can generate energy to help a star maintain its internal thermal pressure?

nuclear fusion and gravitational contraction

Our Sun is considered to be a ________.

low-mass star

Which process is required to allow a gravitationally-collapsing gas cloud to continue to collapse?

The cloud must radiate much of its thermal energy.

Angular momentum plays an important role in star formation. Which of the following characteristics of a protostellar system is probably not strongly affected by the star's angular momentum?

the onset of core hydrogen fusion

Generally speaking, how does the surface temperature and luminosity of a protostar compare to the surface temperature and luminosity of the main-sequence star it becomes?

A main-sequence star is hotter and dimmer than it was as a protostar.

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