Astrophysics Chapters 7-8

Which of the following is NOT considered in making a simple stellar model?

magnetic field

What prevents the enormous amount of energy released from the fusion reactions at a star's core from blowing the star apart?

gravity

Why does fusion require a high temperature?

to overcome the repulsive force between the protons

Where in the sun is the law of hydrostatic equilibrium at work?

at every point inside the sun

Where in the sun does nuclear fusion occur?

the core

Why does fusion occur in the layer(s) that it does?

Only the core is hot enough.

What is a protostar's energy source?

gravitational energy

What would happen in the interior of a normal star if gravity were to shrink the star's size a small amount?

all of the below

What happens to the neutrinos that are produced in the proton-proton chain?

They head out of the sun at nearly the speed of light.

Why does a star's life expectancy depend on mass?

More massive stars have shorter lifetimes because their larger masses cause them to consume their fuel faster.

What force causes the contraction of a cloud of interstellar matter to form a star?

gravitational force

What eventually halts the slow contraction of a newly forming star?

nuclear fusion

As cold gas in interstellar space contracts, which of the following occurs?

all of the above

What solved the solar neutrino problem?

The discovery that neutrinos oscillate between three different types.

Which factor resists the contraction of a cloud of interstellar matter?

all of the below

Why is there a mass-luminosity relation for main sequence stars?

The more massive a star is, the higher the rate of fusion in the core is due to the larger weight pressing down on the inner layers. When the energy from the fusion reaction reaches the surface it radiates into space with a characteristic luminosity.

How does the sun maintain its energy output?

fusion of hydrogen nuclei

At what wavelengths can we observe the early stages of protostar formation?

infrared

What happens to the temperature and density inside a collapsing protostar?

Temperature and density both increase.

Which of the following statements accurately describe(s) some observed properties of supernovae type Ia and supernovae type II?

Supernovae type II have hydrogen lines in their spectra and supernovae type Ia are more luminous.

This figure shows the post main-sequence evolution of different stars on the H-R diagram. When the sun leaves the main sequence to become a giant, what happens to its surface temperature and luminosity?

The luminosity increases and the surface temperature decreases.

Suppose that you monitor the apparent brightness of a supernova and notice that 50 days after it reached maximum brightness, it has dimmed by 2 magnitudes. Examine the light curves in this figure. Which type of supernova are you most likely observing?

Type II

What changes would occur if the sun were replaced with a one-solar-mass black hole?

Earth's orbit would not change and the planets would disappear from view.

What happens to white dwarfs as they age?

their surface temperatures decrease and luminosity decreases

How can you estimate the age of a star cluster?

by its brightest stars

What is the turnoff point of a star cluster?

the location on the H-R diagram where stars are leaving the main sequence

What prevents gravity from shrinking a white dwarf to a smaller size?

degenerate electrons

What event marks the end of every star's main-sequence life?

the end of hydrogen fusion in the core

Which is true for the H-R diagram of a star cluster that has many hot, blue, luminous stars?

It will have stars over most of the main sequence.

Why do supernova remnants emit x-rays?

because they are filled with hot gas

Why do the millisecond pulsars spin so fast?

Accretion of matter from a nearby binary companion spins them up.

Why do we expect that neutron stars spin rapidly?

the law of conservation of angular momentum

Which is not true about a type I supernova?

It involves a massive star.

Which is not true about a type II supernova?

It occurs in a binary system.

What is one of the reasons astronomers don't use visible-wavelength telescopes to locate neutron stars?

Neutron stars are very small.

How can a black hole emit X-rays?

X-rays emitted just before material crosses the event horizon can escape the gravitational pull.

What observational evidence do we have that stellar-death black holes really exist?

Some X-ray binaries have unseen objects with masses greater than 3 solar masses.

A star moves off the ZAMS after burning up what element?

Hydrogen

Which is a reason that a neutron star may not be observed from Earth as a pulsar?

All of the above are reasons that a neutron star may not be observed as a pulsar from Earth.

What is meant by "Every pulsar is a neutron star, but not every neutron star is a pulsar"?

Some neutron stars do not emit "pulses" of radiation for various reasons.

How are the ages of star clusters related to their turnoff points?

The age of a cluster is the life expectancy of stars at its turnoff point and the lower the turnoff point, the older the star cluster.

Which is true for the event horizon of a black hole?

All of the above

What evidence is there that black holes have event horizons?

both of the above

How does the main-sequence lifetime of a star compare to its entire fusion lifetime?

Stars spend about 90% of their fusion lifetimes on the main sequence.

Why can't massive stars generate energy from iron fusion?

Iron fusion consumes energy.

Why does an expanding giant star become cooler?

Energy is absorbed in expanding and lifting the gas.

Ultimately a sun-like star will become which of the following?

white dwarf

Why can't the lowest-mass stars have the same fate as the sun-like stars?

They are not massive enough to collapse to such a high density.

What property does matter inside the event horizon of a black hole retain?

mass, angular momentum, and electric charge

White dwarfs and neutron stars are both end products of stellar evolution. White dwarfs are composed of mostly carbon, oxygen, and electrons, whereas neutron stars are composed of mostly neutrons. What happens to the protons in the atomic nuclei and the degenerate electrons that were inside the star that creates a neutron star?

The electrons and protons combine to form neutrons and neutrinos.

What prevents neutron stars from contracting to a smaller size?

degenerate neutrons

Which of the following is an accurate description of the Schwarzschild radius?

It is the radius to which an object must shrink to become a black hole and is the radius of the event horizon surrounding a black hole singularity.

Which is true for X-ray bursters?

How do X-ray bursters resemble a nova?

all of the above

How much longer will the sun last?

about 5 billion years

What is the lower limit for the mass of neutron stars?

about 1.4 solar masses

What is the Schwarzschild radius?

all of the above

If the sun has a Schwarzschild radius, why isn't it a black hole?

It is not massive enough.

What is the Schwarzschild radius of an object?

It can be any size, depending on the mass of an object.

Which type of supernova leaves NO core remnant?

supernova type Ia

Why are neutron stars expected to be hot?

Why are neutron stars expected to spin fast?

Why are neutron stars expected to have strong magnetic fields?

Thy are so compact.