AS101 Assignment 7

The Sun will eventually become a supernova.

False

Theory predicts that neutron stars may not exceed 3 solar masses.

True

When a star with a mass comparable to that of the Sun dies, it becomes a black hole.

False

If two stars are emitting the same amount of light, how will the star that is farther away appear?

dimmer

What aspect of a star is a measure of the total energy radiated by the star in one second?

luminosity

If you compare two stars, which one will always have the greater luminosity?

The one with the smaller absolute magnitude will always have the greater luminosity.

The nearest star, Proxima Centauri, is about four light-years away and has a luminosity about 0.001 times that of the Sun. If Proxima Centauri were at a distance of one light-year instead of four, how much brighter would it appear in the sky?

16 times as bright

How does a star's surface temperature determine the appearance of its spectrum?

Surface temperature determines the velocity of collision rates of atoms and ions and its colour

How do we know that giant stars are larger in diameter than the Sun?

They are more luminous but have about the same temperature.

Sirius A and B are two stars at the same distance from the Earth. In this binary system, Sirius A is much brighter but Sirius B is much hotter. From this information, what can you conclude about the two stars?

Sirius B must be much smaller than Sirius A.

In a Hertzsprung-Russell diagram, where are the stars with the smallest radius found?

in the lower left corner

A certain star moves from the middle toward the top right of the Hertzsprung-Russell diagram. How is the star changing?

It is getting larger and cooler.

Why do white dwarfs have very low luminosities?

They are very small.

In a Hertzsprung-Russell diagram, where are 90 percent of all the stars found?

on the main sequence

Where are red giant stars found in the Hertzsprung-Russell diagram?

above the main sequence

When compared to stars near the middle of the diagram, how are stars in the upper right part of the Hertzsprung-Russell diagram different?

They are always larger.

Use the Hertzsprung-Russell diagram to answer the following question: Which star in the diagram is most like the Sun?

HR 5337

Use the Hertzsprung-Russell diagram to answer the following question: Which star in the diagram has the highest surface temperature?

Alnilam

What property do most of the (apparently) bright stars in the sky share?

They are very luminous.

What property do most of the nearest stars in the sky share?

They are red dwarfs.

What type of stars are the most common?

lower (less luminous) main-sequence stars

Which of the following is most similar in size to a brown dwarf?

the planet Jupiter

Which of the following statements is true?
Red giants are hotter than very massive stars.
White dwarfs are readily visible by naked eye.
Massive stars consume fuel rapidly.
Low mass stars consume fuel rapidly.

Massive stars consume fuel rapidly.

What characteristic of a star primarily determines its location on the main sequence?

Mass

As a star exhausts the hydrogen in its core, how does its appearance change?

It becomes redder and more luminous.

Which of the following statements best describes why stars eventually die?

They exhaust all their fuel.

Why are star clusters important to our study of stars?

because they allow us to test our theories and models of stellar evolution

What property is the same for all stars in a star cluster?

age

What does the Chandrasekhar limit tell us?

White dwarfs more massive than 1.4 solar masses are not stable.

What is the ultimate fate of our Sun?

It will become a white dwarf.

In the year 1054 CE, Chinese astronomers observed the appearance of a new star. What occupies that location now?

a supernova remnant with a pulsar in the centre

If you were to land on a neutron star, how would your weight change relative to your weight on the Earth?

It would increase a lot.

What has greater density than a white dwarf?

a neutron star

Where is the singularity of a black hole found?

It is located within the event horizon.

What is the Schwarzschild radius?

the distance between the centre of a black hole and its event horizon

Which of the following factors does the escape velocity from the surface of an object depend on?

the object's mass and radius

You are asked to calculate the escape velocity for a white dwarf. What information do you need in order to complete your calculation?

the object's mass and radius

What would happen to Earth if the Sun were replaced by a 1-solar-mass black hole?

It would remain in its current orbit.

Which object has a shape that is most similar to the shape of a black hole?

a basketball

Which of the following lists objects in order of increasing size?
a solar-mass black hole, Earth, a neutron star
Earth, a solar-mass black hole, a neutron star
Earth, a neutron star, a solar-mass black hole
a solar-mass black hole, a neutron star, Earth

a solar-mass black hole, a neutron star, Earth

What is the term for the distance from the centre of a black hole at which the escape velocity is equal to the speed of light?

Schwarzschild radius

You are in a ship that orbits a black hole at a large distance and have a clock that flashes light every second. You throw the clock toward the black hole and record the time when you see each flash of light. What do your records show?

The time between flashes increases as the clock approaches the event horizon.

Which of the following is an example of time dilation?

As a star approaches a black hole's event horizon, it appears to move more and more slowly.

Which technique was used to capture the first-ever image of a black hole?

interferometry

If you know the apparent brightness of a star and its intrinsic brightness you can easily find its ....

distance

Where are stars born?

dense molecular clouds

What force is responsible for the collapse of an interstellar cloud?

gravity

As a star begins to form, what is its primary energy source?

gravitational potential energy

Under what conditions might interstellar gas clouds collapse to form stars?

if they encounter a shock wave

Why is the presence of massive stars in the Orion Nebula an indication that star formation is currently occurring?

Massive stars have short lives, so they must have formed recently.