Astronomy: Star Classification and H-R Diagram

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Questions and Answers

Which star listed has the lowest temperature?

α For

o Cet (correct)

35 Ari

γ Tri

Which star listed has the highest temperature based on their spectral type?

o Cet

γ Tri

ξ Per (correct)

α For

What is the correct order of star colors with increasing temperature?

Red, Blue, Yellow

Red, Yellow, Blue (correct)

Yellow, Red, Blue

Blue, Red, Yellow

What does the Doppler effect demonstrate concerning the motion of an object?

Shift the wavelength of spectral lines Signup and view all the answers

Which of the following spectral classifications represents the hottest star?

B5 Signup and view all the answers

Under what condition may interstellar gas clouds collapse to form stars?

They encounter a shock wave Signup and view all the answers

What happens to the pitch of a train's horn as it approaches?

The pitch gets higher Signup and view all the answers

What is indicated by the main sequence in an HR diagram?

Locations of stars in stable hydrogen fusion Signup and view all the answers

What is the primary energy source for a star while on the main sequence?

Nuclear fusion Signup and view all the answers

Why can't the lowest-mass stars become giants?

They cannot heat their centers hot enough Signup and view all the answers

What is a planetary nebula?

The expelled outer envelope of a medium mass star Signup and view all the answers

What does the Chandrasekhar limit refer to regarding white dwarfs?

White dwarfs must contain more than 1.4 solar masses Signup and view all the answers

The energy emitted by a white dwarf is characterized as what?

Not replaced Signup and view all the answers

What triggers a Type I supernova?

Exceeding the Chandrasekhar limit Signup and view all the answers

Which star is almost always associated with a nova?

A white dwarf in a close binary system Signup and view all the answers

What happens as material leaves an expanding star and begins to fall into a white dwarf?

An accretion disk will form around the white dwarf Signup and view all the answers

What causes the material accreting onto a neutron star or black hole to emit x-rays?

The material becomes hot enough that it radiates primarily at x-ray wavelengths. Signup and view all the answers

Which statement about the experience of material flowing into a black hole is correct?

The material will increase in mass. Signup and view all the answers

How is a black hole best conceptualized?

A massive body of infinitely small size. Signup and view all the answers

Where is the singularity of a black hole located?

At the center of the event horizon. Signup and view all the answers

What is the escape velocity at the event horizon around a black hole?

Larger than the speed of light. Signup and view all the answers

What will happen to a white dwarf as it evolves?

It will produce a type-II supernova. Signup and view all the answers

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

Iron fusion releases energy rather than consuming it. Signup and view all the answers

What is the last stage of nuclear fusion for a star similar to our Sun?

Hydrogen to helium. Signup and view all the answers

What typically occurs after a giant star phase in stellar evolution?

It becomes a white dwarf. Signup and view all the answers

Where are elements heavier than iron predominantly created?

Supernovae. Signup and view all the answers

What does a supernova explosion typically leave behind?

A shell of gas. Signup and view all the answers

What is the density of a neutron star comparable to?

That of an atomic nucleus. Signup and view all the answers

What happens to stars that have expelled a planetary nebula?

They become white dwarfs. Signup and view all the answers

Which labeled location on the HR diagram indicates a luminosity and temperature similar to that of a T Tauri star?

Location 4 Signup and view all the answers

What can initiate the free-fall contraction of a molecular cloud?

Shock waves from supernovae Signup and view all the answers

Why does the proton-proton chain require high temperatures?

To overcome the Coulomb barrier Signup and view all the answers

Which fusion cycle occurs in the cores of massive stars on the main sequence?

The CNO cycle Signup and view all the answers

At what minimum temperature must the center of the sun reach for energy production by the proton-proton chain?

$10^7$ K Signup and view all the answers

What characterizes the carbon-nitrogen-oxygen cycle?

Combines four hydrogen nuclei to form one helium nucleus Signup and view all the answers

What occurs in the region of the sun just below the photosphere?

Undergoing thermonuclear fusion using the CNO cycle Signup and view all the answers

What is the primary result of the reaction in the carbon-nitrogen-oxygen cycle?

The production of energy Signup and view all the answers

Why do neutron stars spin rapidly?

They conserved angular momentum when they collapsed. Signup and view all the answers

What makes neutron stars difficult to locate despite their high temperatures?

They have small surface areas. Signup and view all the answers

What does the fusion of electrons with protons at high densities produce?

Degenerate electrons. Signup and view all the answers

Which statement about the density of neutron stars and pulsars is correct?

A neutron star is denser than a pulsar. Signup and view all the answers

What are the necessary conditions for a neutron star to be classified as a pulsar?

It must rotate on an axis that differs from its magnetic field's axis. Signup and view all the answers

What is the nature of the event horizon of a black hole?

It has a radius equal to the Schwarzschild radius. Signup and view all the answers

Why is an isolated black hole difficult to detect?

Very little matter would be falling into it. Signup and view all the answers

What is a primary method in the search for black holes?

Finding x-ray binaries with massive compact companions. Signup and view all the answers

Study Notes

Multiple Choice Questions

Giant stars are larger in diameter than the Sun because they are more luminous but have similar temperatures.
Giant stars are more luminous than the Sun, larger in diameter, cooler than B-type stars, and located above the main sequence in the H-R diagram.
The Sun is most like the star Arcturus in the provided H-R diagram.
The star Alnilam in the diagram has the highest surface temperature.
The star Antares in the diagram has the largest radius.
Stars with the smallest radius are in the lower left corner of the H-R diagram.
Spectroscopy and eclipse observations of eclipsing binary stars allow astronomers to calculate both their masses and sizes of individual stars.
Doppler shift observations of spectroscopic binary stars allow astronomers to calculate their masses.
Binary stars can be detected by observing them as two separate stars, noting a wiggly proper motion of one star, observing one star dimming as another passes in front of it, or by observing pairs of absorption lines in the spectrum of what appears to be a single star.
The mass of a visual binary star pair can be obtained from the time it takes the stars to orbit each other, and their orbital size.
The white dwarf star Sirius B has a mass comparable to the Sun because it is part of a binary star system with Sirius A.
Ninety percent of stars are on the main sequence in the H-R diagram.
The most common type of star is a lower main sequence star.
If two stars have the same luminosity, the farther star will appear dimmer.
Some stars appear to move back and forth against the background stars due to the Earth's orbital motion.
Stars in the upper-right of the Hertzsprung-Russell diagram are cooler and larger in size compared to stars in the middle of the diagram.
When a train approaches, the pitch of the horn will be higher than when it moves away.
The star with the lowest temperature is o Cet.
The star with the highest temperature, according to the spectral type, is o Cet.
The order of star colors in increasing temperature is: red, yellow, blue.
The Doppler effect relates the motion of any object to the shift in wavelength of its spectral lines.
The hottest stars, by spectral classification, are B-type stars.
Interstellar gas clouds might collapse into stars if they encounter a shockwave.
A T Tauri star is similar in luminosity and temperature to location 1 on the HR diagram.
The free-fall contraction of a molecular cloud can be initiated by shock waves from supernovae.
The proton-proton chain needs high temperature because protons must overcome the Coulomb barrier.
The CNO cycle is the thermonuclear fusion of hydrogen into helium occurring in the cores of massive stars on the main sequence.
The center of the Sun must have a temperature of at least 10 million Kelvin.
The carbon-nitrogen-oxygen cycle involves a slightly lower temperature than the proton-proton chain.
The region just below the photosphere in the Sun transfers energy through convection to the photosphere.
In massive stars, the central cores transmit outward energy through convection while less massive stars transmit energy through radiation.
Stars on the main sequence derive their energy primarily from nuclear fusion.
The initial energy source for the formation of a star is gravitational potential energy.
The lowest-mass stars don't become giants because they cannot heat their centers hot enough.
A planetary nebula is the expelled outer envelope of a medium mass star.
The Chandrasekhar limit is a measure of the largest possible mass of a white dwarf star.
A Type I supernova occurs when a white dwarf exceeds the Chandrasekhar Limit.
A nova is an outburst of energy from a white dwarf in a close binary system, involving hydrogen fusion.
Material accretes onto a neutron star or black hole, emitting X-rays due to synchrotron radiation, hydrogen fusion or the conversion of thermal energy into gravitational energy. Material falling into a black hole increases in mass and experiences time dilation.
Singularities are located at the center of a black hole's event horizon. A black hole is a region of spacetime with gravitational pull so strong that nothing, not even light, can escape. The escape velocity at the event horizon of a black hole is larger than the speed of light.

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Description

Test your understanding of giant stars, the H-R diagram, and binary star systems. This quiz covers key concepts in stellar classification and the methods astronomers use to study stars. Ideal for students of astronomy and astrophysics.