ASTRO UNIT 3 - Stars

What is the approximate range of masses that newborn main-sequence stars can have? 0.1 to 1,000 solar masses 0.1 to 150 solar masses 0.001 to 150 solar masses 0.1 to 10 solar masses 0.001 to 10 solar masses

0.1 to 150 solar masses The lower limit is 0.08 solar masses. Below that, the core is not hot enough to sustain nuclear fusion. The upper limit of around 150 solar masses is due to the fact that higher mass objects would be so luminous that they would blow themselves apart with their own radiation pressure. Return to Assignment

Consider the six stages labeled on (Figure 1) at left, showing the life track of a one-solar-mass star. During which of the labeled stages is the star generating energy through hydrogen fusion in its central core? 123456

1 Stage 1 is the star's hydrogen-fusing, main-sequence stage.

At which of the first five labeled stages is the star in hydrostatic equilibrium (when gravity inward is balance by outward pressure from fusion)?

1, 4 The star is in energy balance when its core energy production matches the amount of energy it radiates into space. As explained in the video, this is true only when the star is a main-sequence star with hydrogen core fusion and when it is a helium core-fusion star. It is out of energy balance at all other times, which is why it is either contracting or expanding.

Approximately what core temperature is required before hydrogen fusion can begin in a star? 10,000 K 10 million K 10 billion K 1 billion K 10 trillion K

10 million K

Which of the following stars would have the shortest Main Sequence lifetime? (All masses are given in Solar masses) 10 solar masses 5 solar masses They all would have the same length of main sequence lifetime. 1 solar mass

10 solar masses

What is the approximate temperature of the Sun's core?

15 million K

During which of the labeled stages on (Figure 1) at left, is the star generating energy through helium fusion in its central core (along with hydrogen fusion in a surrounding shell)?

4 Stage 4 is the star's helium core-fusion stage, when it generates energy both from helium fusion in the central core and hydrogen fusion in a surrounding shell.

The star expels its outer layers into space almost immediately upon the end of Stage _____.

5 During Stage 5 the star has an inert carbon core surrounded by shells of helium and hydrogen fusion. Because the core will never become hot enough for carbon fusion, this is the last stage of the star's life, and at the end of this stage it expels its outer layers as a planetary nebula.

Approximately, what is the Sun made of (by mass)? 50% hydrogen, 25% helium, 25% other elements 100% hydrogen and helium 90% dark matter, 10% ordinary matter 70% hydrogen, 28% helium, 2% other elements

70% hydrogen, 28% helium, 2% other elements

Study this H-R diagram. What is the spectral type of the star Sirius? (The red arrow helps you locate Sirius on the diagram.) 10^2 Main sequence A blue

A Spectral type is shown along the horizontal axis of the H-R diagram, and you can see that Sirius has spectral type A.

Which star takes the longest time to become a main sequence star? A 1 solar mass star A 3 solar mass star A 5 solar mass star A 2 solar mass star A 4 solar mass star

A 1 solar mass star Lower mass stars take longer in all phases of life.

What is a protostar? A star that is still in the process of forming A star in its final stage of life An intermediate-mass star A star that has planets

A star that is still in the process of forming It generates energy by gravitational contraction, as it is not yet hot enough for nuclear fusion it its core.

Five stars are shown on the following H-R diagrams. Rank the stars based on their surface temperature from highest to lowest. If two (or more) stars have the same surface temperature, drag one star on top of the other(s).

All five stars appear at the same place along the horizontal axis showing spectral type. Because spectral type is related to surface temperature, all five stars must have the same surface temperature. Now proceed to Part C to determine how these stars vary in luminosity.

Study this H-R diagram. Which of the following stars is the largest in size (radius)? (The red arrows help you locate these stars on the diagram.) Aldebaran Antares Canopus Alpha Centauri B

Antares Radius increases diagonally from lower left to upper right, and Antares is the farthest toward the upper right.

Using the above table, determine which of the stars in the answers has the coolest surface temperature. (See the hint if you are color blind) Procyon Anatares Rigel Capella

Antares (most red)

Study this H-R diagram. Which of the following stars is the most massive? (The red arrows help you locate these stars on the diagram.) Vega Beta Centauri DX Cancri Bellatrix

Beta Centauri Beta Centauri is highest up along the main sequence, which means it is the most massive.

Suppose the star Betelgeuse (the upper left shoulder of Orion) were to go 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.

We use the term "dwarf" to refer to a smaller sized star or star-like object. Which of the following refers to a star-like object that was not massive enough that the core reached temperatures for Hydrogen fusion? Red dwarf White dwarf Brown dwarf

Brown dwarf

In which of the following layer(s) of the Sun does nuclear fusion occur? photosphere convection zone radiation zone core chromosphere corona

Core Nuclear fusion occurs only in the core of the Sun, where the temperatures, pressures, and densities are highest. Return to Assignment

Which of the following makes it possible for us to observe stellar parallax (from Earth)? Earth's orbit around the Sun the gradual change in the patterns of the constellations over thousands of years the varying speed of Earth in its orbit around the Sun the gradual motion of stars in the local solar neighborhood

Earth's orbit around the Sun Stellar parallax occurs because we see stars from different vantage points as Earth orbits the Sun. As shown in the video, this causes the positions of relatively nearby stars to appear to shift over the course of each year (compared to the positions of more distant objects).

All stars are about the same radius as the Sun. True False

False

All stars have the same mass as the sun. False True

False

No visible light can escape a black hole, but things such as gamma rays, X-rays, and neutrinos can. True False

False

The apparent brightness of a star depends only on its luminosity. True False

False

Two stars have the same luminosity. Star X is spectral type F, while Star Y is spectral type K. Star X must be larger in radius than Star Y. True False

False

We can measure the parallax of most stars in our galaxy. True False

False

We use Spectral Type (letter and number) and Luminosity class (roman numeral) to labe stars. These three characters end up infering a lot of information about stars. What is the notation for the sun? (type all three together with no spaces for grading purposes).

G2V

What is the arrow pointing to? This is a feature visible in the photosphere.

Granule Hot gas is rising up from the solar interior. The bubbling pattern is caused by the underlying convection, and the bright spots are where hot gas is bubbling upward.

Which force of nature causes nebula to collapse Star Gravity Electric Magnetic Strong

Gravity

When a star leaves the Main Sequence, what element dominates the core? Carbon Iron Hydrogen Helium

Helium

Listed following are characteristics that describe either high-mass or low-mass stars. Match these characteristics to the appropriate category.

High-Mass Stars (>8 Msun) end life as a supernova do fusion faster during main sequence life late in life fuse carbon into heavier elements Low-Mass Stars (<2 Msun) have longer lifetimes end life as a planetary nebula the Sun is an example final corpse is a white dwarf A long-lived star such as the Sun eventually ejects its outer layers as a planetary nebula, leaving behind a white dwarf.

You learned about the general concept of parallax in Chapter 2, and the video offers a review of the basic ideas. To check your understanding of the concept, which of the following is a valid way of demonstrating parallax for yourself? Hold up your hand in front of your face, and alternately close your left and right eyes. Get a camera, and photograph a person who is running back and forth. Look up at a star, and notice how it moves toward the western horizon during the night. Hold up your hand in front of your face, and move it slowly back and forth.

Hold up your hand in front of your face, and alternately close your left and right eyes. The key point is that parallax is an apparent shift in an object's position caused by a change in how you view it, not an actual motion of the object.

Why does a star grow larger immediately after it exhausts its core hydrogen? The internal radiation generated by the hydrogen fusion in the core has heated the outer layers enough that they can expand after the star is no longer fusing hydrogen. The outer layers of the star are no longer gravitationally attracted to the core. Helium fusion in the core generates enough thermal pressure to push the upper layers outward. Helium fusion in a shell outside the core generates enough thermal pressure to push the upper layers outward. Hydrogen fusion in a shell outside the core generates enough thermal pressure to push the upper layers outward

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

Which of the following luminosity classes refers to Red Giants?

III

Which part of the electromagnetic spectrum generally gives us our best views of stars forming in dusty clouds? Ultraviolet Blue light Visible light Infrared

Infrared Infrared light can pass through dusty clouds, unlike visible light.

This star map shows stars as we see them in our sky from Earth, centered around the constellation Canis Major. Larger dots represent brighter stars, and a few of the brightest stars are identified. From this view alone, what can you conclude about Sirius? It has the greatest apparent brightness of any star in this region of the sky. It is the nearest star in this region of the sky. It is the most luminous star in this region of the sky. It is actually a binary star system in which the second star is a white dwarf. All of the answers are true

It has the greatest apparent brightness of any star in this region of the sky.

What happens to the temperature of the collapsing nebula? Nothing It increases It decrease

It increases

Why can the fusion of carbon occur in high-mass stars but not in low-mass stars?

It is because the cores of low-mass stars never get hot enough for carbon fusion.

Mark all the reasons a star might look bright from the Earth? It is bright It is faint It is close It is far away

It is bright It is close

You observe a red giant star. What is happening to that star? It is stable in its size, and is fusing hydrogen in its core. It is decreasing in size, and is fusing hydrogen in a shell around its core. It is increasing in size, and is fusing hydrogen in its core. It is increasing in size, and is fusing hydrogen in a shell around its core.

It is increasing in size, and is fusing hydrogen in a shell around its core.

Five stars are shown on the following H-R diagrams; notice that these are the same five stars shown in Part B. Rank the stars based on their luminosity from highest to lowest. If two (or more) stars have the same luminosity, drag one star on top of the other(s).

Luminosity is shown along the vertical axis, with stars higher up more luminous than those lower down. Note that each tickmark along the luminosity axis represents a change by a factor of 10 from the prior tickmark, so the range of luminosities is quite large. Continue to Parts D and E to investigate surface temperature and luminosity for a different set of five stars.

Stars are formed in giant molecular clouds which are a type of ... Nebula Solar System Star Cluster galaxy globular cluster

Nebula

How are elements beyond iron formed in massive-star supernovae? Neutrons are captured into the nuclei then change into protons creating the higher elements protons are captured into the nuclei to create the higher elements Iron fusion creates the higher elements

Neutrons are captured into the nuclei then change into protons creating the higher elements

What layer of the Sun are we seeing in this photo?

Photosphere; The photosphere is the visible surface of the Sun.

Which of the stars below would be considered a Red Giant? Rigel DX Cancri Pollux Procyon

Pollux

What is the name of the closest star outside the solar system? (spell it correctly)

Proxima Centauri Submit

Using the above table, determine which of the stars in the answers has the hottest surface temperature. (See the hint if you are color blind) Rigel Anatares Capella Procyon

Rigel

Sirius is a star with spectral type A and Rigel is a star with spectral type B. What can we conclude? Sirius has a higher core temperature than Rigel. Rigel has a higher core temperature than Sirius. Sirius has a higher surface temperature than Rigel. Rigel has a higher surface temperature than Sirius.

Rigel has a higher surface temperature than Sirius.

Sirius has M=1.46 and m= − 1.43 (note a minus sign here) Betelgeuse has M= − 5.01 and m=0.157 (note there is a minus sign in front of the 5) Mark all of the following that are true statements. Sirius is the actual brighter star (more luminous) Betelgeuse looks brighter in the sky Sirius looks brighter in the sky Betelgeuse is the actual brighter (more luminous) stars

Sirius looks brighter in the sky Betelgeuse is the actual brighter (more luminous) stars

Which statement accurately describes the length of Stage 1 compared to Stages 2 through 5? (Ignore Stage 6 for this question.)

Stage 1 lasts nearly 10 times as long as Stages 2 through 5 combined. A one-solar-mass star has a main-sequence lifetime (Stage 1) of about 10 billion years, while the rest of the stages combined last only about 1 billion years.

This X-ray image shows a loop of hot gas above the surface of the Sun. If we took a visible light photo that looked in the Sun's photosphere just under the two points where the loop of gas comes down (arrows), what would we find?

Sunspots

Study this figure and its axis labels. What is this graph showing us?

The number of sunspots on the Sun tends to increase and decrease with an approximately 11-year cycle.

What do sunspots, solar prominences, and solar flares all have in common?

They are all strongly influenced by magnetic fields on the Sun.

If your spaceship flew within a few thousand kilometers above the event horizon, you and your ship would be rapidly sucked into it.

This statement does not make sense. A circular orbit, even at a distance of a few thousand kilometers above the event horizon is perfectly stable. If you use the engines of the spaceship to put it on such orbit, the spaceship will not be sucked into the black hole.

The spectral type, surface temperature, and color of a star are all related. True False

True

Two stars both lie on the main sequence. Star X is spectral type A, while Star Y is spectral type G. Star X must be more massive than Star Y. True False

True

Which of these stars has the coolest surface temperature? an A star an F star a K star

a K star

Consider the four stars shown following. Rank the stars based on their surface temperature from highest to lowest.

a blue dwarf star sun an orange main-sequence star a red supergiant Notice that temperature is related to color, and follows the order of the colors in the rainbow: Blue (or violet) stars are the hottest, while red stars are the coolest. In the parts that follow, the H-R diagrams show the correlation between color and temperature on the horizontal axis.

Which of these stars has the hottest core? a blue main-sequence star a red supergiant a red main-sequence star

a red supergiant

A typical neutron star is more massive than our Sun and about the size (radius) of _________. Earth Jupiter the Moon a small asteroid (10 km in diameter)

a small asteroid (10 km in diameter)

All stars on the main sequence (mark all that apply) are the same age are all doing helium fusion in their cores are all doing hydrogen fusion in their cores have the same surface temperature have the same mass

are all doing hydrogen fusion in their cores

The ultimate fate of our Sun is to ________.

become a white dwarf that will slowly cool with time

When a massive star goes supernova and the core left behind has a mass of 5 solar masses, what type of object must it be?

black hole

Star A is identical in all ways to Star B, except that Star A is twice as far from us as Star B. Therefore, ________. both stars have the same luminosity, but the apparent magnitude of Star B is fainter than that of Star A both stars have the same luminosity, but the apparent magnitude of Star B is brighter than that of Star A both stars have the same apparent magnitude, but the luminosity of Star B is four times that of Star A

both stars have the same luminosity, but the apparent magnitude of Star B is brighter than that of Star A

What element(s) should you expect to be most abundant in the star when it reaches Stage 6? both hydrogen and helium iron helium hydrogen carbon

carbon At Stage 6 the star has become a white dwarf, which is essentially the leftover core after all fusion has ceased. Because the last stage of fusion was helium fusion, in which helium fuses to make carbon, the white dwarf should be composed largely of carbon. (Some oxygen can also be produced during the late stages of helium fusion, so white dwarfs are often made of both carbon and oxygen.)

Stars can form most easily in clouds that are cold and dense warm and dense hot and low-density

cold and dense

The following figures show various stages during the life of a star with the same mass as the Sun. Rank the stages based on when they occur, from first to last.

contracting cloud of gas and dust protostar main sequence G star red giant planetary nebula white dwarf Remember that these stages take very different amounts of time. A one-solar-mass star spends about ten billion years as a hydrogen-burning main-sequence star, making this by far the longest stage of its life.

Provided following are various stages during the life of a high-mass star. Rank the stages based on when they occur, from first to last.

contracting cloud of gas and dust protostar main sequence O star red supergiant supernova neutron star Remember also that high-mass stars progress through all these stages at a much faster rate than lower-mass stars. The highest-mass stars may be born, live, and die in only a few million years. Note also that while this particular high-mass star leaves behind a neutron star after its supernova, an even higher-mass star may instead leave behind a black hole.

Compared to the star it evolved from, a red giant is cooler and dimmer. hotter and brighter. cooler and brighter. hotter and dimmer. the same temperature and brightness.

cooler and brighter.

What layer of the sun is shown here in x-ray wavelengths? It is the outermost layer of the sun.

corona You can tell it is the coronal because it extends so far out; the corona emits most strongly in X-rays, so that's how you know it is an X-ray image.

Listed following are the different layers of the Sun. Rank these layers based on their distance from the Sun's center, from greatest to least.

corona chromosphere photosphere convection zone radiation zone core

The sketch above shows groups of stars on the H-R diagram, labeled (a) through (e); note that (a) represents the entire main sequence while (c) and (d) represent only small parts of the main sequence. Which group most closely represents Red Giants

e (upper mid-right circle)

After a massive-star supernova, what is left behind?

either a neutron star or a black hole

Stars with high masses live longer than stars with lower masses. true false

false

The heaviest element produced by stars or in supernovae is silicon. true or false

false

What is a planetary nebula?

gas ejected from a star in the final stage of its life

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

hotter and dimmer

What does the apparent magnitude of a star tell us about that star? how bright it appears from Earth its mass its radius how much energy it is emitting

how bright it appears from Earth

New stars are formed from free space, out of pure energy in galactic centers by the black hole within supernova remnants in huge, cool dust and gas clouds

in huge, cool dust and gas clouds

Where on this diagram do we find stars that are hot and dim? in the upper left hand corner in the upper right hand corner in the lower left hand corner in the lower right hand corner

in the lower left hand corner

Where on this diagram do we find stars that are cool and dim? in the upper left hand corner in the upper right hand corner in the lower left hand corner in the lower right hand corner

in the lower right hand corner

Where on this diagram do we find stars that are hot and luminous? in the upper left hand corner in the upper right hand corner in the lower left hand corner in the lower right hand corner

in the upper left hand corner

Where on this diagram do we find stars that are cool and luminous? in the upper left-hand corner in the upper right hand corner in the lower left hand corner in the lower right hand corner

in the upper right hand corner

What happens to the core of a high-mass star after it runs out of hydrogen?

it shrinks and heats up

In order to predict whether a star will eventually fuse oxygen into heavier elements in its core, you need to know what fact about the star?

its mass

Follow the supernova explosion of a massive star, the core has a mass of 1.8 solar masses. Which type of remnant is it? white dwarf neutron star black hole

neutron star

The source of energy that keeps the Sun shining today is ________.

nuclear fusion

What are the two sources of energy for the forces that either balance or don't inside a star?

nuclear fusion and gravitational contraction

The Sun's surface is called the ________.

photosphere

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 Submit

During which of the following phases of life is a star's pressure and gravity out of equilibrium? white dwarf helium core fusion red giant main sequence

red giant

What is the name of the brightest star in the nighttime sky?

sirius

Compared to a nearer star, a more distant star will have a __________. smaller parallax angle parallax shift taking less time to go back and forth parallax shift taking more time to go back and forth larger parallax angle

smaller parallax angle To summarize: Tthe greater a star's distance, the smaller its parallax angle.

What types of stars end their lives with supernovae? stars that have reached an age of 10 billion years all stars that are yellow in color stars that are similar in mass to the Sunall stars that are red in color stars that are more massive than eight times the mass of the Sun

stars that are more massive than eight times the mass of the Sun

The dark spots in this photo (such as the one indicated by the arrow) represent what we call _____________.

sunspots

The interstellar clouds called molecular clouds are _________. the cool clouds in which stars form the clouds in which elements such as carbon, nitrogen, and oxygen are made clouds that are made mostly of complex molecules such as carbon dioxide and sulfur dioxide the hot clouds of gas expelled by dying stars

the clouds in which elements such as carbon, nitrogen, and oxygen are made They are called "molecular" clouds because they are cold enough to allow their hydrogen atoms to pair up into hydrogen molecules (H2).

What happens when a main-sequence star exhausts its core hydrogen fuel supply? The core shrinks while the rest of the star expands. The entire star shrinks in size. The core immediately begins to fuse its helium into carbon. The star becomes a neutron star.

the core shrinks while the rest of the star expands

Which of the following is closest in size (radius) to a white dwarf?

the earth

Stars with masses greater than 8 solar masses with all end their lives with a supernova explosion. true false

true