Astronomy Part 4 Reading Assignments

Possible masses of stars are given, in solar masses. Match these to indicate if the masses are typical, unexpected, or impossible.

0.01-impossible 100-very uncommon 2-normal 0.5-normal and more common than the Sun 25-uncommon but normal

The mass lost by the Sun from its solar wind during its 10 billion year life will be about ____% of its total mass.

0.02

From theoretical studies, astrophysicists have determined that stars can only range in mass from a fairly firm lower limit of ______ M☉ to an upper limit of about ______ M☉, although stars more massive than 30 M☉ are rare. (Select two answers.)

0.08 300

Match the values to the appropriate descriptions about the masses of stars.

0.08 M☉-About the lowest possible mass 0.2 M☉-A mass at the lower end of what is common 20 M☉-A somewhat rare high-mass star 300 M☉-About the highest mass possible 0.016 M☉-Something with this mass can't be a star. 10 M☉-An uncommon mass, but not rare.

Select all the possible combinations of stars in a binary star system in which the period is 3 years and the semi-major axis is 3 AU.

1 M☉ and 2 M☉ 0.5 M☉ and 2.5 M☉

Match the labels to the missing elements describing the products of shell fusion in a massive star's core.

1- Helium 2- Carbon 3- Silicon 4- Iron

Rank these stars clusters' ages from youngest (top) to oldest (bottom) based on the descriptions of what types of stars in them are still on the main sequence.

1. A cluster with blue-white stars on the MS 2. A cluster with stars a little hotter than the Sun on the MS 3. A cluster with yellow stars like the Sun on the MS 4. A cluster with cool red stars on the MS

In visible light, planetary nebulae are some of the most beautiful celestial objects in our Galaxy. A simulation of the geometry is shown in the figure. Arrange the steps to describe why these object glow.

1. A dying low-mass star ejects its outer layers as a stellar wind which travel out well outside any exoplanetary solar systems. 2. The young white dwarf at the center emits significant ultraviolet radiation. 3. The UV rays travel out until they are absorbed by the expelled gas, exciting electrons in nitrogen, oxygen, and hydrogen atoms in the expelled gas. 4. When the excited electrons drop down, they take multiple steps, emitting lower-wavelength red, green, yellow and blue photons.

The inverse-square law for light is B = L/4πd^2. Order the steps to show how you would calculate the relative distances of two standard candles if star A is 16 times brighter than B.

1. A is 16 times brighter than B, but 2. A and B have the same L, so 3. B x d^2 must be constant. If B is 16 times more for one star, d^2 must be 16 times more for the other; therefore, 4. d must be √16=4 times more, and 5. since A is brighter than B, it must be the closer star. B must be four times farther away.

Rank the binaries by how close their center of mass would be to the halfway point between the stars. Put the one closest to halfway at the top and the one farthest from halfway at the bottom.

1. A pair of 2 M yellow stars 2. 3 M red giant and a 2 M black hole 3. 2 M yellow star and a 1 M white dwarf 4. 9 M white B star and a 3 M neutron star 5. 1 M yellow star and a 5 M blue giant

All of the objects below have magnetic fields. Arrange them by how strong you expect their magnetic fields to be, from the strongest (top) to the weakest (bottom).

1. A pulsar 2. The Sun 3. Jupiter 4. Earth

Rank the stars according to their size (radius) with the largest at the top.

1. A star found in the upper right of the HR diagram 2. A blue main-sequence star 3. The Sun 4. A star in the lower tight of the HR diagram 5. A white dwarf with a surface temperature of 20,000 K

Arrange the steps to describe how a nova occurs.

1. A white dwarf is a binary with a giant or main sequence star. he orbits are so close that the companion star fills its Roche lobe. 2. Hyrdrogen flows out of the lobe toward the white dwarf, forming an accretion disk. 3. Heated as it rotates and falls, hydrogen builds up on the surface of the star, increasing in density as more collects on top. 4. Pushed to high enough density and temperature to fuse, the entire layer of hydrogen explodes in a thermonuclear blast (the nova). 5. In the blast, the luminosity increases by 10^4 or 10^5 and the fusing layer is ejected in an expanding shell.

Rank these nearby stars in order of increasing luminosity (top to bottom). Absolute magnitudes are given by M and apparent magnitudes by m.

1. Barnard's Star 2. Procyon 3. a Centauri 4. Sun 5. Sirius

Rank the following stars by luminosity from the most luminous (top) to the least luminous (bottom).

1. Betelgeuse 2. Sirius 3. The Sun 4. Procyon

Astronomers observe a white dwarf and an aging companion star. Place the following events describing a Type Ia supernova in the correct order.

1. Gas from the companion star accumulates on the surface of the white dwarf. 2. The mass of the white dwarf exceeds the Chandrasekhar limit. 3. Carbon and oxygen begin fusing to form silicon. 4. Silicon begins fusing to form nickel. 5. The energy released by fusion blows the white dwarf apart.

Order the stages of a low-mass star's life from the beginning (top) to the end (bottom).

1. Interstellar Cloud 2. Main Sequence 3. Red Giant 4. Planetary Nebula 5. White Dwarf

Arrange the following stages of a high-mass star in order of when they occur. Put the earliest stage at the top.

1. Interstellar cloud 2. Main-sequence star 3. Re giant 4. Neutron Star

Rank the following stars from hottest (top) to coolest (bottom).

1. Iota Orionis 2. Spica 3. Mizar 4. Caph 5. Arcturus 6. Betelgeuse

Arrange the following fusion products in order of the temperature required to create them, from hottest (top) to coolest (bottom).

1. Iron 2. Silicon 3. Oxygen 4. Helium

Arrange the variable stars based on their pulsation periods, from the longest (top) to the shortest (bottom).

1. Mira 2. Cepheids 3. RR Lyrae

Rank the proposed energy sources with how long each could keep the Sun hot. Place the shortest-lived source of energy at the bottom.

1. Nuclear fusion 2. Gravity 3. Coal

Arrange the statements to describe pulsation in giant stars.

1. Radiation gets trapped by the upper layers. 2. As a result, the pressure and temperature increase. 3. The star expands. 4. Radiation excapes and the star cools, then shrinks.

Arrange the steps in order to explain how the Sun's magnetic field heats the solar atmosphere. (Place the first step at the top.)

1. Rising pockets of gas shake the magnetic field. 2. Waves are formed at the photosphere. 3. Waves begin to move up through less-dense chromosphere and corona. 4. Ub tge kess-dense gas, the waves make gas particles move faster. 5. Particles move faster, and hence the gas is hotter.

Arrange the events to describe how a supernova occurs in a massive star.

1. Si atoms are fused in the core to form iron. 2. After a day or so, the silicon fuel is used up. The core contracts, heating the iron atoms, but fusion of iron does not release energy. 3. Gravity finally overtakes outward gas pressure and core compresses. 4.Gravitational potential energy is used to break up iron nuclei, but the core is so compressed that protons and electrons merge and become neutrons. 5. The neutron core collapses until it reaches nuclear densities; the star's layers free fall and bounce off the degenerate neutron core. 6. Heated falling layers undergo explosive fusion, and momentum from impacting the core combine to cause a tremendous outward explosion.

Given their spectral classification, rank the following stars in order from hottest (top) to coolest (bottom).

1. Sirius, and A star 2. a G star 3. Aldebaran, a K star 4. Betelgeuse, an M star

Arrange the steps to explain the proton-proton chain. (Put the first at the top and the last at the bottom.)

1. Two protons (2p) fuse, creating a 2H nucleus (1p, 1n), a positron, and a neutrino. 2. Almost immediately, the positron annihilates with an electron, releasing energy. 3. One 2H nucleus (1p, 1n) fuses with a proton to form 3 He (2p, 1n) and release a gamma ray. 4. Two 3He nuclei fuse to form one 4He nucleus and release two protons that can start the chain.

If you were measuring the masses of white dwarf stars, you would expect the most massive ones to be about ______ M☉.

1.4

Below are methods to find the actual length of an AU in kilometers. Assuming you have the equipment needed and good models of planetary orbits, rank the methods based on how difficult it would be to make the necessary observations (think about when or how often you could make them). Put the easiest at the top and the hardest at the bottom.

1.Timing a radar signal bounced off another planet. 2.Triangulating the distance to Mars at closest approach 3.Measuring a transit of Venus

Select all the stars that would have the same luminosity. (Use the Stefan-Boltzmann law.) Presented are the radii and temperatures of five stars compared to the Sun.

1/2 R☉, 4 T☉ 2 R☉, 2 T☉ 8 R☉, T☉

An arc minute is ______. (Select all that apply.)

1/60 of a degree a unit of angular size

Regardless of mass, about ______ percent of a main sequence star's hydrogen is generally available for fusion.

10

Using the mass-luminosity relation, L ≈ M3.5, with values in solar units, about what would be the mass of a main-sequence star of luminosity 3000 L☉?

10 M☉

Match the length of time to the period of the Sun's evolution.

10 million years-Mira variable 10 billion years-Main sequence 1 billion years-Red giant 100 million years-Yellow giant 10,000 years-Planetary nebula

Compared to its time on the main sequence, how long will a star remain in the helium-fusing part of the H-R diagram?

10 to 20%

Two stars, a red giant and a blue supergiant, are the same size. If the temperature of the blue supergiant is 10 times the temperature of the red giant, how many times more luminous is the blue star?

10,000

You observe a blue star whose wavelength peaks at 290 nm (in the ultraviolet, in fact). According to Wien's law, what is its temperature?

10,000 K

A star with a parallax of 0.01 arc seconds would have a distance of ______.

100 parsecs (pc)

The Sun will eventually become a white dwarf. This white dwarf will have a diameter _____ the present-day Sun.

100 times smaller than

Alpha and Beta Centauri appear the same brightness in the image. However, Beta Centauri is about 100 times farther away than Alpha Centauri. This means that Beta Centauri must be ______ times as luminous as Alpha.

100^2 = 10,000

A type Ia supernova explosion, at its brightest, can produce nearly ______ times the Sun's luminosity.

10^10

Rigel has a temperature roughly twice that of the Sun, and a radius about 80 times larger. Accordingly, we expect Rigel's luminosity to be about ____ solar luminosities. (You can look Rigel up on an H-R diagram and check your result.)

10^5

The lifetime of a star is t = M/L × 10^10 years (with M and L in solar units). Reference the HR diagram and estimate the lifetime of Spica.

10^7 years

Solar activity and numbers of sunspots peak approximately every _____ years.

11

The Sun's magnetic field takes about 22 years to reverse twice--that is, for the north pole to become the north pole again. Therefore, the sunspot cycle peaks about once every ______ years.

11

The time between successive sunspot peaks is about _____ years.

11

Match the temperatures to the appropriate locations.

15 million K-The core of the Sun 100 million K-The core of a star fusing helium 5000 K-The surface of the Sun 10 K-Interstellar gas cloud 3000 K-The surface of a red giant 1500 K-The surface of a protostar

The overall polarity of the Sun's magnetic field reverses with each sunspot cycle. That is, every other cycle magnetic "north" is in the same side of the Sun. Using the graph of sunspot numbers, select all the maximums below with the same field polarity as in the peak of activity in 1960.

1908 1980 1870

Select all the equations that are important to understand fusion in the Sun.

1H + energy → n + e+ + ν 4 1H → 4He + energy + 2 ν E = m × c2

A convenient form of the Stefan-Boltzmann equation is shown. If a star has a luminosity of 64 L☉ and has a surface temperature of 2 T☉, we can expect its radius to be _____ R☉.

2 or two

If a low-mass M star has a luminosity of about 0.5 L☉, about how much energy does it produce per second?

2 × 1026 watts

Polaris has an apparent magnitude of 2, and the star (X) at the lower left of the bowl has a magnitude of 5. Based on the magnitude scale, you can say that Polaris is ______ times brighter.

2.512^3 ≈ 16

As seen in the diagram, Cepheid variable stars with a luminosity of about 10^4 L☉ have a period of approximately ______ days.(Use the number for the nearest tick mark.)

20

Over the main-sequence phase of its lifetime, a star's luminosity increases by a factor of about how much?

3

As seen in the diagram, Cepheid variable stars with a luminosity of about 10^3 L ☉ have a period of approximately _____ days.

3 or three

Astrophysicists have determined that most stars form with masses between a lower limit of ______ M☉ to an upper limit of about ______ M☉. (Select two answers.)

30 0.1

The Schwarzschild radius is directly proportional to mass and the Schwarzschild radius of the Sun is approximately 3 km. What is the approximate Schwarzschild radius for a 10 M☉ star?

30 km

About how many times more massive than Earth is the Sun?

300,000

On a typical H-R diagram, what would be good upper and lower limits for the temperature axis (in K)? (Select two.)

30000 3000

Match the minimum temperatures for fusion with the appropriate reaction. (Temperatures are approximate and for massive stars.)

5 million K-Hydrogen into helium 100 million K-Helium into carbon 600 million K-Carbon into neon and helium 2 billion K-Oxygen into silicon and helium billion K-Silicon into iron

The lifetime of a star is t = M/L x 10^10 years (with M and L in solar units). The Sun will last about 10 billion years. A star that has five times the Sun's mass is about 1000 times as luminous. How long will it last?

50 million years

You observe a star whose wavelength peaks at 580 nm. According to Wien's law, what is its temperature?

5000 K

The formula for the Schwarzschild radius is shown. Note that it is proportional to mass and that the Schwarzschild radius of the Sun is about 3 km. What is the approximate Schwarzschild radius for a 20 M☉ star?

60 km

Match the elements found in stars to what percentage of the star they comprise (percentages are given by mass).

71%-Hydrogen 27%-Helium 2%-Oxygen, carbon, and other elements

Although white dwarfs themselves can have masses up to about 1.4 M☉, because of stellar winds and the formation of a planetary nebula late in a star's life, white dwarfs can form from stars up to about ______ M☉.

8

The cut-off between low-mass and high-mass stars is usually taken to be around ______ solar masses.

8

Using the mass-luminosity relation, we can predict that a star with a mass of 2 M☉ would have a luminosity between ______.

8 and 16 L☉

In general, nucleosynthesis of heavy elements such as silicon or iron occurs in star with a mass greater than about ______.

8 solar masses

Stars with masses up to about ______ M☉ will become white dwarfs at the end of their evolution, but they will expel most of their outer layers so that the white dwarf has a mass of about ______ M☉.

8, 1

Select the events that occur during a hypernova.

A burst of gamma rays is emitted. A black hole is left behind. Material is ejected along jets.

Although they are difficult to detect, there are several neutrino detector experiments around the world. What might a sudden burst in the neutrino count indicate before it was obvious to telescopes?

A core-collapse supernova

Select all the things that happen in core-collapse supernova.

A dramatic increase in luminosity An enormous release of neutrinos A sudden expulsion of some outer layers of the star A sudden collapse of the outer layers of the star

What kind of telescope would be most likely to detect and identify a kilonova event (a neutron star merger)?

A gravity wave observatory

Examining the H-R diagrams of two clusters, you find cluster A has spectral type B stars on the main sequence and cluster B has no stars brighter than spectral type K on the main sequence. Which statement is true?

A is an open cluster. B is a globular cluster or an old open cluster.

Select all the choices that could cause a cloud to collapse and form stars.

A pressure wave from a nearby supernova The gravity of a passing star Colliding with another cloud

You would be most likely to observe mass transfer result in novas in a close binary of which stars?

A red giant and a white dwarf

Match the labels to their descriptions to describe the diagram of an X ray pulsar.

A-A hot spot B-X rays from the surface C-Magnetic field that channels matter D-Matter falling onto the pulsar E-Rotation axis

Match the descriptions to the labels in the formation of a hypernova blast.

A-A star greater than 20 M☉ runs out fuel and its core collapses. B-A black hole forms in the center of the star. C-The collapsing star spins faster and forms a disk and jets because of conservation of angular momentum. D-Jets form, beaming gamma rays in a burst. E-Black hole is left.

Match the terms to the labels in the figure demonstrating a nova.

A-Companion star B-Accretion disk C-Mass transfer D-White dwarf E-Nova F-Nova stella, "New star"

Match the letter to the name of the region of the Sun.

A-Core B-Radiative Zone C-Convection Zone D-Photosphere E-Chromosphere F-Corona

Match the term to the appropriate part of the diagram.

A-Interstellar cloud B-(Debris) disk C-Protostar D-Bipolar flow

Match the star or kinds of stars with the region on the H-R diagram where you would find them.

A-Main-sequence B stars B-Red giants C-White dwarfs D-Main-sequence M stars

Match the labels to the appropriate particle in the CNO diagram.

A-Nitrogen atom B-Carbon atom C-Helium nucleus A-Has atomic mass of 14 B-Has atomic mass of 12 C-Has atomic mass of 4

Identify the evolutionary stages of a high-mass star by matching the names to the labels in the diagram.

A-Protostar B-Main sequence C-Pulsating phase D-Supergiant E-Supernova F-Neutron star

Identify the evolutionary stages of a low-mass star by matching the names to the labels in the diagram.

A-Protostar B-Pre-main sequence star C-Main sequence D-Red giant E-Yellow giant F-Planetary nebula G-White dwarf

Match the names to the labels in the figure.

A-Roche lobe D-Accretion disk B-White dwarf C-Companion star E-Mass transfer point

Match the descriptions to the layers of a neutron star identified in the diagram.

A-Superfluid neutrons B-Crust (likely composed of iron) C-Atmosphere (primarily hydrogen)

Match the statements to the part of the diagram they describe.

A-These are sunspots A-Flares occur here B-These are prominences B-Gas can flow along these structures defined by the magnetic field.

Match the descriptions to the letters of the stages in the figure.

A-Two protons combine to form an isotope of hydrogen. B-Two gamma rays are formed. C-An isotope of helium is formed from two types of hydrogen D-One helium nucleus and two protons are formed

Match the letter to the stage of a low-mass star's evolution.

A. Planetary nebula D. White Dwarf C. Red Giant B. Main sequence

As a general rule, about how long does a star spend as a red giant, compared to how long it spends on the main sequence?

About 1/10 as long

As a general rule, how long does a low-mass star spend as planetary nebula, compared to how long it spends on the main sequence?

About 1/1000000 as long

Match the properties to the appropriate type of variable star.

All of them-Change apparent brightness Pulsating variable-Variation caused by expansion and contraction of radius Irregular variable-Variation caused by material falling on the star Pulsating variable-Have highly regular periods of hours to years Irregular variable-Usually very young or very old stars

Which statement best describes differential rotation on the Sun?

Areas near the north pole take 30 days to complete one rotation, but areas near the equator take only 25 days.

Select all that are correct about visual and spectroscopic binaries.

Astronomers can determine the orbit speed for both types. Astronomers can determine the orbit size for both types.

Match the layers of a neutron star with their thickness.

Atmosphere-A few millimeters Crust-A few hundred meters Liquid layer of neutrons-About 10 kilometers

Select all the choices that describe what might happen when a solar storm or coronal mass ejection reaches Earth.

Auroras Surges in electrical transmission cables Disruption of satellite communications

The image shows an ultraviolet image of the Sun, which highlights activity in the solar atmosphere, which is dominated by magnetic activity. Rank the regions by the size of the sunspots you would be likely to find, with the largest at the top.

B A C

The image shows a magnetogram of the Sun. The yellow and blue represent the strength of opposite polarities of the magnetic field. Rank the locations according to how large a sunspot you would be likely to find, with the largest at the top.

B C A

The _____ lines is the name for the set of hydrogen absorption lines that occur in the visible spectrum. These lines represent electron transitions from the n = 2 orbital.

Balmer

The hydrogen lines in the visible spectrum are known as ______ lines, after the scientist who discovered their pattern of wavelengths.

Balmer

Match cause to effect in the following statements describing the role of mass in a star's lifetime.

Because a star has a large mass,-the core is under tremendous pressure. Since the pressure in the core is high,-the temperature in the core is high. Largely as a result of a high temperature in the core,-the rate of fusion is high. Because the rate of fusion is high,-the lifetime of the star is relatively short.

Why does a low-mass star eject its outer layers to form a planetary nebula late in its life?

Between shell and core fusion, the core is producing much more energy than during earlier phases of the star's life.

Match these black hole scenarios to the best way to observe them or infer their existence.

Black hole merger-Detect gravitational waves with LIGO Black hole in a binary system-Use the modified Kepler's law and estimate the companion's mass based on its type Accreting black hole-Obtain the spectrum with an X-ray telescope

The vast majority of the stars plotted on an H-R diagram, _____% of them, create a line called the "main _____."

Blank 1: 90 or ninety Blank 2: sequence

Astronomers Ejnar _____ and Henry Norris _____ independently developed the H-R diagram, a valuable tool for understanding stars.

Blank 1: Hertzsprung Blank 2: Russell

In the stellar luminosity classification system, the brightest supergiants are class _____, and the majority of main-sequence stars are class _____. (Remember to use roman numerals.)

Blank 1: Ia Blank 2: V

For two carbon nuclei to fuse, they must overcome the _____ force holding the nuclei apart to allow the short-range _____ force to act.

Blank 1: electromagnetic, electrostatic, or Coulomb Blank 2: strong

The amount of _____ an object (such as a star) emits each second is called its _____.

Blank 1: energy or light Blank 2: luminosity

The continued existence of a star in any phase of its evolution depends on a balance between the inward force of _____ and the outward _____force from hot gas.

Blank 1: gravity Blank 2: pressure

The continued existence of a star in any phase of its evolution is a balance between the inward force _____ of and the outward _____ of hot gas.

Blank 1: gravity Blank 2: pressure

For a star to be stable, the force of gravity contracting the mass must be in balance with the radiation and gas pressure from the energy liberated by fusion that is trying to expand the star. This condition is known as _____ _____.

Blank 1: hydrostatic Blank 2: equilibrium

The graph shows a relationship between the relative numbers of stars with different masses that form when a cloud collapses. It is called a(n) _____ _____ function.

Blank 1: initial Blank 2: mass

Stars can only form in regions that have _____ temperatures, because otherwise the gas pressure would prevent the cloud from collapsing in the first place.

Blank 1: low, cool, cold, colder, or cooler

Einstein's famous equation of E = mc^2 shows that _____ can be converted into _____ as a method of powering the Sun.

Blank 1: mass or matter Blank 2: energy or radiation

In the _____ zone, energy is carried outward by photons that are continuously absorbed and re-emitted by plasma that hardly moves, whereas in the _____ zone, energy is also carried outward by motion of the gas.

Blank 1: radiative Blank 2: convection or convective

A kind of star (or other celestial object) whose luminosity can be accurately predicted by studying its spectra or other properties is called a _____ _____.

Blank 1: standard Blank 2: candle

The hot, glowing gas in this image is a _____ _____, and the tiny dot near the center is probably a star _____.

Blank 1: supernova Blank 2: remnant Blank 3: neutron

The pressure of an ideal gas depends on both the _____ and _____ of the gas.

Blank 1: temperature Blank 2: density

The Stefan-Boltzmann law describes how _____ and _____ are related to luminosity. (Use one word per blank.)

Blank 1: temperature Blank 2: radius, size, or area

The star Altair has a power output of about 4 × 1027 watts. This means that it produces as many joules of energy per second as _____ Suns and has a luminosity of _____ solar luminosities. (Enter the nearest whole number.)

Blank 1: ten or 10 Blank 2: ten or 10

A small, dense clump of gas that collapses to form a star is called a _____ globule.

Bok

A dim, red star might be a nearby low-mass star or a distant red giant. Which two properties would enable you to immediately calculate the luminosity of the star, and therefore determine which it is?

Brightness Distance

The intensity of light and the strength of gravity both vary as inverse-square laws. Match the parts of the inverse-square law for brightness with parts that act the same in the inverse-square law of gravity, FG = G m1xm2/d^2

Brightness-Force of gravity (decreases with distance) Luminosity-M1 × M2 (an intrinsic property of the object(s), stays constant with distance) 1/4π-Newton's constant G (constant) Distance (from observer to light source)-Distance between masses

At the end of a 5 M☉ star's main-sequence phase, where will it be on the H-R diagram?

C

Which of these stars appears the brightest from Earth?

Canopus, magnitude -0.74

Select all the choices that describe common white dwarf compositions.

Carbon-oxygen core surrounded by thin layer of helium and hydrogen Helium core surrounded by thin layer of hydrogen

Which astronomer explained why the temperature of a star affected the depth of the absorption lines in the spectrum?

Cecilia Payne-Gaposchkin

The distance ladder can be extended beyond distances where parallax measurements are possible by using _____ variable stars. Hubble made use of these to measure the distance to other galaxies.

Cepheid

Select all of the variable stars that can be used as standard candles.

Cepheids RR Lyrae

The theoretical upper limit on a white dwarf's mass of 1.4 M☉ is called the _____ limit.

Chandrasekhar

Select all the statements about the interaction of magnetic fields and particles that are true.

Charged particles can drag a strong magnetic field around. Charged particles spiral around a strong magnetic field. A strong magnetic field can drag charged particles around.

You examine the H-R diagrams of two clusters. Cluster A has no stars brighter than stellar spectral type F, and cluster B has none brighter than type G. Which statement is true?

Cluster B is older.

Match the terms related to white dwarf binary star systems to their definitions.

Companion-The other star in the binary system; may be a giant or a main sequence star Nova-A periodic eruption of hydrogen burning from the white dwarf surface Accretion-The process of mass transfer to the white dwarf Type la Supernova-Happens if the white dwarf accretes enough matter to exceed the Chandrasekhar limit Mass Transfer-The exchange of mass in a binary, from a main sequence or giant star to a compact star Roche Lobe-A teardrop shaped volume beyond which material will be lost to a companion star

Select properties of the Sun that are studied using spectra.

Composition Motions in the photosphere Surface temperature

In the _____ zone of the Sun, energy is transported to the surface through the motion of gas (as well as by photons).

Convection

Match the layer of the Sun to its approximate temperature.

Core-15,000,00(0) Photosphere-6000 Convection Zone-1,000,000 Radiative Zone-5,000,000

Match each solar phenomenon to its description.

Coronal mass ejections-Bubbles of violently ejected plasma as wide or wider than the Sun Flares-Violent X-ray and radio emissions associated with gas accelerated by the sudden changes in the magnetic field Prominences-Glowing arcs of gas confined in magnetic field lines Aurora-Visible light emission by particles from the solar wind or ejections interacting with Earth's atmosphere

Select all the correct descriptions of the picture, which combines visual light images (white stars and red hydrogen emission) with X-ray images (green to violet colors).

Cosmic rays are accelerated by magnetic fields in this object. This is a Type Ia supernova remnant. The hazy green areas (some labeled G) are emission from hot iron and silicon.

At the end of the Sun's main-sequence phase, where will it be on the H-R diagram?

D

Select all of the following that would definitely increase the pressure of an ideal gas.

Decreasing the volume without changing the temperature Increasing the temperature without changing the volume

Match the type of gas to the behaviors described.

Degenerate-Describes the gas in white dwarfs Ideal-Pressure is proportional to density multiplied by temperature. Ideal-Describes the gas in the Sun Degenerate-Pressure depends on the density only.

Which stellar property explains why lines of the same elements appear narrower in the spectra of very luminous giant stars (luminosity class I or III) than in main sequence stars (luminosity class V) of the same spectral type (e.g. "G")?

Density of the surface layers

Select all the ways that astronomers learn about the interior of the Sun.

Detecting neutrinos created by fusion reactions Comparing predictions from detailed modeling to the actual solar spectrum Measuring oscillations and vibrational patterns on the solar surface

Match the approximate location in the H-R diagram with the kinds of stars you find there.

Diagonal line from upper left to lower right-Stars in the normal part of their existence Upper right-Older giant stars Lower left-Hot dead stars Lower middle-Older low-mass stellar remnants Top middle down to center-Variable stars

Match the letter to the star's stage of evolution.

E-Protostar C-White dwarf B-Helium-burning A-Main lifetime

Match the cluster H-R diagrams to the stage of evolution of the stars.

E-The oldest cluster B-All stars at zero-age main sequence A-Stars are still forming. C-The hottest stars have just left the main sequence.

Match each object with the escape velocity from its surface.

Earth-11 km/sec The Sun-600 km/sec A typical neutron star-180,000 km/sec A black hole-300,000 km/sec

The graph shows a "light curve" for a binary star system. What is the best description of this binary?

Eclipsing binary

Which types of binaries need to be seen edge-on, or at least somewhat tilted, for us to detect them as the type listed? (Select all that apply.)

Eclipsing binary Spectroscopic binary

Which of these describe a degenerate gas? (Select all that apply.)

Electrons are packed tightly. It does not contract when it cools. The gas is very "stiff" (uncompressable).

Select all that describe the star shown in the figure.

Emits beams of radio waves or X rays Rapidly spinning Pulsar

Select all the net products of the CNO cycle. The CNO cycle occurs in massive stars.

Energy Helium

When astronomers were finally able to start identifying X-ray, visible, and radio afterglows that correlated with gamma-ray bursts, they discovered a correlation with what kind of object or event?

Especially energetic supernovae

Match the terms relating to black holes to their descriptions.

Event horizon-A sphere surrounding a black hole at the Schwarzschild radius Schwarzschild radius-The distance from a black hole at which the escape velocity is the speed of light Escape velocity-The speed required to escape an object's gravity Escape velocity-Another term for a black hole; a point of extreme curvature in space

Which kind of binary system would be the fastest for making the measurements needed to use Kepler's third law to determine the mass of the stars?

Face-on visual binary with a short period

True or false: According to Einstein's equation E=mc^2, mass can be burned to create energy, in the same way that we burn coal to create heat.

False

True or false: After the red giant phase, the Sun will become a black hole.

False

True or false: Generally, the larger the black hole, the higher its density.

False

True or false: More than 15% of the Sun's mass will be lost as the solar wind during the main (hydrogen-burning) part of its life.

False

True or false: Red giants are luminous because they are hot.

False

True or false: The CNO cycle in main-sequence stars converts hydrogen into carbon, nitrogen, and oxygen.

False

True or false: The absorption spectrum from a star will always show the spectral absorption lines of all the elements present in the surface layers.

False

True or false: The center of mass of a binary system can be at the exact center of the larger object, if it is massive enough (such as the Sun and a planet).

False

True or false: The energy radiated as light from and used to create pressure to support a white dwarf comes from fusing helium into carbon or carbon into oxygen.

False

Massive stars contract rapidly. Why does this help them to reach fusion conditions at lower core densities than low-mass stars?

Fusion requires high pressure, which depends on temperature and density. Rapid contraction results in high temperature.

Select all the statements that help explain why sunspots remain colder than their surroundings.

Gas flows into the cooler region, compressing magnetic field lines there. Strong magnetic fields limit the possible motions of the plasma, disrupting the normal convection.

The balance of which two forces is the most important in determining the overall structure and the final fate of stars?

Gas pressure Gravity

Match each solar feature to the layer in which it is observed.

Granulation-Photosphere Spicule-Chromosphere Hot Streamers-Corona

The Sun's energy output is about the same as that of 100 billion atomic bombs every second, an amount difficult to imagine. Yet, the Sun is stable and has been for billions of years. Which force is most responsible for keeping this output from destroying the Sun?

Gravity

What makes it essentially impossible to create a small black hole out of, say, a lump of rock, when a much bigger object such as a giant stellar core can spontaneously become one?

Gravity is the most efficient compressive force, and it is already failed on the rock.

The equations for both gravitational force and brightness have the same dependence on distance. Select the correct descriptions of their behavior.

Gravity or brightness drop by a larger factor than the distance increases. Both are inverse-square laws.

Select all that accurately describe a magnetar.

Has an extremely strong magnetic field A source of X-ray and gamma-ray radiation A kind of pulsar

Because they must have a temperature, black holes actually emit energy in the form of _____ radiation, named after the scientist who theorized it must exist.

Hawking

If the pressure of the Sun's hot gas holds it up against gravitational collapse, why must the Sun continually create energy from matter to remain stable?

Heat energy flows from hot objects to cold objects.

Which astronomers were instrumental in developing the type of plot of stars shown here?

Henry Norris Russell Ejnar Hertzsprung

Match each star's mass to the description of its convection zone.

High mass-Convection only occurs very near the core. Solar mass-Convection only occurs in the outer layers of the star. Very low mass-Convection occurs throughout the entire star.

Choose the sentence that best explains the journey of photons through a star.

High-energy photons created in the core are absorbed and re-emitted many times, eventually transformed into millions of lower-energy photons.

The diagram represents the conditions at the cores of young high-mass and low-mass stars. Fusion occurs in both cores. Match the physical conditions to the appropriate type of star.

High-mass-Faster velocity particles High-mass-Lower density Low-mass-Slower velocity particles Low-mass-Higher density

Select all that describe protostars.

Higher luminosity while accreting than after it is stable Often hidden in dust clouds Are easier to observe in infrared

Which is the best description of how recurrent novae occur in binaries in which mass is transferred from a companion star to a white dwarf?

Hydrogen builds up on a white dwarf until a layer undergoes thermonuclear runaway and all fuse at once.

Match the types of supernovae to whether or not they show hydrogen lines, indicating the presence of the upper layers of the star when it explodes.

Hydrogen lines-Type II (core-collapse) No hydrogen lines-Type Ia (white dwarf) No hydrogen lines-Type Ib (core-collapse) No hydrogen lines-Type Ic (core-collapse)

In addition to the right angle (V), which is known, select all the parts of the triangle that you can easily measure to use triangulation to find the distance to an object.

II III

Match the luminosity classes to the appropriate descriptions.

Ia-Bright supergiants Ib-Supergiants II-Bright giants III-Ordinary giants IV-Subgiants V-Main sequence

Select all the actions that would increase the pressure in an ideal gas (assume you only do one action at a time and everything else remains constant).

Increase the temperature. Move the atoms closer together.

It can be helpful to visualize the curvature of space as a flow that affects your (or a photon's) ability to move through it, like a current. In this visualization, how would you describe the flow at the event horizon of a black hole?

Inward at the speed of light

You analyze the spectrum of a Type Ia (exploding white dwarf) supernova. Which elements would you expect to find in large quantities?

Iron Silicon Carbon

Select all that are features of a supernova explosion.

It emits a shower of neutrinos. It only lasts a few minutes to a few hours.

How are newly created silicon, iron, and nickel atoms dispersed throughout the galaxy?

It happens when white dwarfs explode as supernovae.

The diagram shows the period-luminosity relation for variable stars. How does the luminosity of a Cepheid with a period of 20 days compare to one with a period of 5 days?

It is 10 times greater.

What is Hawking radiation?

It is a very low-temperature blackbody spectrum emitted by black holes.

The collapse of a cloud releases gravitational potential energy. Where does the energy go?

It is emitted from the cloud as line radiation. It is converted into heat in the cloud. It becomes kinetic energy of moving parts of the cloud.

Select all that accurately describe the changes in a massive star after it leaves the main sequence. The figure may be helpful.

It is surface temperature drops. It maintains about the same luminosity until it explodes.

Select all the correct statements about the solar atmosphere.

It lies above the photosphere. It consists of the chromosphere and corona.

Select all that correctly describe the Hipparcos satellite.

It measured parallaxes without the blurring effects of the atmosphere. It measured distances to stars as far away as 500 parsecs.

What slows down the first step in the proton-proton chain?

It requires a weak force interaction to convert a proton into a neutron.

Select all the correct descriptions of solar seismology (helioseismology).

It uses waves in the interior of the Sun. It shows that the Sun has used up half of the hydrogen in the core. It can measure density inside the Sun

For many years, scientists were puzzled that the Sun seemed to produce only about a third as many neutrinos as predicted. How was this puzzle resolved?

It was discovered that the solar neutrinos changed type on the way to Earth and new neutrino telescopes detected the other types.

If the Sun did not constantly produce energy, what would happen? (Select all that apply.)

Its core temperature would decrease. The Sun would become unstable.

What important property of a neutron star might you be able to estimate if with a good measurement of its thermal (blackbody) luminosity and temperature?

Its size

Which astronomer discovered absorption lines in stellar spectra?

Joseph Fraunhofer

Which stars are mostly likely to undergo a helium flash during the red giant phase?

Low-mass stars

Select all that are axes in the H-R diagram.

Luminosity Temperature Spectral type

Match each property to the approximate range covered on its axis in the H-R diagram.

Luminosity-Factor of 1010 Temperature-Factor of 10 Mass-Factor of 100

Match the terms to their descriptions.

Luminosity-The energy emitted per second as light, measured in watts Apparent brightness-How bright an object looks Inverse-square law-A mathematical relationship between how bright an object looks, how much energy it emits, and its distance squared

Match the terms to their descriptions and units.

Luminosity-Watt = Jsec Brightness-Wm2 = Jsec m2 Luminosity-Total energy per time emitted Brightness-Power received per square area

Based on the location of the peak of the emission, the spectral type for a star with the spectrum shown in the image is most likely ______.

M, or B depending on picture M-peak in the red B-peak in the purple

Match the spectral types to the temperature ranges and line features.

M-2000 to 3500 K; Titanium Oxide lines A-7500 to 10,000 K; strongest hydrogen lines B-10,000 to 30,000 K; helium lines L-1300 to 2000 K; Metal hydride and water lines T-700 to 1300 K; water and methane lines Y-under 700 K; possibly ammonia line

Select all the statements that explain how the Sun's magnetic field makes the corona hot.

Magnetic waves make particles move faster. The corona is less dense than the surface.

Match each term related to stellar evolution with an appropriate definition.

Main sequence-Describes the "regular" phase of a star's existence Protostar-An accreting star surrounded by infalling cloud material Bipolar outflow-Opposing jets of material ejected from the star Neutron star-A compact stellar remnant of a massive star Planetary nebula-The ejected outer layers of a low-mass star Supernova-An implosion-explosion of a high-mass star

Compare a red giant to a main-sequence star of the same mass.

Main-sequence-higher density near the surface Red giant-higher luminosity Red giant-hydrogen burns in a shell around the core Red giant-larger volume Main-sequence-hotter surface

Match each experiment to a selection effect you would need to take into account.

Make an H-R diagram using all stars above a certain brightness-There will be more highly luminous stars in the sample than less luminous ones. Find the brightest object in the sky-The results depend on what kind of telescope you use. Compare mass and orbital distance of exoplanets found using radial velocities-The sample favors high-mass objects at small distances. Count the number of low-mass stars using optical images-The results may miss objects whose temperatures peak in the infrared.

Match the properties of stars to the approximate numerical ranges of values observed to exist.

Mass (in M☉)-About 0.1 to 100 Luminosity (in L☉)-About 0.0001 to 10^5 Radius (in R☉)-About 0.01 to 1000 Temperature (in K)-About 3000 to 30,000

Which are good methods of observing black holes? (Choose all that apply.)

Measuring gravitational effects Studying X rays from an accretion disk

Which statement best describes the elements produced in the cores of massive stars after they leave the main sequence?

Mostly even numbered elements from helium to iron

Select all that describe neutron stars.

Much smaller than a white dwarf Similar to a giant atomic nucleus Predicted before observed

Why are neutron star binaries rarer than white dwarf binaries?

Neutron stars have higher velocities through space than white dwarfs. Supernovas eject so much mass the binary might not have enough gravitational force to stay together afterward. More massive stars produce neutron stars, and massive stars are less common.

Match the systems to whether or not you might expect visible-light novas to occur, if the orbits are close enough.

Nova-white dwarf and red giant Nova-white dwarf and an orange main sequence star Would not produce a nova-brown dwarf and red giant Would not produce a nova-black hole and blue supergiant

Select all of the stars that are irregular variables.

Novae T Tauri stars

Match equal values of angular measurement.

One Degree-60 arc minutes One Degree-3600 arc seconds One Degree-1 degree One Arc Minute-60 arc seconds One Arc Minute-1/60 degree

The 400 years of astronomical history since telescopes, compared to the age of a typical star, is about the same as which comparison below?

One minute in the forest vs. the typical lifetime of a common tree

A selection effect occurs when the tools or method used in an experiment produce a trend in the results that is not related to the actual properties of what you are studying. Imagine you are taking a census of how many people are each age in your town. Which of the following methods would produce the largest selection effect in your data?

Only counting people in an elementary school on a weekday

Match the characteristic to the appropriate cluster.

Open cluster-An example is the Pleiades. Globular cluster-Some tens of pc across (100 to 200 ly) Open cluster-A few pc across (up to 40 ly) Open cluster-A hundred to a thousand stars Globular cluster-Few young stars, many red giants Globular cluster-Gravitationally bound

Select all that describe an eclipsing binary.

Orbits are edge-on as seen from Earth. Stellar spectra show Doppler shifts.

Select all the correct descriptions of binary stars.

Over 40% of stars have companions. Binary stars orbit each other around their common center of mass. Astronomers use binary stars to calculate the masses of stars.

Match the terms to their definitions.

Photometry-The measurement of brightness of a light source Standard candle-An object of known luminosity Method of standard candles-The measurement of distance by using objects of known luminosity Apparent magnitude-A value representing the observed brightness of a star Absolute magnitude-A value representing the luminosity of a star

Why does it take hundreds of thousands to millions of years on average for energy to travel from the Sun's core to its surface?

Photons in the radiative zone travel very short distances before being absorbed and re-emitted in random directions.

A gas that is so hot that the atoms have been stripped of their electrons (making them ions) is called a

Plasma

If opposite electrical charges attract each other, why do the positively charged nuclei and the negatively charged electrons in a plasma not simply recombine into atoms?

Plasmas are too hot.

_____ is created by the collisions of particles in a gas. It is higher when the gas is hotter or denser.

Pressure

Select all the processes that astronomers include in stellar models.

Pressure of hot gas Nuclear fusion Gravity Models of photon absorption and emission

Which stage of stellar formation is most closely associated with bipolar jets?

Protostar

Categorize the characteristics as typical of a pulsar or a white dwarf.

Pulsar-Spins many times per second Pulsar-Emits beams of radiation White Dwarf-Roughly the size of Earth White Dwarf-Must be less than 1.4 M☉ Both-Sometimes found in binary star systems

_____ variable stars change in luminosity as a result of a regular pattern of expanding and contracting in size.

Pulsating

Select all of the phases that a high-mass star can pass through during its life.

Pulsating (variable) yellow giant Neutron star Red giant Main-sequence

What is the source of pressure that holds up a white dwarf?

Quantum mechanical limits on how many electrons can be packed into a volume

Which of these stages will the Sun's evolution include? (Select all that apply.)

Red giant Planetary nebula White dwarf

Match the variable star to its type.

Regular-RR Lyrae Regular-Cepheid Regular-Mira variable Irregular-T Tauri star Irregular-Nova (white dwarf)

In the figure, the green vectors indicate the forces acting at different distances from a large and small black hole. They are drawn to scale. Match the descriptions of the overall force and the tidal force to each type of black hole.

Small black hole-Larger tidal force Small black hole-Smaller gravitational force Large black hole-Larger gravitational force Large black hole-Smaller tidal force

If stellar cores do not create elements heavier than iron, where do heavier elements come from?

Some are produced in the blast waves of supernovae.

Why are elements such as selenium or platinum scarce in the universe, but carbon, iron, and oxygen are common?

Some elements are created in the cores of stars, but others are only created in supernova explosions and rare neutron star-neutron star mergers.

What is necessary for a molecular cloud to collapse?

Something must trigger a disturbance.

Match the methods of direct stellar radius measurements with their descriptions.

Space telescopes-Avoids blurring by the atmosphere Speckle interferometry-Uses a large telescope with a high-speed camera Interferometry-Combines observations from multiple small telescopes

Spectra of three stars are shown. Which one will look the most blue? (Hint: the ratios of different colors are important; recall that white light contains similar contributions of all colors.)

Spectrum (A) (blue line)

Which spectrum is from the object with the highest temperature?

Spectrum (A) (blue line)

Model spectra for two stars are shown. Which has the higher temperature, or are they the same?

Spectrum A

Which of these spectra is from the object that would look the reddest?

Spectrum C

You measure the brightness of two stars from Earth (X and Y). Which one of the following could be true of X and Y if star X is brighter than star Y?

Star X is twice as luminous as star Y and is at one-quarter the distance.

Match the spectral types and line features to whether an object would most likely be a star or brown dwarf.

Star-M; Titanium Oxide lines Star-A; strongest hydrogen lines Star-G; strong calcium lines Brown Dwarf-L; metal hydride lines Brown Dwarf-T; water and methane lines Brown Dwarf-Y; coldest objects

Match each characteristic based on whether it more closely describes an open cluster or stellar association.

Stellar association-Identified by groups of young, very close stars Stellar association-Generally more spread out, up to hundreds of light-years Open cluster-More compact, under 20 light-years Open cluster-Have more stars, up to a thousand Stellar association-Typically, all the stars formed from the same cloud.

Which are good methods of observing black holes? (Choose all that apply.)

Studying X rays from an accretion disk Measuring gravitational effects

Select all the statements about sunspots that are true.

Sunspots usually occur in pairs. Sunspots are regions where magnetic field lines cut through the surface. Galileo observed sunspots with his telescope. Sunspots are cooler than the surrounding surface.

What type of light would be emitted by the spiraling charges in the figure?

Synchrotron radiation

In the 1990s, additional stellar types were created for brown dwarfs, objects cooler than M stars. Select all the spectral types that might be typical for brown dwarfs.

T L Y

Match the terms related to young stars to their definitions.

T Tauri-A kind of young star showing variability Protostar-A young star that shines mostly in the infrared Deuterium-A hydrogen atom containing a neutron and a proton in the nucleus Bipolar flow-Jets of material ejected perpendicular to the debris disk around a young star

Match the events or characteristics to the type of star most associated with them.

T Tauri-Irregularly variable luminosity T Tauri-Have bipolar outflows T Tauri-pre-main sequence Pulsating variable star-post main sequence Pulsating variable star-Periodically variable luminosity

Match the time segments indicated on the light curve with the measurements that can be made of the sizes and positions of the stars in a binary.

T1-Diameter of the smaller star T3+T4-Diameter of the larger star T2-Hot star in front of cool one T4-Cool star in front of hot one

Match the labels and terms to set up the H-R diagram.

Temperature-Is plotted on the X axis (X) Luminosity-Is plotted on the Y axis (Y) Temperature-Increases toward the lower left (LL) Luminosity-Increases away from the lower left (LL)

Select all that correctly describe luminosity.

The Sun has a luminosity of about 4 × 1026 watts. Luminosity is measured in units of watts. A star's luminosity is one factor in how long it lives.

Select all the correct statements concerning the link between the solar cycle and Earth.

The Sun's Maunder minimum coincided with a "little ice age" in Europe. The solar wind may drive changes in weather patterns.

Select the reasons why it is difficult to obtain direct images of stars (other than the Sun).

The atmosphere limits the capabilities of the largest telescopes, which are on Earth. Interferometry, which can resolve individual stars, only works well for some of the larger and brighter stars. The angular size of most stars is smaller than the diffraction limit of even large single telescopes.

Once the core becomes iron, why do massive stars collapse instead of simply fusing the iron into heavier elements?

The bonds between nuclear particles in heavier elements require more energy than they do in iron.

If the corona is thousands of times hotter than the photosphere and the chromosphere is tens of times hotter, why do we see the photosphere as the "surface" of the Sun?

The chromosphere and corona are much less dense than the photosphere.

Particularly after observations in the late 2010's, what kind of event is believed to produce significant amounts of high atomic number elements, such as gold, uranium or platinum?

The collision of two neutron stars

What happens after a helium flash? (Choose all that apply.)

The core stabilizes. The outer layers heat up. The outer layers shrink.

Select all the spectral properties that vary with temperature.

The depth, or darkness, of spectral lines Which lines are visible

What is converted into energy in the proton-proton chain?

The difference in the mass of four protons and a helium nucleus

Which information from the light curve is more important for determining the sizes of the stars in an eclipsing binary?

The durations of the eclipses

Why do the durations decrease as a star progresses through the reactions in the table?

The energy released by a single reaction decreases as the atoms increase in mass.

Just as like charges repel, like magnetic fields repel (north pushes away north). How does a sunspot, a region of strongly concentrated magnetic field, persist? The magnetic field is tied to the charged particles in the gas.

The forces involved in the gas flow are stronger than the effect of the magnetic field on the gas flow. Gas pressure confines the spot.

If the Sun is a hot gas all the way through, why is the visible spectrum continuous with absorptions lines, instead of emission lines?

The gas is high enough density that the Sun acts like a hot, dense object and emits blackbody radiation.

Select all that accurately describe Type Ia (white dwarf) supernova remnants.

The gas shell expands at thousands of kilometers per second. No compact remnant of the core is left behind. Magnetic fields in the shock wave accelerate electrons and protons.

Why is the density inside the Sun greater than at the surface?

The inner layers are compressed by the weight of the material above them.

How is the solar cycle is a result of differential rotation?

The magnetic field becomes twisted as it is dragged along by differentially rotating gas. Energy is released as it reverses and reorganizes.

You observe two stars with the same temperature, but one of them has a higher luminosity than the other. How is this possible?

The more luminous star is larger. Both emit the same number of photons per area, but the larger star has a bigger surface area.

Fourteen helium nuclei have as many protons plus neutrons (p+n) as one iron nucleus. Likewise, 197 iron nuclei have as many as 56 gold nuclei. Why do not you get energy out of fusing iron into gold, if you do from fusing helium into iron? (The figure may help you.)

The pile of 56 gold nuclei has more mass than that of the 197 iron nuclei, whereas the pile of iron has less than the He.

Why does not the conversion of the protons and electrons into neutrons in the iron core of a massive star help to support the core against collapse, instead of causing one?

The reaction requires energy, rather than releases it.

You observe the spectra of stars in an eclipsing binary. Which star will show larger Doppler shifts in its spectrum?

The star farther from the center of mass will.

Which statements describe a neutron star-neutron star merger (collision)?

The stars spiral into each other because their orbits lose energy in the form of gravity waves. Large amounts of high atomic number elements, such as gold, are produced. A burst of gamma rays is emitted.

Neutron stars are sometimes observed in binary systems (typically in "X-ray binaries"). Why might this be surprising? (Select all that apply.)

The supernova explosion can give the neutron star enough velocity to escape the binary. The supernova that creates the neutron star expels most of the mass of the exploding star, and the companion may escape.

Select all the correct statements about the inside of the Sun.

The temperature increases toward the center of the Sun. Density increases toward the center of the Sun.

Select all the statements that describe white dwarfs' peculiar structure.

Their density is about 10^6 kg/L. If a white dwarf were to increase in mass, it would get smaller. Adjacent atomic nuclei are closer than the electrons' orbits.

What do the different types of pulsating variable stars (RR Lyrae, Mira, Cepheids) have in common?

They are old.

Which statement best describes astronomer's ability to observe the evolutionary changes of stars over time?

They cannot see individual stars change stages, but can draw conclusions based on the numbers and types of stars.

All of the white dwarf (Type Ia) supernovae show very similar light curves and total energies. Core-collapse supernovae can have very different light curves and energies, and even may (Type II) or may not (Type Ib, Ic) show hydrogen lines. Why are the core-collapse supernovae so different? (Select all that apply.)

They happen from stars with and without their outer envelopes. They happen from stars with a huge range of masses.

Why are scientists confident that the inside of the Sun is very hot?

They have confidence in the accuracy of their models of the Sun. Without high temperatures, the Sun would collapse.

Select the choices that accurately describe the neutrinos in a core-collapse supernova.

They transfer energy to the exploding layers, accelerating them. They carry significant energy out of the core. They may be detected before other changes are obvious.

Select all that are features of T Tauri stars.

They vary in brightness. They exhibit flows from their surface. They have giant starspots and flares.

Select all that are properties of neutrinos.

They weakly interact with matter. They can change among three types. They travel at nearly the speed of light.

To create a black hole, it is necessary to compress matter such that the mass M is contained within a sphere with a radius of the Schwarzschild radius, RS. Why is it difficult to create a black hole with a small mass (say, less than a solar mass)?

To pack matter that tightly would require overcoming neutron degeneracy pressure.

Match the measurements and methods used to find each velocity for a star.

Transverse velocity-Proper motion of the star Radial velocity-Wavelength shift of spectral line Space velocity-Can only be found from the other two velocities Transverse velocity-The distance to the star Radial velocity-Doppler formula Space velocity-Vector addition

Match the terms to the correct descriptions.

Transverse velocity-The speed of a star moving "sideways" to us, that is, across our field of view Radial velocity-The speed of a star moving toward or away from us, that is, along our line of sight Space velocity-The overall speed of a star and the direction is it moving compared to us

True or false: A supernova can shine nearly as bright as a galaxy.

True

True or false: All pulsars are neutron stars, but not all neutron stars are pulsars.

True

True or false: Early theories about the source of the Sun's power predicted lifetimes for the Sun that are too short.

True

True or false: The smaller the mass of a star, the longer it takes to get to the main sequence.

True

Match the technique to the information it provides about the Sun.

Use radar bounced off the Sun-Distance to the Sun Measure the Sun's angular size-Radius of the Sun Use Newton's version of Kepler's third law-Mass of the Sun Use Wein's law-Temperature of the Sun's surface Measure solar energy reaching Earth-Total power output of the Sun

You observe a binary system that has a red giant and some kind of dark companion. What would be the best way to determine if the object is a black hole or an old white dwarf?

Use the red giant's orbit and Newton's laws to find the mass of the companion.

Select the methods used to make direct measurements of the radii of stars.

Using interferometry through simultaneous observations with two or more smaller telescopes Observing with a space telescope above Earth's atmosphere Using speckle interferometry with a high-speed camera

Match the descriptions with the correct type of binary star.

Visual binary-Two separate stars are seen. Visual binary-Stars' orbits can be seen. Spectroscopic binary-Light of two stars seen as single blob Spectroscopic binary-Detected by Doppler shift of emission/absorption lines

Match the descriptions to the appropriate symbols in the equation for transverse velocity.

Vt-Transverse velocity, how fast in km/sec a star is moving "sideways" across our field of view 4.74 km/sec-Scaling factor d-The distance to the star μ-The star's proper motion pc-Indicates the measurement is in parsecs aracsec/yr-Indicates the measurement is in arc seconds per year

What was the solution to the solar neutrino problem?

We revised our theory of neutrino types.

One of the (net) nuclear reactions that occurs in the core of a massive star after it moves off the main sequence is 28Si + 28Si → 56Fe. If silicon has 14 protons, and iron has 26, how is this possible?

Weak-force interactions allow two protons to be converted into neutrons.

Why does a star that has become a pulsar have a much stronger magnetic field than when it was a main-sequence star?

When the star collapses to become a pulsar, the field is highly compressed.

Which of these will be the last stage in the Sun's life?

White dwarf

Match the terms to their definitions.

X ray burster-A neutron star that accretes hydrogen from a companion, then explosively fuses it X ray pulsar-A rapidly spinning neutron star that emits X rays from its surface Hot Spot-Region where material channeled along the magnetic field falls onto and heats the crust Accretion Disk-A region where material orbits a pulsar before falling onto it

What wavelength would be a good choice to study the thermal (blackbody) emission from an isolated neutron star?

X rays

Stars at points X and Y in this H-R diagram are forming in the same cloud. Match the comparative statements to the appropriate star.

Y-Less massive Y-Lower luminosity Y-Reaches the main sequence second X-More massive X-Higher luminosity X-Reaches the main sequence first

Match each term related to stellar evolution with an appropriate definition.

Yellow giant-A stable, helium-fusing phase of a star Variable star-An evolved star that regularly expands and contracts, changing temperature and luminosity Stellar wind-Outflow from a stellar surface Red supergiant-A late phase in a massive star's life during which elements such as oxygen and silicon are created in the core Black hole-The end state of the most massive stellar cores White dwarf-The end state of low-mass stellar cores

Select the statements that are correct.

You can see stars with visual magnitudes from 0 to 6 in a dark sky, plus a few even brighter ones. The magnitude system was created by an ancient Greek astronomer to rank how stars appeared to the naked eye.

A solar astronomer studying a spectrum of a sunspot observes that a spectral absorption line is split into two lines in a region of high magnetic field. This is known as the ______ effect.

Zeeman

In a region of high magnetic field such as a sunspot, a spectral line can be split into two or more lines. This is known as the _____ effect.

Zeeman

You measure the spectrum of a supernova in another galaxy and discover that it has no hydrogen lines. The supernova is ______ supernova.

a Type Ia (white dwarf)

A white dwarf accumulates enough mass from a companion star to exceed the Chandrasekhar limit. The result is ______.

a Type Ia supernova

The image shows an analogy of ______. (Select all that apply.)

a black hole curved space

In the triple alpha process of fusion, the result is ______.

a carbon nucleus

You would measure the typical proper motion of star over a year to be closest to ______.

a fraction of an arc second

The image shows a kind of aggregation of stars called _______.

a globular cluster

We could make a rough estimate of how the density of a black hole depends on mass as follows: Density = M/V ∝ M/Rs^3. Since the Schwarzchild radius is directly proportional to mass, we can replace RS with M in the proportionality. This means that a larger, more massive black hole has ______ as a smaller one.

a lower effective density

A type of star whose luminosity changes in a regular pattern as shown is ______.

a pulsating variable

Many planetary nebulae show an hourglass shape, as in the figure. This geometry could result from ______. (Select all that apply.)

a ring of dust and gas orbiting along the equator effects from the star's magnetic fields wind interaction with an orbiting companion

A supernova remnant can be described as ______.

a shock wave expanding at thousands of km/sec

A Bok globule is ______.

a small, dense clump that becomes a star

At a distance of many Schwarzschild radii from a black hole, you could describe space as being ______.

about the same as around any star of the same mass

Compared to Earth, a white dwarf is ______.

about the same size

Evidence that Type Ia supernovae are the detonation of an accreting white dwarf pushed over the Chandrasekhar limit includes ______. (Select all that apply.)

agreement between predictions of detailed models and actual supernova light curves observations of the runaway companion stars near Type Ia supernova remnants the similarity of their luminosities

The increase in sea surface temperatures on Earth since 1990 is ______.

almost certainly due to an increase in human-made greenhouse gases

It is possible to determine the distribution of masses of stars in a cluster because the stars ______. (Select all that apply.)

are all approximately the same age are all the same distance from us

Compared to open clusters, globular clusters ______. (Select all that apply.)

are larger in total mass have more stars are typically farther away

X ray pulsars ______. (Select all that apply.)

are typically less regular than radio pulsars emit thermal radiation from material accreted to their surface

Compared to a globular cluster, the stars in an open cluster ______. (Select all that apply.)

are younger are fewer are more spread apart

Pressure is directly created by ______.

atoms or molecules hitting surfaces they are in contact with (including each other)

Based on the diagram, you can conclude that an electron moving through a magnetic field line will ______.

be accelerated

Compared to the density of a 100 M☉ black hole, a 3 M☉ one would ______.

be more dense

If you are limited to making simultaneous observations from different sides of the Earth, a challenge in using triangulation to determine distances to Solar System objects (say, the Moon) is that ______.

because the distances are quite great, the tangent of the angle is very small, and therefore, the angles are very small

If you increase the energy of the electrons in a degenerate gas that is under pressure, the gas ______.

becomes hotter

When a low-mass star starts burning helium in its core, it ______.

becomes stable again for a time

A star is a "zero-age main sequence" star when it ______.

begins stably fusing hydrogen

Select (two) answers to complete the two sentences: Our brains estimate the distance to objects by using the method of ______. The baseline is the distance ______.

between our eyes parallax

Paired stars in gravitational orbit around each other are called _____ stars.

binary

Pulsating stars with a regular period ______.

can be used as standard candles

A spectrum of a glowing object such as a star ______. (Select all that apply.)

can be used to determine the elements present in the object shows effects dependent on the surface temperature of the object is a measurement of the amount of light, emitted as a function of wavelength

In main sequence stars, the mass-luminosity relation ______. (Select all that apply.)

can be used to show that Achernar, about 1000 times more luminous than the Sun, is a bit less than 10 times more massive tells us that all 1 M☉ stars have about the same luminosity

During a star's Mira variable stage, radiation pressure drives flakes of ______ out of the star.

carbon and silicon

The stellar winds from a Mira variable carry away ______. (Select all that apply.)

carbon flakes a significant fraction of the star's mass hydrogen, nitrogen and oxygen gas dusty grains

The larger the value you measure for the parallax of a star, the ______ the star is.

closer

The two stars shown must both ______.

complete their orbits in the same time

A pulsar spins very rapidly because of ______.

conservation of angular momentum when it formed

The graph shows occasional jumps in the rotation speed of a pulsar. These are called ______ and result from ______. (Select appropriate choices to complete the sentence.)

conservation of angular momentum when the star's structure (radius) changes glitches

An astronomer who records a visible light spectrum of a star will normally find it is a(n) ______.

continuous spectrum with absorption lines

According to the exclusion principle, two electrons cannot occupy the same space at the same time with the same energy. Therefore, if you increase the energy of the electrons in a degenerate gas that is under pressure, the gas ______.

contracts

As a red giant, a star has a ______ temperature and a ______ average density compared to when it was on the main sequence. (Select two.)

cooler smaller

Drawing on the information in this graph of the initial mass function, we can conclude that most stars are ______. (Select all that apply.)

cooler than the Sun low mass

Regions in the corona through which the solar wind escapes are called ______.

coronal holes

Astronomers developed an understanding of the initial mass function, the numbers of stars of different mass that form when clouds collapse, by ______. (Select all that apply.)

creating predictions with simulations of star formation including detailed physics measuring the distributions of stars in open clusters

You are triangulating the distance to the tree shown in the diagram. Note the triangle is a right triangle, although it is seen from an angle in the diagram. Which formula will give you the distance to the tree?

d = b tan α

The conservation of angular momentum requires that if a star's radius shrinks by a factor of 100, the velocity of the star's equator must increase by a factor of 100. If the period is the circumference divided by the velocity (2πR/V), then the period must ________.

decrease by a factor of 100^2

Over most of the range of the initial mass function shown in the graph, for an increase in the mass of stars by a factor of ten, the number of stars expected for that mass ______.

decreases by more than a factor of 10

A gas that is so dense that the electrons cannot be packed any tighter without violating laws of quantum mechanics is called a _____ gas.

degenerate

What property of the gas in the Sun's photosphere most explains why we can't see through it (that is, why it absorbs and re-emits light from below)?

density

Protostars differ from main-sequence stars because they ______. (Select all that apply.)

derive energy from contraction are surrounded by infalling material do not fuse hydrogen into helium

To use the method of standard candles, it is first necessary that astronomers ______. (Select all that apply.)

determine the actual luminosity of a single standard candle of the same type determine that the object is a standard candle and what kind, using spectroscopy or other means independently determine the distance to a known standard candle of the same type

The solar cycle is strongly related to the Sun's rotation.

differential

The Cepheid variable period-luminosity relation allows astronomers to determine the star's ______.

distance

The difference between a star's apparent magnitude (m) and its absolute magnitude (M) can be used to calculate its ______. (Hint: consider what each measures.)

distance

Through a telescope, two stars appear close to each other on the sky. However, according to a distance catalog, one is only ten light-years away and the other is 400 light-years away. What you see is called a(n) _____ star.

double or apparent double

If the temperature of a gas increases by a factor of 10, to keep the same pressure the density must ______.

drop to one-tenth its value

You observe two yellow G-type stars in a nearby star cluster at a known distance. One is 64 times brighter than the other. From this information, you can conclude that the brighter star has a radius _____ times larger than the dimmer one.

eight or 8

Red stars have the lowest surface temperatures, only a few thousand Kelvin. That means most stars are colder at the surface as red giants than they were when on the main sequence. This is mostly because ____.

even though they are producing more energy from fusion, their surface areas are much larger

Current thinking is that planetary nebula are affected by the star's rotation, and thus form in the shape of ______ related to the star's rotation axis.

expanding cones

Compared to a red star, a blue star will burn its fuel ______.

faster

Compared to the proton-proton chain, the rate of energy production via the CNO cycle is ______.

faster

In stellar modeling, astronomers must compute the ______ at each level in a star. (Select all that apply.)

force of gravity amount of convection hydrostatic equilibrium rate of nuclear energy production transmission of energy

The proton-proton (p-p) chain provides energy in stars similar to the Sun. The net reaction in the p-p chain is ______.

four protons are converted into a helium nucleus, energy, and neutrinos(ν)

When a large molecular cloud collapses, it ______.

fragments and forms stars

As a particular star ages, the composition of material on its surface changes, changing the spectrum. This star is probably ______.

fully convective

The Sun is powered by the process of nuclear _____ in its core.

fusion

As a star moves from the main sequence toward the red giant stage, it ______. (Select all that apply.)

gets larger fuses hydrogen in a shell around the core

Periodic jumps in the pulsation rate of a pulsar that result from changes in the star's radius are known as _____.

glitches

You observe a cluster that looks like a tightly packed ball of stars. This is most likely a(n) _____ cluster.

globular

In the layers above the photosphere, the density of the solar atmosphere ______.

gradually decreases

All over the Sun's surface, dark features surround large, rising pockets of gas. This texture of the solar surface is called .

granulation

The patchwork of regions of rising and falling gas at the top of the convection zone (in the photosphere) create ______.

granulation

As mass is added to a white dwarf, its radius decreases and the energy of the electrons increase. As the mass approaches the Chandrasekhar limit, ______.

gravitational force between the particles increases faster than the electron pressure and the star collapses

Below a certain mass, stars cannot form because ______. (Select all that apply.)

gravity cannot compress the gas enough the core never gets hot enough

A 500 M☉ cloud is unable to form a similarly huge star because ______.

gravity cannot overcome the radiation pressure in such a star

A white dwarf's mass cannot exceed the Chandrasekhar limit because then ______.

gravity would overcome electron degeneracy

"Zero-age main sequence" means that a star ______.

has just entered the main sequence

A star at point A on the yellow track in this HR diagram ______.

has just started fusing hydrogen into helium

Differences between low-mass and high-mass stars include the fact that high-mass stars ______. (Select all that apply.)

have higher core temperatures produce energy mostly by the CNO cycle

Nucleosynthesis is the process by which ______. (Select all that apply.)

heavy elements are formed in massive stars heavy elements are formed by fusion of lighter elements

Helium burning requires a higher temperature than hydrogen burning because ______.

helium has more protons the electric repulsion between helium atoms is stronger

For atomic nuclei to approach each other closely enough to fuse, ______.

high temperatures are needed

It is rare for very high-mass stars to form at all because ______. (Select all that apply.)

high temperatures reached during collapse prevent more mass from accumulating their high luminosity can disrupt the structure of the star

If a star moves from the main sequence to the red giant stage and its luminosity remains roughly constant, it is probably a ______.

high-mass star

Match the characteristics of a star moving off the main sequence to its mass.

high-mass-core develops multiple fusion shells high-mass-shorter main-sequence lifetime low-mass-undergoes helium flash low-mass-has a degenerate core

The inside of the Sun is ______.

hotter than the surface of the Sun (photosphere)

From observations of a visual binary with a known distance, you obtain the semimajor axis, in AU, and the period, in years. If you plug those values into M = a^3/p^2, the mass you will find will be ______. (Select all that apply.)

in solar masses (M☉) the sum of both stars' masses

In accordance with the conservation of momentum, if a star shrinks (without losing any mass), you expect its rotation speed to ______.

increase

As a molecular cloud collapses, its released gravitational energy ______.

increases the kinetic energy of atoms at its center

Over time, the fraction of carbon and oxygen in the composition of interstellar clouds ______.

increases, because stars create more and release it back

In theories of star formation, a mathematical relationship that tells how many stars form as a function of mass is called a(n) ______.

initial mass function

Stars form in ______.

interstellar gas clouds

Hydrogen makes up about 71% of the Sun, a G-type star, by mass. The fraction of hydrogen in other typical stars ______.

is about the same

When a star is in hydrostatic equilibrium, at each layer of the star the inward pull of gravity ______.

is balanced by outward pressure

When a star is in hydrostatic equilibrium, at each layer of the star, the inward pull of gravity ________.

is balanced by outward pressure

The figure shows that to see a star, a telescope must be tilted slightly (bottom row) compared to the actual line to the star, because of the Earth's motion through space. This proof of the Earth's motion ______. (Select all that apply.)

is called aberration of starlight is the same for all stars in the same region of the sky was measured before stellar parallaxes

The kind of diagram shown ______. (Select all that apply.)

is called an H-R diagram shows properties, not positions, of stars

An alternative visualization for the curvature of space is to imagine that space is flowing, affecting the motion of matter or light traveling through it. In this approach, one would imagine that as you approach a black hole, space ______.

is flowing into the black hole, increasing in speed until it is flowing at the speed of light at the Schwarzchild radius

is flowing into the black hole, increasing in speed until it is flowing at the speed of light at the Schwarzchild radius

is flowing into the black hole, increasing in speed until it is flowing at the speed of light at the Schwarzchild radius

Deuterium is a form of hydrogen with both a proton and a neutron in the nucleus, instead of just a proton. Helium-3 has one fewer neutron than the more common Helium-4. Therefore, Deuterium and Helium-3 are of _____ hydrogen and helium, respectively.

isotopes

The stellar wind from a Mira variable is strong because ______.

its surface gravity is weak

If you measured the parallax of a star from Mars instead of from Earth, you would expect the angle to be ______.

larger

The energy emitted by an isolated white dwarf comes from ______.

leftover heat

In the proton-proton chain, ______.

less than 1% of the total mass is converted into energy

Energy is released when three helium nuclei are fused into a carbon nucleus because the carbon nucleus has _____ total mass.

less, smaller, or lower

The plot shown in the image is an example of a(n) ______.

light curve

In terms of the wide range of stellar masses, Earth's Sun is considered a _____ mass star.

low

Match the types of variable stars and their properties to the type of star that might experience this phase late in its life.

low-mass-RR Lyrae low-mass-variation over hours or days high-mass-Cepheid high-mass-variation over weeks or months

A brighter star will have a ______ number for its apparent magnitude, compared to a dimmer star.

lower

A more luminous star will have a ______ number as its absolute magnitude, compared to a less luminous star.

lower

Compared to the density of a young low-mass star in hydrostatic equilibrium, the density for a young high-mass star, which has a higher rate of energy production, will be ______.

lower

Astronomers try to find the distances to stars using methods such as parallax or the properties of variable stars because a distance and the easily measured brightness can be used to find the star's _____.

luminosity

As a star moves from A to B to C, its ______.

luminosity increases and temperature decreases

Extremely high-mass stars do not form easily because of their very high _____.

luminosity, temperature, pressure, or heat

In the H-R diagram, the vertical axis is ______ and the horizontal axis is ______.

luminosity; surface temperature

A pulsar with a strong magnetic field and that emits bursts of X rays and gamma rays is called a _____.

magnetar

Much of the structure in the Sun's atmosphere can be explained by the interaction of gas with the Sun's ______ field.

magnetic

Most of the activity in the Sun's corona is a direct result of ______.

magnetic fields

The diagonal line of stars indicated by the arrows in the diagram is the ______.

main sequence

A white dwarf is held up by electron degeneracy pressure (meaning that the exclusion principle limits how closely electrons can be packed). If accretion adds to the white dwarf's gravitational energy, adding matter will _______.

make it shrink

Prominences are ______. (Select all that apply.)

many times the size of Earth cooler than the surrounding gas large loops of plasma

The factor that has the greatest effect on a star's lifetime and evolution is its ______.

mass

The final stage in a star's life is determined by its _____ when it forms.

mass

To become a black hole, a star must be ______.

massive

The Maunder minimum ______. (Select all that apply.)

may link sunspot activity with the Earth's climate occurred between approximately 1650 and 1710 coincided with a time when the Earth was cooler than normal was a period of low sunspot activity

Material ejected from a supernova ______. (Select all that apply.)

may trigger the collapse of clouds, forming new stars increases the abundance of heavier elements in the interstellar medium seeds clouds that form new stars

The primary mission of the Hipparcos satellite was to ______.

measure the parallaxes of stars

Compared to a low-mass star that might become an RR Lyrae variable for a few million years as it passes through the instability strip on the H-R diagram, a high-mass star ______. (Select all that apply.)

might be a variable more than once will change luminosity over a longer period can become a Cepheid variable

A set of calculations or simulations including the relevant physics for a star is called a stellar _____.

model

Since astronomers cannot make direct measurements of the conditions inside a star, they develop a detailed stellar _____ that allows them to make predictions for quantities that can be observed, such as total luminosity, neutrino counts, or stellar radius.

model

A star at point A will take (a) _____ time to reach the main sequence than one at point B.

more, longer, or greater

As a result of the selection effect from the brightness-distance equation, when you look up at the night sky, ______.

most of the stars you see are highly luminous ones

Compared to the time for a solar-mass star to move from the main sequence to the red giant stage, a 20 M☉ star will take ______.

much less time

Compared to a star like the Sun, the time for a 5 M☉ star to complete the pre-main-sequence stage is ______.

much shorter

In a binary star system, the period of each star's orbit ______.

must be the same

At the end of a massive star's life, the remains of the core are too massive to form a white dwarf. Instead, a denser _____ star will be formed.

neutron

An isotope is a form of an element that has a different number of ______ than usual.

neutrons

A star generates energy in its core through the process of ______.

nuclear fusion

Convection in a massive star ______. (Select all that apply.)

occurs only near the core brings unburned hydrogen down to the core

A star will spend most of its lifetime ______.

on the main sequence

Applying conservation of angular momentum (MVR = constant), if a star contracts to half of its radius, it will complete one rotation in ______ as much time.

one-quarter

At 0.5 solar radii from the core of the Sun, the temperature is about _____ that of the core.

one-quarter

A star cluster forming out of a molecular cloud would mostly like be a(n) ______.

open cluster

The figure demonstrates the concept behind the measurement of distance using the method of _____.

parallax

Sunspots are ______. (Select all that apply.)

places where flares occur about 1300 K cooler than the rest of the surface indicators of solar activity

The matter a low-mass star ejects near the end of its life, shown in the image, is called a ______.

planetary nebula

The image shows a ______. (Select all that apply.)

pre-main-sequence star bipolar outflow

Looking at pictures of the sky, you notice that over the course of two years, the position of a particular star compared to the background stars shifts several arcseconds. The motion is in a straight line. What is the name astronomers use for such motion?

proper motion

The shift in a star's position on the sky caused by the motion of the star in the Milky Way is called ______.

proper motion

To calculate the transverse velocity of a star through space (in km/sec), you would first need to know its ______. (Select all that are required.)

proper motion distance

A rapidly rotating neutron star that emits radio or X-ray pulses is called a(n) _____.

pulsar

Gamma-ray bursts were discovered accidentally, in 1967, by satellite telescopes looking for ______.

radiation from nuclear bombs

The green diagonal lines plotted on this H-R diagram were created by applying the Stefan-Boltzmann law. The lines indicate combinations of luminosity and temperature such that stars on a given line have the same ______.

radius

A star moving on the line from point D to C is (has) ______.

reached the end of its life

Coronal holes are ______. (Select all that apply.)

regions of the corona from which the ions and electrons of the solar wind escape regions of the corona that are cooler than average regions of the corona with weaker magnetic fields

Stars on the instability strip in the H-R diagram (see figure) are ______.

regular variables

As a massive star moves from the main sequence to its helium burning stage, its luminosity ______.

remains almost the same

Right when a star experiences a helium flash, as seen from outside its luminosity ______.

remains the same

Compared to a low-mass star, a high-mass star's lifetime will be ______.

shorter

The figure shows a representation of space near a black hole. The distortion downward from the flat plane would best be explained as ______.

showing with the perpendicular direction how much farther an object would travel "forward" to the black hole than if space were not distorted

The event shown in this ultraviolet image of the Sun is a ______.

solar flare

Jets or plumes of material sticking up from the Sun's surface that are common in images of the chromosphere are called ______.

spicules

The overall trend (not the spikes) shown in the graph of pulsar rotation speed over time is known as ______.

spindown

The radio radiation produced by a pulsar is caused by ______.

spiraling charges in a magnetic field

If star A has a parallax twice as much as star B, you can conclude that ______.

star A is half as far as star B

You determine through spectroscopy that two stars are both a specific kind of standard candle. If the brightness of star A is 100 times the brightness of star B, then ______.

star B is 10 times farther away

You determine through spectroscopy that two stars are both a specific kind of standard candle. If the brightness of star Gamma is four times the brightness of star Delta, then ______.

star Gamma is half as far away

The prominence of the main sequence on an H-R diagram is easily explained by the fact that ______.

stars spend 90% of their time on the main sequence

The tidal force near a small black hole will be _____ than near a large black hole.

stronger, larger, greater, higher, or more

Astronomers usually study black holes by ______. (Select all that apply.)

studying the X-ray spectra of accretion disks studying the light curves of accretion disks direct imaging of jets of material expelled by the black hole

The image shows a

sunspot

The figure shows how a pair of _____ are created by the Sun's magnetic field.

sunspots

The image shows an example of a ______.

supernova remnant

Charges accelerated in a magnetic field, spiraling along the field lines, emit radio waves over a broad and continuous span of wavelengths. This emission is called _____ radiation. (Hint: This is a kind emitted by pulsars.)

synchrotron

The Stefan-Boltzmann law tells us that for two stars of the same size, the more luminous one has a higher ______.

temperature

The variations in stellar spectra shown in this image are primarily a result of differences in the _____ of the stars.

temperatures

Mira variable stars's radiation pressure and pulsations create a stellar wind ejecting about 10-4 M☉ per year with matter flowing into space at a rate of ______ of kilometers per second.

tens

Differential rotation requires ______. (Select all that apply.)

that the composition of a body must be fluid that different parts of a rotating body have different rotational periods

To determine the diameter of stars using the light curve of an eclipsing binary, astronomers measure ______.

the Doppler shifts of the stars the duration of the eclipse how long it takes for the light to dim to full eclipse

Millisecond pulsars are typically found in binary systems because ______.

the companion provides the matter that spirals onto the neutron star

When fusion is unable to supply further energy in a massive star, ______.

the core collapses, and the outer layers collapse onto it

Different colors in a visible light picture of a planetary nebula (as shown) are primarily a result of variations in ______.

the elements that are radiating

We see pulsed beams of radiation from pulsars because ______. (Select all that apply.)

the magnetic poles of the neutron star are offset from the rotation axis the accelerated electrons cannot move far from the strong magnetic fields at the magnetic poles

The center of mass of a system of two objects (such as stars) is always closest to ______.

the more massive object

When variable stars expand, ______.

the outer layers decrease in density and are able to release trapped radiation

If the core of a giant star is so densely packed that the electrons become degenerate, it will simply rise in temperature as nuclear reactions continue until it is hot enough to start the next fusion reaction. This is mostly because ______.

the pressure does not depend on the temperature, so it does not expand and cool

Photons escape from a star when ______.

the probability of interacting with matter becomes very low

The pressure of the hot gas in the Sun holds it up against gravitational collapse. If the Sun were more massive, we could conclude that ______.

the product of the temperature and density inside the Sun would be higher

Pulsars gradually slow down, a process known as "spindown." This happens because ______. (Select all that apply.)

the pulsar is losing energy as it emits radiation the particles accelerated by the pulsar exert a reaction force on it

The Schwarzschild radius is ______. (Select all that apply.)

the radius at which an object would become a black hole the radius at which the escape velocity equals the speed of light

To use the modified form of Kepler's third law to determine the sum of the masses of a pair of stars, astronomers need to measure or know ______. (Select all that are needed.)

the semimajor axis (separation) of the orbit the orbital period

Any concentration of mass becomes a black hole when its escape velocity equals ______.

the speed of light

Because of the aberration of starlight, a telescope must be tilted slightly compared to the direct line to a distant star. This is necessary because ______. (Select all that apply.)

the speed of light is finite the Earth is moving

A star is cooler as a red giant than when it was on the main sequence because ______.

the star has expanded in volume

Absorption lines in main-sequence stars (luminosity class V) are wider than the lines in supergiants (class I). Wider lines occur when the atoms producing them collide more frequently. The difference can be explained because ____.

the surfaces of main-sequence stars are denser

As you examine stars along the main sequence from red (M type) to blue (O type), ______. (Select all that apply.)

their radius increases their mass increases

Stars in open clusters and associations spread out over time primarily because ______.

there are not enough of them to hold the cluster together by gravity. Random and orbital motions separate them

Beta and Alpha Centauri appear larger than other stars in this image because _______.

these stars have higher apparent brightness than other stars

Gamma-ray bursts were difficult to understand because ______. (Select all that apply.)

they are not predictable gamma rays are so energetic that they are difficult to focus they appear all over the sky

The key factor that keeps bodies smaller than about 0.1 M☉ from entering the main sequence is that ______.

they are too low in mass to sustain hydrogen fusion

Astronomers believe objects such as Cygnus X-1, a binary system of a B supergiant and an unseen companion, are black holes because ______.

they can measure the combined mass of the system and calculate the mass of the unseen companion (if they know the type of the star)

Millisecond pulsars emit thousands of pulses per second. This happens because ______.

they have been sped up to high rotation speeds by gas that spiraled down to hit their surface

Solar neutrinos are difficult to detect because ______.

they interact very weakly with matter

A spectrum shows the intensity of light as a function of wavelength. A light curve shows the intensity of light (at one or many wavelengths) as a function of _____.

time

By using Kepler's laws, you can determine the relative distances of the planets in astronomical units (AU). Then you can determine the value of the AU in kilometer by ______. (Select all that apply.)

timing a radar signal bounced off of Venus using triangulation to measure the distance to Mars

The connection between neutron-star mergers and bright events known as kilonovas was established because ______.

unique waves from such mergers have been detected and localized by gravity wave experiments

Fusion of an oxygen atom and a helium nucleus requires much higher _____ than the proton-proton chain, so that the much greater electrical repulsion of the nuclei can be overcome.

velocities, temperatures, or speeds

High _____ are necessary for fusion so that the electrical repulsion of the nuclei can be overcome.

velocities, temperatures, pressures, or speeds

Red giant stars are ______. (Select all that apply.)

very large orange or red in color relatively cool for stars

Hawking radiation is emitted by a black hole in the form of a pair of photons known as ______.

virtual particles

Through your telescope, two stars appear near each other. After taking images of them for a decade, you are able to make a nifty animation that shows them orbiting each other. Since you can see the stars, you have studied a(n) binary.

visual

Select two answers to fill in the blanks: At the highest surface temperature of stars, you expect the Balmer absorption lines in stellar spectra to become ______ because most of the electrons are already ______.

weaker, above the n = 2 orbital

After a star's outer layer is shed as a planetary nebula, the remaining exposed core is a ______.

white dwarf

When a low-mass star ejects a planetary nebula, the remnant that remains is a ______.

white dwarf

All Type Ia supernovae are about the same intensity, 10^10 L☉, because ____.

white dwarfs that explode are all the same mass

Over time, the temperature of an isolated white dwarf ______.

will steadily decrease as it shines

If the Sun were instantaneously replaced by a 1 solar mass black hole, the planets ______.

would mostly continue in their orbits the same as usual

The triple alpha process occurs in ______.

yellow giants