Astronomy II: Test III (quiz questions, practice questions, test questions)
Summarize the star-gas-star cycle shown in Figure 19.3.
- Stars make new elements by fusion. • Dying stars expel gas and new elements, producing hot bubbles of ionized gas (~106 K). • Hot gas cools, allowing electrons to rejoin their atoms and atomic hydrogen clouds to form (~100-10,000 K). • Further cooling permits molecules to form, making molecular clouds (~30 K). • Gravity forms new stars (and planets) in molecular clouds.
What is a radio galaxy? How can radio galaxies affect the gas surrounding them?
A radio galaxy is a galaxy that has powerful radio luminosity compared to its visible and infrared luminosity from stars. Radio galaxies can emit powerful jets of fast-moving particles that inject high amounts of kinetic energy into their surroundings. The source of the jets are from the accretion of material onto a supermassive black hole. Radio galaxies are AGN seen disk on - so that we can't directly see the center of the galaxy.
What do we mean by a standard candle? Explain how we can use standard candles to measure distances.
A standard candle is a light source of known, "standard" luminosity. Since we know the luminosity, we can use the apparent brightness and the inverse square law for light to determine the object's distance.
What is a starburst galaxy? What do starbursts tell us about the star-gas-star cycle within galaxies?
A starburst galaxy is a galaxy in the present-day universe that is forming stars at a prodigious rate. Starbursts can explain the ages of the stars in some of the small elliptical galaxies in the local group: The large number of supernovae after the first starburst stage created a galactic wind that blew most of the gas out of the galaxy, ending star formation until the gas could cool and reaccumulate within the galaxy for the next starburst. If ellipticals in general experienced a massive starburst episode early in their lives, that could explain the lack of ongoing star formation in ellipticals and why their stars are on average fairly old.
What do we mean by atomic hydrogen gas? How common is it, and how do we map its distribution in the galaxy?
Atomic hydrogen gas is gas that is cool enough for atoms of hydrogen to hold on to their electrons rather than be ionized. Its very common in the interstellar medium. We map its distribution using the light these atoms emit (wavelength = 21cm) when their electrons flip the direction of their spin; 21 cm radiation. Because the wavelength is so long, we must use radio telescopes to observe it.Atomic hydrogen gas clouds are not composed entirely of hydrogen: There is quite a bit of helium and a small amount of other elements in the clouds. Atomic hydrogen gas is spread through the entire galactic disk.
What creates a bubble of hot, ionized gas? What happens to the gas in the bubble over time?
Bubbles of hot, ionized gas are created by supernova explosions and powerful stellar winds of high- mass stars. As the bubbles expand, they create shock fronts in the interstellar medium that drain away their energy. Eventually, the bubbles' expansions slow, the gas cools down, the free electrons rejoin their atoms, and the bubbles merge with interstellar gas.
Describe some of the consequences of galaxy collisions. Why were collisions more common in the past?
Collisions could result in gas being stimulated to form stars. It could also remove gas from galaxies, through tidal interactions, ram pressure events, or (indirectly) by inciting more stellar winds and supernovae. We expect collisions between galaxies to be relatively common (while star-star collisions are rare) because the typical distance between galaxies is comparable in scale to the size of the galaxies themselves. Galaxy collisions should have been even more common in the past than they are today because the density of galaxies was greater in the past. Since a similar number of galaxies (compared to today) existed in closer proximity to each other, they were more likely to encounter each other.
How do the galaxy types found in clusters of galaxies differ from those in smaller groups and those of isolated galaxies?
Elliptical galaxies are much more common in large galaxy clusters than they are among isolated galaxies. Half of the large galaxies in large clusters are ellipticals, while among isolated galaxies they make up only about 15%.
What do we mean by galaxy evolution? How do telescopic observations allow us to study galaxy evolution? How do theoretical models help us study galaxy formation?
Galaxy evolution is the study of how galaxies form and develop in our expanding universe. Telescopic observations allow us to observe the history of galaxies, since the farther we look into the universe, the further we can see back in time. Theoretical modeling helps us study galaxy formation because we cannot see the galaxies before the first stars formed, and the time scales over which galaxies change and interact with each other are much longer than an astronomer's lifetime. Theoretical modeling allows us to test our ideas about how galaxies might have formed and changed over time as they grew more massive (or not) and interacted with other galaxies..
Explain how Hubble proved that the Andromeda Galaxy lies beyond the bounds of the Milky Way.
Hubble was able to see Cepheid variables in the Andromeda Galaxy. When he determined their luminosities from their periods, he was able to find the distance to the Andromeda Galaxy. Since the distance put it far beyond the reaches of our own galaxy, he showed that it must be a separate galaxy.
What is Hubble's law? Explain what we mean when we say that Hubble's constant is between 21 and 23 kilometers per second per million light-years.
Hubble's law states that the speed at which more distant galaxies move away from us is proportional to their distance. The proportionality factor is called Hubble's constant. So when we say that Hubble's constant is between 21 and 23 kilometers per second per million light-years, we mean that for every million light-years of distance away from us, a galaxy's apparent speed away from us increases by 21 to 23 kilometers per second.
How can we use orbital properties to learn about the mass of the galaxy? What have we learned?
If we know a star's orbital period and orbital radius, we can use Newton's version of Kepler's third law to determine the mass of the galaxy, with a warning: We get only the mass of the galaxy within the orbit of the star we examine. What we have learned from our studies to find the distribution of mass in the galaxy is that the stars in the galactic disk orbit at about the same speeds. This observation tells us that most of the galaxy's mass resides far from the center and is distributed throughout the halo. The total mass of the galaxy is 1.5 trillion solar masses.
What are quasars? How are they related to other active galactic nuclei?
Quasars can be hundreds of times more luminous than our galaxy. Their luminosity is emerging from a relatively compact region. Other active galactic nuclei are not as luminous as quasars (which represent the most luminous of these nuclei). But all active galactic nuclei are thought to be powered by accretion onto supermassive black holes.
What is Sgr A*? What evidence suggests that it contains a massive black hole?
Sgr A* is the name of the radio source we find at the center of our galaxy. The orbits of the stars around this object indicate that it contains a few million solar masses of matter within a small space. Observations show that there are not nearly enough stars to account for all of the mass, so we suspect that it contains a supermassive black hole.
What triggers star formation within a spiral arm? How do we think spiral arms are maintained?
Spiral arms are "density waves" that rotate around the center of the galaxy, but they rotate slower than the gas, dust, and stars. So material moves into and out of the density wave/spiral arm. Stars are created more readily in spiral arms because the higher density causes collisions between gas clouds that compresses the gas in the clouds, increasing the strength of gravity and triggering star formation. Spiral arms are maintained because they constantly get new material pulled into the wave, allowing the 'arm' like appearance to continue.
Describe the basic characteristics of stars' orbits in the disk, halo, and bulge of our galaxy.
Stars in the disk of the galaxy have nearly circular orbits that are mostly in the plane of the galactic disk. The disk stars have vertical motions out of the plane, making them appear to bob up and down, but they never get "too far" from the disk. Orbits of stars in the bulge and the halo of the galaxy are much less orderly, traveling around the galactic center on elliptical orbits with more or less random orientations.
What do we mean by a cosmological redshift? How does our interpretation of a distant galaxy's redshift differ if we think of it as a cosmological redshift rather than as a Doppler shift?
The cosmological redshift is the stretching of the wavelength of photons due to the expansion of the universe (or equivalently, decrease in frequency or energy). A Doppler shift is caused by motion toward or away from us. The galaxies are not projectiles in a static universe, as implied by the interpretation of redshift as a Doppler shift; they are being carried along while spacetime itself is expanding. So while redshift and the Doppler shift are sometimes used interchangeably when cosmic distances are small, when they get large, it is important to remember that the redshifts are cosmological in origin, not due to galaxies physically flying about in space.
Distinguish between the disk component and the halo component of a spiral galaxy. Which component includes the cool gas and active star formation?
The disk component of spiral galaxies is a flat disk in which stars follow orderly, nearly circular orbits around the galactic center. The disk contains cool gas and active star formation. The halo component of spiral galaxies has a round shape with stars orbiting at many different inclinations.
How does a galactic fountain help circulate new elements within the Milky Way?
The galactic fountain causes gas from supernova explosions (with lots of heavy elements) to spew from the disk up into the halo. The material eventually falls back down into the disk, mixing with the gas that's already there. This process mixes heavy elements from the supernova explosions with multiple locations in the disk.
What do we mean by the lookback time to a distant galaxy? Briefly explain why lookback times are less ambiguous than distances for discussing objects very far away.
The lookback time to a distant galaxy is the difference between the present age of the universe and the age of the universe when the light left the galaxy. The lookback time is less ambiguous than the distance to a galaxy because in the time that the light has been traveling to us, the universe has expanded, changing the distance to the galaxy, but the time that the photons have been traveling is definite.
What are the starting assumptions for models of galaxy formation? Describe how a spiral galaxy is thought to form.
The starting assumptions used for models of galaxy formation are that the universe was initially filled more or less uniformly with hydrogen and helium gas and that some regions of this gas were slightly denser than others. The extra density in some areas increased the gravitational pull, slowing and then reversing the expansion that occurred due to the cosmological expansion, forming protogalactic gas clouds. The gas cloud begins to form stars, but the star formation does not use up all the gas. The angular momentum of the original gas cloud causes the gas cloud to spin and flatten out as it collapses, gas particles collide, and the gas cools, thereby forming the disk of a spiral galaxy out of the leftover gas. (A system of stars and no gas would not form a disk.)
What are the three major types of galaxies, and how do their appearances differ?
The three major types of galaxies are spirals, ellipticals, and irregulars. Spiral galaxies, like our own, are flat white disks with yellowish bulges in the centers and contain cool gas interspersed with hotter ionized gas. Elliptical galaxies are redder, more rounded, and often football-shaped. They contain very little cool gas and often contain hot, ionized gas. Irregulars do not fit either of the other categories.
Briefly summarize the types of gas present in the disk of the galaxy, and describe how they appear when we view the galaxy in different wavelengths of light.
There are several kinds of gas present in the disk of the galaxy. First, there are hot bubbles, which are composed of low-density, hot, ionized gas (ionized means they have lost at least one electron). This gas is best viewed in the X-ray portion of the spectrum. At lower temperatures we find atomic hydrogen gas (warm and cool). This gas is cool enough to be un-ionized and is best viewed in the radio part of the spectrum, thanks to the 21-centimeter line of atomic hydrogen. Molecular clouds are even cooler than atomic hydrogen, allowing molecules to form. This gas is also best viewed in the radio wavelengths, where we can detect CO molecules using wavelengths of 1.3mm and 2.6mm. Wherever there are CO molecules, there will be lots of H2 molecules as well (molecular hydrogen). The coolest parts of the molecular clouds are the molecular cloud cores that go on to form stars.
A collision between two large spiral galaxies is likely to produce a) a large elliptical galaxy. b) a large spiral galaxy c) one large spiral galaxy and one large elliptical galaxy.
a
Compared to spiral galaxies, elliptical galaxies are a. redder and rounder b. redder and flattened c. bluer and rounder d. bluer and flattened
a
How does the interstellar medium affect our view of most of the galaxy? a. it prevents us from seeing most of the galactic disk wtih visible and ultraviolet light b. it absorbs all wavelengths of light c. it produces so much visible light that it blocks our view of anything beyond it d. it has no effect on visible light observations
a
If we say that a galaxy has a loopback time of 1 billion years, we mean that a. its light traveled through space for 1 billion years to reach us b. is now 1 billion light years away c. it is 400 million years old
a
In stars, helium can sometimes be fused into carbon and heavier elements (in their final stages of life). Why didn't the same fusion processes produce carbon and heavier elements in the early universe? A) By the time stable helium nuclei had formed, the temperature and density had already dropped too low for helium fusion to occur. B) Helium fusion occurred, but the carbon nuclei that were made were later destroyed by the intense radiation in the early universe. C) Temperatures in the early universe were never above the roughly 100 million Kelvin required for helium fusion. D) No one knows—this is one of the major mysteries in astronomy.
a
Observations indicate that galaxies with more massive central black holes tend to also have a) a greater mass of stars in their central bulges. b) a greater overall luminosity. c) a more elliptical shape.
a
Over time, the star-gas-star cycle leads the gas in the milky way to a. have a greater abundance of heavy elements b. have a lower abundance of heavy elements c. become denser and have a greater abundance of heavy elements d. become hotter
a
The four fundamental forces that operate in the universe today are A) strong force, weak force, electromagnetic force, gravity. B) strong force, weak force, electric force, magnetic force. C) nuclear force, electromagnetic force, gravity, tidal force. D) nuclear force, gravity, electric force, magnetic force.
a
We measure the mass of the black hole at the galactic center from a) the orbits of stars in the galactic center. b) the orbits of gas clouds in the galactic center. c) the amount of radiation coming from the galactic center.
a
What are cosmic rays? A) subatomic particles that travel close to the speed of light B) gamma rays and X rays C) fast-moving dust particles in the interstellar medium D) any light waves from space E) lasers used as weapons by extraterrestrials
a
What happened to the quarks that existed freely during the particle era? A) They combined in groups to make protons, neutrons, and their antiparticles. B) They froze out of the soup of particles at the end of the era. C) They evaporated. D) They combined in groups to make electrons and neutrinos. E) They combined in groups to make W and Z bosons.
a
What is a standard candle? a. an object for which we are likely to know the true luminosity b. an object for which we can easily measure the apparent brightness c. a class of object in astronomy that all have exactly the same luminosity d. any star for which we know the exact apparent brightness
a
What is the shape of the Milky Way's halo? a) round like a ball. b) flat like a disk. c) flat like a disk but with a hole in the center.
a
What produces the 21-cm line that we use to map out the Milky Way Galaxy? a. atomic hydrogen b. ionized hydrogen c. molecular hydrogen d. carbon monoxide
a
Which of the following observations cannot be explained by the Big Bang theory unless we assume that an episode of inflation occurred? A) the fact that the temperature of the cosmic microwave background is almost the same everywhere B) the fact that about 25% of the ordinary matter in the universe consists of helium C) the existence of the cosmic microwave background D) the fact that the universe is expanding
a
Compared with stars in the disk, orbits of stars in the halo a. are relatively uniform to each other b. are elliptical, with random orientation c. are elliptical but orbiting in the same direction d. do not have to be around the galactic center
b
Does Hubble's law work well for galaxies in the Local Group? Why or why not? a. no because Hubble did not know the local group existed when he discovered his law b. no because galaxies in the local group are gravitationally bound together c. no because we do not know the precise value of Hubble's constant
b
Galaxies with disks but not evident spiral arms are called a. irregular galaxies b. lenticular galaxies c. barred spiral galaxies d. halo components
b
How did Edwin Hubble measure the distance to the Andromeda Galaxy? a. he measured its parallax b. he applied the period-luminosity relation to Cepheid variables c. he deduced it from its redshift d. he used white dwarf supernovae
b
How many forces operated in the universe during the GUT era? A) one, what we call the "super force" B) two, gravity and the GUT force C) two, gravity and the electroweak force D) three, gravity, the strong force, and the electroweak force E) all of the above forces
b
In principle, if we could see all the way to the cosmological horizon we could see the Big Bang taking place. However, our view is blocked for times prior to about 380,000 years after the Big Bang. Why? A) Before that time, the universe was too crowded with stars. B) Before that time, the gas in the universe was dense and ionized and therefore did not allow light to travel freely. C) Before that time, the universe was dark so there was no light to illuminate anything. D) 380,000 years after the Big Bang marks the time when stars were first born, and thus began to shine the light by which we can see the universe.
b
Spectral lines from Galaxy B are redshifted from their rest wavelengths twice as much as the spectral lines from Galaxy A. According to Hubble's law, what can yous ay about their approximate relative distances? a. Galaxy A is twice as far as Galaxy B b. Galaxy B is four times as far as Galaxy A c. galaxy A is four times as far as Galaxy B d. Galaxy B is twice as far as Galaxy A
b
We determine the distance of a Cepheid in another galaxy by a) measuring its parallax. b) determining its luminosity from the period-luminosity relation and then applying the inverse square law for light. c) knowing that all Cepheids have about the same luminosity and then applying the inverse square law of light.
b
What do we call the bright, sphere-shaped region of stars the occupies the central few thousand light-years of the Milky Way galaxy? a. the galaxy's disk b. the galaxy's bulge c. a globular cluster d. the galaxy's halo
b
What do we mean by inflation? A) what happened the instant after the Big Bang B) a sudden expansion of the universe after the strong force froze out from the GUT force C) the expansion of the universe that we still observe today D) the sudden release of photons when a particle and antiparticle annihilate each other E) the separation that occurs after two photons collide and create a particle and an antiparticle
b
What happens when a particle of matter meets its corresponding antiparticle of antimatter? A) They can form a complete atom. B) The combined mass of the two particles is completely transformed into energy (photons). C) They fuse to make a heavier particle. D) The question makes no sense, since antimatter does not really exist.
b
What is the most accurate way to determine the distance to a nearby star? a. radar ranging b. stellar parallax c. using Cepheid variables d. Hubble's law
b
What is the thickness of the disk of the Milky Way? a. 100 light-years b. 1,000 light-years c. 10,000 light-years d. 100,000 light-years
b
What is the typical percentage (by mass) of elements other than hydrogen and helium in stars that are forming right now in the vicinity of the Sun? a) 20% b) 2% c) 0.02%
b
What kinds of objects lie in the Halo of our galaxy? a. open clusters b. globular clusters c. gas and dust d. o and b stars
b
Where are most heavy elements made? a. in the interstellar medium b. in stars and supernovae c. in the Big Bang, when the universe first began
b
Which of the following is not one of the three major categories of galaxies? a. elliptical galaxies b. globular galaxies c. spiral galaxies d. irregular galaxies
b
Why are Cepheid variables important? a. cepheid variables are stars that vary in brightness because they harbor a black hole b. Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities; Hence, we can use Cepheids as standard candles for distance measurements c. cepheids are a type of young galaxy that helps us understand how galaxies form
b
Why did the era of nuclei end when the universe was about 380,000 years old? A) All the free particles had combined to form the nuclei of atoms. B) The universe had expanded and cooled to a temperature of about 3,000 K, cool enough for stable, neutral atoms to form. C) Neutrinos and electrons were finally able to escape the plasma of the early universe and no longer heated the other particles. D) Photons were finally able to escape the plasma of the early universe and no longer heated the hydrogen and helium ions. E) No theory can explain this.
b
cosmological redshift is the result of a. the high speeds at which galaxies move within clusters b. the expansion of the universe c. very old red stars in distant galaxies d. supermassive black holes
b
which of these galaxies would you most likely find at the center of a large cluster of galaxies? a) a large spiral galaxy b) a large elliptical galaxy c) a small irregular galaxy
b
why can't we see past the cosmological horizon? a. the universe extends only to this horizon b. beyond the cosmological horizon we are looking back to a time before the universe had formed c. we do not have telescopes big enough d. we do not have sensitive enough detectors
b
How are interstellar bubbles made? A) by the collapse of a gas cloud to form stars B) by planetary nebulae from low-mass stars C) by the winds of massive stars and supernovae D) by collisions between galaxies E) by the rapidly rotating magnetic fields of pulsars
c
How do we determine the Milky Way's mass outside the Sun's orbit? a) from the Sun's orbital velocity and its distance from the center of our galaxy b) from the orbits of halo stars near the Sun c) from the orbits of stars and gas clouds orbiting the galactic center at greater distances than the Sun.
c
How do we determine the conditions that existed in the very early universe? A) We look all the way to the cosmological horizon, where we can see the actual conditions that prevailed all the way back to the first instant of the Big Bang. B) The conditions in the very early universe must have been much like those found in stars today, so we learn about them by studying stars. C) We work backward from current conditions to calculate what temperatures and densities must have been when the observable universe was much smaller in size. D) We can only guess at the conditions, since we have no way to calculate or observe what they were.
c
How long after the Big Bang was the Planck time, before which our current theories are completely unable to describe conditions in the universe? A) 10-10 second B) 10-35 second C) 10-43 second D) 3 minutes E) 300,000 years
c
Starburst galaxies are especially bright in a) visible light. b) ultraviolet light. c) infrared light.
c
The disk component of a spiral galaxy includes which of the following parts? a. halo b. bulge c. spiral arms d. globular clusters
c
The luminosity of a quasar is generated in a region the size of a) the Milky Way b) a star cluster. c) the solar system.
c
What can cause a galactic fountain? a. winds and jets from newly-formed protostars b. a supernova occurring in the halo c. multiple supernovae occurring together d. the combined effect of spiral density waves
c
What do we mean by the star-gas-star cycle? a. it is the idea that stars in close binary systems can exchange gas with one another b. it is the set of nuclear reactions by which heavy elements are produced in the cores of stars c. it is the continuous recycling of gas in the galactic disk between stars and the interstellar medium
c
What evidence supports the galactic fountain model? a. we see a jet of ionized gas shooting out of the bulge of our galaxy b. we have mapped several spiral arms of the Milky Way galaxy c. we see hot gas above the disk of the galaxy and cool gas that appears to be raining down from the halo d. we have observed a lot of water molecules in the interstellar medium
c
What evidence supports the theory that there is a black hole in the center of our galaxy? a. we observe an extremely bright x-ray source near the center of our galaxy b. we can see gas falling into an accretion disk and central mass at the center of our galaxy c. the motions of the gas and stars at the center indicates that it contains a million solar masses within a region only about 1 parsec across d. all of the above
c
What is the most accurate way to determine the distance to a nearby galaxy? a. radar ranging b. stellar parallax c. using Cepheid variables d. Hubble's law
c
What kinds of atomic nuclei formed during the era of nucleosynthesis? A) only hydrogen B) only helium C) hydrogen and helium and trace amounts of deuterium and lithium D) roughly equal amounts of each of the following: hydrogen, helium, deuterium and lithium E) nuclei of all the chemical elements
c
What kinds of objects lie in the halo of our galaxy? a. open clusters b. O and B stars c. globular clusters d. gas and dust e. all of the above
c
When we observe a distant galaxy whose photons have travelled for 10 billion years before reaching Earth, we are seeing that galaxy as it was when the universe was about a) 10 billion years old b) 7 billion years old c) 4 billion years old
c
Where are most of the Milky Way's globular clusters found? a) in the disk b) in the bulge c) in the halo
c
Where does most star formation occur in the Milky Way today? a. in the halo b. in the bulge c. in the spiral arms d. in the galactic center
c
Which kind of object is the best standard candle for measuring distances to extremely distant galaxies? a) parallax b) a Cepheid variable star c) a white dwarf supernova
c
Which of the following quasars would you expect to have the largest number of hydrogen absorption lines in its spectrum? a) a quasar with a lookback time of 1 billion years. b) a quasar with a lookback time of 8 billion years. c) a quasar with a lookback time of 13 billion years.
c
Which of these forms of radiation passes most easily through the disk of the Milky Way? a) red light b) blue light c) infrared light
c
Why do virtually all the galaxies in the Universe appear to be moving away from our own? a) We are located near where the Big Bang Happened. b) We are located near the center of the Universe. c) Expansion causes all galaxies to move away from nearly all others.
c
A GUT (grand unified theory) refers to theories that A) unify all four forces. B) unify gravity and the electromagnetic and weak forces. C) unify gravity and the strong and weak forces. D) unify the strong force and the electromagnetic and weak forces. E) unify the electromagnetic and weak forces.
d
A standard candle is a. a 7-cm-long wax candle b. another name for a main-sequence star c. another name for a barred spiral galaxy d. a light source of known luminosity
d
Approximately how long did the era of nucleosynthesis last? A) 10-10 second B) 0.001 second C) 5 seconds D) 5 minutes E) 5 years
d
Based on the results from the Planck satellite, the overall composition of the universe is A) 100% ordinary (baryonic) matter. B) 15% ordinary (baryonic) matter, 85% nonbaryonic dark matter. C) 1% ordinary (baryonic) matter, 99% nonbaryonic dark matter. D) 5% ordinary (baryonic) matter, 26% nonbaryonic dark matter, 69% dark energy.
d
How does the diameter of the disk of Milky Way Galaxy compare to its thickness? a. the diameter and thickness are roughly equal b. the diameter is about 100 times as great as the thickness c. the diameter is about 10 times as great as the thickness d. the diameter is about 100,000 times as great as the thickness
d
Olbers' paradox is an apparently simple question, but its resolution suggests that the universe is finite in age. What is the question? A) What would it be like to ride on a beam of light? B) Can we measure the position and momentum of an electron at the same time? C) How does the Sun produce energy? D) Why is the sky dark at night? E) How many stars are in the universe?
d
The sun's location in the Milky Way galaxy is: a. very near the galactic center b. in the halo of the galaxy. about 28,000 light-years above the galactic disk c. at the very outer edge of the galactic disk d. in the galctic disk, roughly halfway between the center and the outer edge of the disk
d
What do astronomers consider heavy elements? a. elements that are heavier than iron b. elements that are heavier than carbon c. elements taht are heavier than uranium d. all elements beside hydrogen and helium
d
What does Hubble's law tell us? a. the faster a spiral galaxy's rotation speed, the more luminous it is b. the longer the period of a Cepheid variable, the greater its luminosity c. for every force, there is an equal and opposite reaction force d. the more distant a galaxy, the faster it is moving away from us
d
What is the galactic fountain model? a. the idea that there is a lot of interstellar water vapor b. the theory that the milky way is a sprial galaxy and looks like a whirlpool from above c. the theory that hot, ionized gas blows out of the galactic center like a jet or fountain d. the theory that hot, ionized gas blown out of the galactic dis and into the halo by superbubbles cools down and falls back into the disk
d
What makes white-dwarf supernovae good standard candles? a. they are very bright, so they can be used to determine the distances to galaxies billions of light-years away b. they should all have approximately the same luminosity c. they occur so frequently that we can use them to measure the distances to virtually all galaxies d. both A and B
d
Which constellation lies in the direction toward the galactic center? a. Orion b. the big dipper c. leo d. sagittarius
d
Which forces have physicists shown to be the same force under conditions of very high temperature or energy, as confirmed by experiments in particle accelerators? A) gravity and the weak force B) gravity and the strong force C) the strong and weak forces D) the strong and electromagnetic forces E) the electromagnetic and weak forces
e
True or False: stars are continually forming in the halo of our Galaxy today
false
True or False: spiral galaxies have more gas, dust, and younger stars than elliptical galaxies doe
true
True or False: the larger the value of Hubble's constant, the more rapid the expansion of the universe and hence the younger the universe
true
True or false: elliptical galaxies are more likely to be found in clusters than are spiral galaxies
true
True/False: If inflation really occurred, then our observable universe is only a tiny portion of the entire universe born in the Big Bang.
true
True/False: The observed composition of ordinary matter in the universe—roughly 75 percent hydrogen and 25 percent helium—closely matches theoretical predictions based on the Big Bang model.
true
