Stars & Galaxies Test 3
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103 Terms
A white dwarf is __________.
a brown dwarf that has exhausted its fuel for nuclear fusion
an early stage of a neutron star
a precursor to a black hole
what most stars become when they die
what most stars become when they die
3.A typical white dwarf is __________.
as massive as the Sun but only about as large in size as Earth
as large in diameter as the Sun but only about as massive as Earth
as massive as the Sun but only about as large in size as Jupiter
about the same size and mass as the Sun but much hotter
as massive as the Sun but only about as large in size as Earth
4.The maximum mass of a white dwarf is ___________.
about 1.4 times the mass of our Sun
about 3 times the mass of our Sun
limitless; there is no theoretical limit to the maximum mass of a white dwarf
about the mass of our Sun
about 1.4 times the mass of our Sun
What is an accretion disk?
a disk of material found around every white dwarf in the Milky Way Galaxy
any flattened disk in space, such as the disk of the Milky Way Galaxy
a stream of gas flowing from one star to its binary companion star
a disk of hot gas swirling rapidly around a white dwarf, neutron star, or black hole
a disk of hot gas swirling rapidly around a white dwarf, neutron star, or black hole
6.According to our modern understanding, what is a nova?
the explosion of a massive star at the end of its life
an explosion on the surface of a white dwarf in a close binary system
a rapidly spinning neutron star
the sudden formation of a new star in the sky
an explosion on the surface of a white dwarf in a close binary system
What would happen if a white dwarf gained enough mass to reach the 1.4 solar-mass white dwarf limit?
The white dwarf would collapse in size, becoming a neutron star.
The white dwarf would collapse to become a black hole.
The white dwarf would undergo a nova explosion.
The white dwarf would explode completely as a white dwarf supernova.
The white dwarf would explode completely as a white dwarf supernova.
A neutron star is __________.
the remains of a star that died by expelling its outer layers in a planetary nebula
an object that will ultimately become a black hole
a star made mostly of elements with high atomic mass numbers, so that they have lots of neutrons
the remains of a star that died in a massive star supernova (if no black hole was created)
the remains of a star that died in a massive star supernova (if no black hole was created)
A typical neutron star is more massive than our Sun and about the size (radius) of __________.
Jupiter
a small asteroid (10 km in diameter)
the Moon
Earth
a small asteroid (10 km in diameter)
Which of the following statements about electron degeneracy pressure and neutron degeneracy pressure is true?
The life of a white dwarf is an ongoing battle between electron degeneracy pressure and neutron degeneracy pressure.
Electron degeneracy pressure is the main source of pressure in white dwarfs, while neutron degeneracy pressure is the main source of pressure in neutron stars.
In a black hole, the pressure coming from neutron degeneracy pressure is slightly greater than that coming from electron degeneracy pressure.
Both electron degeneracy pressure and neutron degeneracy pressure help govern the internal structure of a main-sequence star.
Electron degeneracy pressure is the main source of pressure in white dwarfs, while neutron degeneracy pressure is the main source of pressure in neutron stars.
Pulsars are thought to be __________.
accreting white dwarfs
rapidly rotating neutron stars
accreting black holes
unstable high-mass stars
rapidly rotating neutron stars
How is an x-ray burst (in an x-ray binary system) similar to a nova?
Both typically recur every few hours to every few days.
Both involve explosions on the surface of stellar corpse.
Both result in the complete destruction of their host stars.
Both are thought to involve fusion of hydrogen into helium.
Both involve explosions on the surface of stellar corpse.
What is the basic definition of a black hole?
a compact mass that emits no visible light
any object made from dark matter
an object with gravity so strong that not even light can escape
a dead star that has faded from view
an object with gravity so strong that not even light can escape
What do we mean by the event horizon of a black hole?
It is the point beyond which neither light nor anything else can escape.
It is the place where x-rays are emitted from black holes.
It is the center of the black hole.
It is the distance from the black hole at which stable orbits are possible.
It is the point beyond which neither light nor anything else can escape.
What do we mean by the singularity of a black hole?
It is the “point of no return” of the black hole; anything closer than this point will not be able to escape the gravitational force of the black hole.
The term is intended to emphasize the fact that an object can become a black hole only once, and a black hole cannot evolve into anything else.
It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions.
It is the edge of the black hole, where one could leave the observable universe.
It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions.
The Schwarzschild radius of a black hole depends on __________.
both the mass and chemical composition of the black hole
the way in which the black hole formed
the observationally measured radius of the black hole
only the mass of the black hole
only the mass of the black hole
When a proton and an antiproton collide
one of the protons is converted to an electron and they form a hydrogen atom.
they destroy each other and produce energy in the form of gamma rays.
one proton is converted to a neutron and the other is converted to an electron.
A proton and an antiproton can not collide because the Coulomb barrier is too great.
one of the protons is converted to a neutron and they form nucleus of one proton and one neutron.
they destroy each other and produce energy in the form of gamma rays.
What are some theories regarding the source of gamma-ray bursts?
Energy levels from gamma ray bursts being in the neighborhood of half a teraelectronvolt or less
Rapidly moving material colliding and generating shock waves
Neutron star collisions, mergers between neutron stars and black holes, and the collapse of a massive star into a black hole
High-energy gamma rays resulting from collisions between electrons
Neutron star collisions, mergers between neutron stars and black holes, and the collapse of a massive star into a black hole
What is the most common source of the recurrent X-ray burst phenomena?
Merger of black holes
Collapse of a massive star into a black hole
The accretion of material on the surface of a neutron star in a binary system, triggering thermonuclear explosions on that surface.
Merger of neutron stars
The accretion of material on the surface of a neutron star in a binary system, triggering thermonuclear explosions on that surface.
Suppose two neutron stars or two black holes are closely orbiting one another. What do scientists predict will eventually happen to them, and why?
Their orbits will gradually grow larger because of the centrifugal force involved as they circle around each other.
Their orbits will spiral inward as a result of friction with the surrounding gas until all the gas clears, after which their orbits will remain stable.
Their orbits will spiral inward until the two objects merge because of energy lost through gravitational waves.
The orbits would remain stable unless there were a third object orbiting along with them.
Their orbits will spiral inward until the two objects merge because of energy lost through gravitational waves.
When did scientists first detect gravitational waves from mergers of compact objects (pairs of neutron stars or black holes)?
Gravitational waves have not yet been detected, though scientists hope to detect them soon.
2015
1990
1543
2015
How does the diameter of the disk of the Milky Way Galaxy compare to its thickness?
The diameter is about 10 times as great as the thickness.
The diameter and thickness are roughly equal.
The diameter is about 100,000 times as great as the thickness.
The diameter is about 100 times as great as the thickness.
The diameter is about 100 times as great as the thickness.
What do we call the bright, sphere-shaped region of stars that occupies the central few thousand light-years of the Milky Way Galaxy?
the galaxy’s halo
the galaxy’s bulge
the galaxy’s disk
a globular cluster
the galaxy’s bulge
The Sun’s location in the Milky Way Galaxy is __________.
in the halo of the galaxy, about 27,000 light-years above the galactic disk
near the galactic center
in the galactic disk, roughly halfway between the center and the outer edge of the disk
at the outer edge of the galactic disk
in the galactic disk, roughly halfway between the center and the outer edge of the disk
What are the Magellanic Clouds?
two nebulae located in the disk of the Milky Way galaxy and visible only from the Southern Hemisphere
the clouds of dust and gas found interspersed in many places throughout the Milky Way Galaxy
two small galaxies that orbit the Milky Way Galaxy
star-forming clouds found in the constellation Orion
two small galaxies that orbit the Milky Way Galaxy
How do disk stars orbit the center of the galaxy?
They all orbit in roughly the same plane and in the same direction.
They follow orbits that move up and down through the disk, typically taking them about 50,000 light-years above and below the disk on each orbit.
They follow spiral paths along the spiral arms.
They have orbits randomly inclined and in different directions relative to the galactic center.
They all orbit in roughly the same plane and in the same direction.
How do we know the total mass of the Milky Way Galaxy that is contained within the Sun’s orbital path?
by estimating the amount of gas and dust in between the stars
by using the law of conservation of angular momentum to calculate the orbital speeds of nearby stars
by counting the number of stars visible in this region of the galaxy
by applying Newton’s version of Kepler’s third law (or the equivalent orbital velocity formula) to the Sun’s orbit around the center of the Galaxy
by applying Newton’s version of Kepler’s third law (or the equivalent orbital velocity formula) to the Sun’s orbit around the center of the Galaxy
Elements heavier than hydrogen and helium constitute about _____ of the mass of the Milky Way’s interstellar medium.
0.002 %
98%
2 %
70 %
2 %
What do we mean by the star-gas-star cycle?
It describes the orbits of the stars and interstellar medium around the center of the galaxy.
It is the set of nuclear reactions by which heavy elements are produced in the cores of massive stars.
It is the continuous recycling of gas in the galactic disk between stars and the interstellar medium.
It is the idea that stars in close binary systems can exchange gas with one another.
It is the continuous recycling of gas in the galactic disk between stars and the interstellar medium.
The primary way that we observe the atomic hydrogen that makes up most of the interstellar gas in the Milky Way is with __________.
space-based ultraviolet telescopes
ground-based visible-light telescopes
radio telescopes observing at a wavelength of 21 centimeters
x-ray telescopes
radio telescopes observing at a wavelength of 21 centimeters
Which of the following models best explains why our galaxy has spiral arms?
No model can explain the existence of the arms, which rotate with the galaxy like the fins of a giant pinwheel toy.
The spiral arms are composed of groups of stars that are bound together by gravity and therefore always stay together as the galaxy rotates.
The spiral arms were imprinted on the galaxy at its birth.
Ever since, like a coiling rope, the spiral arms have been wound tighter with each galactic rotation.
The spiral arms are a wave of star formation caused by a wave of density propagating outward through the disk of the galaxy.
The spiral arms are a wave of star formation caused by a wave of density propagating outward through the disk of the galaxy.
Most stars in the Milky Way’s halo are _________.
very old
blue or white in color
found inside molecular clouds
very young
very old
What is an ionization nebula?
a clump of gas that will soon give birth to a new star
a region of hot, low-density gas surrounding a recent supernova
a colorful cloud of gas that glows because it is heated by light from nearby hot stars
a name sometimes used to describe spiral galaxies besides the Milky Way
a colorful cloud of gas that glows because it is heated by light from nearby hot stars
Where does most star formation occur in the Milky Way Galaxy?
in the central bulge
in the spiral arms
within the halo
everywhere throughout the galactic disk
in the spiral arms
36.
What produces the 21-cm line that we use to map out the Milky Way Galaxy?
Read this to me
molecular hydrogen
helium
carbon monoxide
ionized hydrogen
atomic hydrogen
atomic hydrogen
37.
What do halo stars do differently from disk stars?
Halo stars remain stationary, quite unlike disk stars that orbit the galactic center.
Halo stars orbit the galactic center with many different inclinations, while disk stars all orbit in nearly the same plane.
Halo stars orbit the center of the galaxy at much lower speeds than disk stars.
Halo stars explode as supernovae much more frequently than disk stars.
Halo stars orbit the galactic center with many different inclinations, while disk stars all orbit in nearly the same plane.
What kind of object do we think lies in the center of the Milky Way Galaxy?
an enormous collection of dark matter, explaining why we detect no light at all from the galactic center
a dense cluster of young, hot stars
a black hole of about 4 million solar masses
a gigantic x-ray binary system
a black hole of about 4 million solar masses
The energy source at the center of our galaxy
is not visible at optical wavelengths.
produces X-rays.
must be less than 10 AU in diameter.
all of the above.
none of the options.
all of the above.
The age of the Milky Way galaxy has been estimated to be at least 13 billion years based on
the energy produced by Sagittarius A*.
21-cm radiation from H I regions.
observations of globular clusters.
observations of open clusters.
the rotation curve of the galaxy.
observations of globular clusters.
Based on the number of galaxies visible in the Hubble eXtreme Deep Field, the estimated number of galaxies in our observable universe is at least _____.
100 million
100 billion
infinity
50,000
100 billion
Which of the following is not one of the three major categories of galaxies?
globular galaxies
irregular galaxies
elliptical galaxies
spiral galaxies
globular galaxies
4 Galaxies with disks but no evident spiral arms are called __________.
elliptical galaxies
lenticular galaxies
irregular galaxies
barred spiral galaxies
lenticular galaxies
On a graph plotting galaxy luminosities against galaxy colors, the red sequence represents galaxies that are __________ than galaxies of the blue cloud.
hotter and less luminous
smaller and more irregular in shape
more likely to have spiral shapes
larger and more elliptical
larger and more elliptical
Which of the following best describes the status of the Milky Way in our Local Group of galaxies?
It is one of the two largest galaxies in the group.
It is one of about a dozen large spiral galaxies in the group.
It is quite average among the galaxies in the group.
It is by far the largest galaxy in the group.
It is one of the two largest galaxies in the group.
A standard candle is __________.
a light source of known luminosity
another name for a barred-spiral galaxy
a 7-cm-long wax candle
another name for a main-sequence star
a light source of known luminosity
What is a Cepheid variable?
It is a type of luminous star that makes an excellent standard candle.
It is a type of galaxy that varies in its light output.
It is a bright source of variable x-ray emission, thought to harbor a supermassive black hole.
It is a main-sequence star of spectral type B5.
It is a type of luminous star that makes an excellent standard candle.
As described by Leavitt’s law, what two observable properties of a Cepheid variable are directly related to one another?
the period between its peaks of brightness and its luminosity
the period between its peaks of brightness and its distance
its mass and its distance
its luminosity and its mass
the period between its peaks of brightness and its luminosity
10.How did Harlow Shapley use the period-luminosity relationship of RR Lyrae variables to determine the size and center of the Milky Way galaxy?
He found the distances to individual variables free floating in the halo.
He found the distances to open clusters found throughout the disk of the galaxy.
He found the distances to globular clusters distributed about the center of the galaxy.
He determined the proper motion of globular clusters in the outer disk of the galaxy.
Shapley found the distances to globular clusters distributed about the center of the galaxy.
What does Hubble’s law tell us?
For every force, there is an equal and opposite reaction force.
The more distant a galaxy, the faster it is moving away from us.
The faster a spiral galaxy’s rotation speed, the more luminous it is.
The longer the period of a Cepheid variable, the greater its luminosity.
The more distant a galaxy, the faster it is moving away from us.
What two quantities did Edwin Hubble plot against each other to discover the expansion of the Universe?
velocity and temperature
luminosity and temperature
luminosity and distance
age and distance
velocity and distance
velocity and distance
13.
Given that white dwarf supernovae are such good standard candles, why don’t we use them to measure the distance to all galaxies?
Read this to me
They can occur only in spiral galaxies, not elliptical galaxies.
We cannot see them beyond a distance of about 100 million light-years.
They are rare events, so we have observed them in only a tiny fraction of all galaxies.
We would, but we don’t have enough telescopes.
They are rare events, so we have observed them in only a tiny fraction of all galaxies.
When we use an analogy that represents the expanding universe with the surface of an expanding balloon, what does the inside of the balloon represent?
The entire universe
The center of the universe
Regions of the universe beyond the Milky Way Galaxy
The inside of the balloon does not represent any part of our universe
The inside of the balloon does not represent any part of our universe
If we say that a galaxy has a lookback time of 1 billion years, we mean that __________.
it is 400 million years old
it was 1 billion light-years away when the light left the galaxy
it is now 1 billion light-years away
its light traveled through space for 1 billion years to reach us
its light traveled through space for 1 billion years to reach us
Cosmological redshift is the result of __________.
old, red stars in distant galaxies
the high speeds at which galaxies move within clusters
supermassive black holes
the expansion of the universe
the expansion of the universe
Current estimates place the age of the universe at about __________.
4 1/2 billion years
10 billion years
10 million years
14 billion years
14 billion years
18.
Which of the following sequences lists the methods for determining distance in the correct order from nearest to farthest?
main-sequence fitting, parallax, Hubble's law, Tully-Fisher relation, white-dwarf supernovae
parallax, main-sequence fitting, Tully-Fisher relation, white-dwarf supernovae, radar ranging
parallax, main-sequence fitting, Cepheid variables, Tully-Fisher relation, Hubble's law
main-sequence fitting, parallax, Cepheid variables, Tully-Fisher relation, Hubble's law
parallax, main-sequence fitting, Tully-Fisher relation, Cepheid variables, Hubble's law
parallax, main-sequence fitting, Cepheid variables, Tully-Fisher relation, Hubble's law
Telescopes designed to study the earliest stages in galactic lives should be optimized for observations in __________.
radio waves
visible light
infrared light
x-rays
infrared light
According to observations, which type of galaxy was much more common when the universe was 2 billion years old than it is today?
spiral galaxies
We can’t say because humans were not alive at that time.
elliptical galaxies
irregular galaxies
irregular galaxies
Collisions between galaxies typically unfold over a period of __________.
thousands of years
several days
several months
hundreds of millions of years
hundreds of millions of years
Why are collisions between galaxies more likely than collisions of stars within galaxies?
Relative to their sizes, galaxies are much closer together than stars.
Galaxies have higher redshifts than stars.
Galaxies travel through space much faster than stars.
Galaxies are much larger than stars.
Relative to their sizes, galaxies are much closer together than stars.
Current understanding holds that a galaxy’s type (spiral, elliptical, or irregular) __________.
is always determined by whether the galaxy is located in a cluster where collisions are likely or outside a cluster where collisions are less likely
is always determined by the angular momentum of the protogalactic cloud that formed it
may either be the result of conditions in the protogalactic cloud that formed it or the result of later interactions with other galaxies
may either be a result of the mass of the protogalactic cloud that formed it or the result of the heavy element abundance in that cloud
may either be the result of conditions in the protogalactic cloud that formed it or the result of later interactions with other galaxies
Which of the following types of protogalactic clouds is most likely to form an elliptical galaxy?
a dense cloud with quite a bit of angular momentum
a very low-density cloud with very little angular momentum
a very massive cloud with any density and a lot of angular momentum
a low-density cloud with quite a bit of angular momentum
a dense cloud with very little angular momentum
a dense cloud with very little angular momentum
Which of the following is not a feature of central dominant galaxies?
They are thought to form through the mergers of smaller galaxies.
They often have multiple galactic nuclei.
They’re found in clusters of galaxies.
They are spiral galaxies.
They are spiral galaxies.
The distinguishing feature of a starburst galaxy is __________.
strong radio emission from “lobes” of material well outside the visible boundaries of the galaxy
a large luminosity compared to the total luminosity of the Milky Way
the presence of an unusually large number of binary star systems containing x-ray bursters
a rate of star formation that may be 100 or more times greater than that in the Milky Way
a rate of star formation that may be 100 or more times greater than that in the Milky Way
The unusually bright centers found in some galaxies are called __________.
active galactic nuclei
starbursts
halos
supermassive black holes
active galactic nuclei
29. According to current understanding, what is a quasar?
any object with an extremely large redshift is called a quasar.
a galaxy with an unusually high rate of star formation
an active galactic nucleus that is particularly luminous
a large galaxy thought to be formed by the merger of several smaller galaxies, typically found in the center of a galaxy cluster
an active galactic nucleus that is particularly luminous
Which of the following observational phenomena is probably not a direct consequence of the presence of a supermassive black hole?
the large numbers of stars found in globular clusters
the radio emission from radio galaxies
the energy output of quasars
the huge jets seen emerging from the centers of some galaxies
the large numbers of stars found in globular clusters
According to the model in which active galactic nuclei are powered by supermassive black holes, the high luminosity of an active galactic nucleus primarily consists of __________.
intense radiation emitted by the black hole itself
light emitted by hot gas in an accretion disk that swirls around the black hole
the combined light of thousands of young, high-mass stars that orbit the black hole
radio waves emitted from radio lobes found on either side of the galaxy we see in visible light
light emitted by hot gas in an accretion disk that swirls around the black hole
Observations have shown that when the mass of the central black hole is large, then __________.
the host galaxy is eventually completely consumed by the black hole
the mass of the halo and disk of the host galaxy is also large
the mass of the bulge of the host galaxy is also large
the galaxy is always a spiral galaxy
the mass of the bulge of the host galaxy is also large
In the distant past, the temperature of the universe was __________.
absolute zero (0 K)
hotter than it is today
cooler than it is today
3 K
hotter than it is today
What is antimatter?
It is a form of matter that has been hypothesized to exist but for which there is not yet any experimental evidence.
It is the material that makes up a complete antiuniverse that is identical to our own except that it is made from antimatter instead of matter.
It is matter that we infer to be in space by its gravitational influence, but that we have not yet identified.
It consists of particles that are just like those of ordinary matter except with opposite properties, such as opposite charge.
It consists of particles that are just like those of ordinary matter except with opposite properties, such as opposite charge.
What happens when a particle of matter meets its corresponding antiparticle of antimatter?
The combined mass of the two particles is completely transformed into energy (photons).
They fuse to make a heavier particle.
They can form a complete atom.
The question makes no sense, because antimatter does not really exist.
The combined mass of the two particles is completely transformed into energy (photons).
Experiments allow physicists today to reproduce (on very small scales) energy and temperature conditions thought to have prevailed in the early universe as far back in time as about __________.
one ten-billionth (10-10) of a second after the Big Bang
10 billion years ago
10-45 seconds after the Big Bang
380,000 years after the Big Bang
one ten-billionth (10-10) of a second after the Big Bang
The four fundamental forces that operate in the universe today are __________.
strong force, weak force, electromagnetic force, and gravity
nuclear force, gravity, electric force, and magnetic force
nuclear force, electromagnetic force, gravity, and tidal force
strong force, weak force, electric force, and magnetic force
strong force, weak force, electromagnetic force, and gravity
What is the significance of Planck time?
Before it, conditions were so extreme that our current understanding of physics is insufficient to predict what might have occurred.
It is the time at which inflation is thought to have occurred.
It is the amount of time required for two protons to fuse to make deuterium.
It is the time when the cosmic microwave background was released.
Before it, conditions were so extreme that our current understanding of physics is insufficient to predict what might have occurred.
In terms of the “eras” that scientists use to describe different times in the history of the universe, we live in the __________.
era of galaxies
Planck era
era of nuclei
era of nucleosynthesis
era of galaxies
What do we mean by the term inflation?
the sudden release of photons when a particle and antiparticle annihilate one another
quantum fluctuations by high speed, relativistic particles in a state of false vacuum that caused disturbances in the space–time continuum leading to the process described in the question to which this answer refers
a sudden and extremely rapid expansion of the universe that occurred in a tiny fraction of a second during the universe’s first second of existence
the expansion of the universe that we still observe today
a sudden and extremely rapid expansion of the universe that occurred in a tiny fraction of a second during the universe’s first second of existence
Which of the following statements correctly summarizes the events in the early universe according to the Big Bang theory?
Forces and various subatomic particles began to appear during the first second after the Big Bang. For reasons not understood, the particles were all made of ordinary matter and none were made of antimatter, thus explaining why we live in a universe made of matter. The particles underwent some fusion for the first 380,000 years after the Big Bang, at which time the first stars were born.
An episode of what we call inflation initiated the event of the Big Bang. Once the Big Bang got underway, particles and forces began to appear one by one. The forces produced protons, which fused to make hydrogen and helium until the universe was about 380,000 years old. Then gravity began to act, turning the hydrogen and helium into galaxies.
The universe began with the forces unified. During the first fraction of a second, the forces separated and there was a brief but important episode of inflation. Subatomic particles of both matter and antimatter then began to appear from the energy present in the universe. Most of the particles annihilated to make photons, but some became protons, neutrons, electrons, and neutrinos. The protons and neutrons underwent some fusion during the first three minutes, thereby determining the basic chemical composition of the universe.
The Big Bang began with the initiation of what we call inflation, which gradually slowed to the current expansion rate of the universe. Forces came to exist for a different reason, having to do with quantum fluctuations in the space–time continuum. Particles came to exist as a result of cracks made when forces froze. Once there were particles, gravity brought them together to make stars, and the stars then turned the particles into hydrogen, helium, and other elements.
The universe began with the forces unified. During the first fraction of a second, the forces separated and there was a brief but important episode of inflation. Subatomic particles of both matter and antimatter then began to appear from the energy present in the universe. Most of the particles annihilated to make photons, but some became protons, neutrons, electrons, and neutrinos. The protons and neutrons underwent some fusion during the first three minutes, thereby determining the basic chemical composition of the universe.
The Big Bang theory is supported by two major lines of evidence that alternative models have not successfully explained. What are they?
(1) the existence and specific characteristics of the observed cosmic microwave background
(2) the observed overall chemical composition of the universe
(1) the universe is expanding
(2) the observed ratio of spiral to elliptical galaxies in the universe
(1) the episode of inflation thought to have occurred in the early universe
(2) the separation of gravity and the other forces at the end of the Planck era
(1) the early universe was hot and dense
(2) we see distant galaxies as they were in the distant past
(1) the existence and specific characteristics of the observed cosmic microwave background
(2) the observed overall chemical composition of the universe
Which of the following observations cannot be explained by the Big Bang theory, unless we assume that an episode of inflation occurred?
The fact that the universe is expanding
the fact that the temperature of the cosmic microwave background is almost the same everywhere
the existence of the cosmic microwave background
the fact that about 25% of the ordinary matter in the universe consists of helium
the fact that the temperature of the cosmic microwave background is almost the same everywhere
Which statement about the cosmic microwave background (CMB) is not true?
It is the result of a mixture of radiation from many independent sources, such as stars and galaxies.
It is thought to be radiation that began its journey to our telescopes when the universe was about 380,000 years old.
With the exception of very small variations, it appears essentially the same in all directions in which we look into space.
Its spectrum has the shape of an essentially perfect thermal radiation spectrum.
It is the result of a mixture of radiation from many independent sources, such as stars and galaxies.
What is the approximate temperature of the universe (as a whole) today?
3000K
300K
The universe cannot be said to have a single temperature.
3K
3K
Why is the cosmic microwave background (CMB) so cold if the early universe was so hot?
The expansion of the universe has redshifted those photons to an effectively cooler temperature.
Enough time has passed for matter in the universe to release enough heat to cool down.
Misleading! The Big Bang was initially hot but the CMB was released from cold material much later on.
The CMB constantly interacts with atoms, which effectively cool down the photons.
The expansion of the universe has redshifted those photons to an effectively cooler temperature.
The critical density of the universe is the __________.
Read this to me
measured average density of matter in the universe
density value at which the total density of matter precisely equals the total density of antimatter
density of matter necessary for stars and galaxies to form
total density of matter and energy needed to give the universe a “flat” geometry (in spacetime)
total density of matter and energy needed to give the universe a “flat” geometry (in spacetime)
Models of the Big Bang that include inflation predict that the overall geometry of the universe should be “flat” (in spacetime). This prediction __________.
has been shown to be incorrect by study of the expansion pattern of the universe
cannot be tested at this time
has been verified by observing the paths of light coming from distant galaxies
agrees with data found by studying the cosmic microwave background
agrees with data found by studying the cosmic microwave background
Whether the universe is open, closed or flat depends on the ____ of the universe.
temperature
rotation rate
density
luminosity
radius
density
Which of the following statements cannot be tested by science today?
Our universe is flat.
The universe is 14 billion years old.
Prior to the Planck time, our universe sprouted from another universe.
The expansion of the universe is now accelerating.
Prior to the Planck time, our universe sprouted from another universe.
As the universe cooled due to its expansion, it eventually reached a temperature of 3,000 K and protons were able to capture and hold electrons to form neutral hydrogen. This process is known as
hydration.
annihilation.
ionization.
isotropy.
recombination.
recombination.
Which of the following best summarizes what we mean by dark matter?
matter consisting of black holes
matter that we have identified from its gravitational effects but that we cannot see in any wavelength of light
matter that may inhabit dark areas of the cosmos where we see nothing at all
matter for which we have theoretical reason to think it exists, but no observational evidence for its existence
matter that we have identified from its gravitational effects but that we cannot see in any wavelength of light
Which of the following best summarizes what we mean by dark energy?
It is the energy of black holes.
It is a name given to whatever is causing the expansion of the universe to accelerate with time.
It is a type of energy that is associated with the “dark side” of The Force that rules the cosmos.
It is the energy contained in dark matter.
It is a name given to whatever is causing the expansion of the universe to accelerate with time.
What is a rotation curve (for a galaxy)?
a graph that shows a galaxy’s mass on the vertical axis and size on the horizontal axis
a curve used to decide whether a star’s orbit places it in the disk or the halo of a spiral galaxy
a precise description of the shape of a single star’s orbit around the center of the Milky Way Galaxy
a graph showing how orbital velocity depends on orbital distance from the center for a spiral galaxy
a graph showing how orbital velocity depends on orbital distance from the center for a spiral galaxy
What is the primary way in which we determine measure the mass distribution of a spiral galaxy?
We construct its rotation curve by measuring Doppler shifts from gas clouds at different distances from the galaxy’s center.
We count the number of stars we can see at different distances from the galaxy’s center.
We look up the mass of the galaxy in the appendix of a textbook or on the internetWe apply Newton’s version of Kepler’s third law to the orbits of globular clusters in the galaxy’s halo.
We calculate its mass-to-light ratio.
We construct its rotation curve by measuring Doppler shifts from gas clouds at different distances from the galaxy’s center.
What do we mean when we say that the rotation curve for the Milky Way Galaxy is “flat”?
Gas clouds orbiting far from the galactic center have approximately the same orbital speeds as gas clouds located further inward closer to the Galactic center.
All the galaxy’s mass is concentrated in its flat, gaseous disk.
The amount of light emitted by stars at different distances is about the same throughout the galaxy.
The disk of a spiral galaxy is quite flat rather than spherical like the halo.
Gas clouds orbiting far from the galactic center have approximately the same orbital speeds as gas clouds located further inward closer to the Galactic center.
Although we know less about dark matter in elliptical galaxies than in spiral galaxies, what does current evidence suggest?
Unlike the broad distribution of dark matter in spiral galaxies, elliptical galaxies probably contain dark matter only near their centers.
Elliptical galaxies probably contain far more dark matter than spiral galaxies.
Elliptical galaxies probably contain far less dark matter than spiral galaxies.
Elliptical galaxies probably contain about the same proportion of their mass in the form of dark matter as do spiral galaxies.
Elliptical galaxies probably contain about the same proportion of their mass in the form of dark matter as do spiral galaxies.
In general, when we compare the mass of a galaxy or cluster of galaxies to the amount of light it emits (that is, when we look at its mass-to-light ratio), we expect that __________.
Read this to me
the higher amount of mass relative to light (higher mass-to-light ratio), the lower the proportion of dark matter
the amount of light should be at least one solar luminosity for each solar mass of matter (mass-to-light ratio less than or equal to 1)
the higher the amount of mass relative to light (higher mass-to-light ratio), the greater the proportion of dark matter
the higher the amount of mass relative to light (higher mass-to-light ratio), the older the galaxy or cluster
the higher the amount of mass relative to light (higher mass-to-light ratio), the greater the proportion of dark matter
Which of the following is not one of the three major strategies used to measure the mass of a galaxy cluster?
Read this to me
studying x-ray emission from hot gas inside confined by the cluster’s gravitational pull
observing how the cluster gravitationally bends light from galaxies located behind it
measuring the temperatures of stars in the halos of the galaxies
measuring the speeds and positions of galaxies orbiting the cluster’s center
measuring the temperatures of stars in the halos of the galaxies
When we say that a cluster of galaxies is acting as a gravitational lens, what do we mean?
It is an unusually large cluster that has a lot of gravity.
It bends or distorts the light coming from galaxies located behind it.
The overall shape of the cluster is that of a lens.
It magnifies the effects of gravity that we see in the cluster.
It bends or distorts the light coming from galaxies located behind it.
Which of the following best sums up current scientific thinking about the nature of dark matter?
Dark matter consists primarily of a mysterious form of energy that is causing the expansion of the universe to accelerate.
There is no longer any doubt whatsoever that dark matter is made mostly of WIMPs.
Dark matter probably does not really exist, and rather indicates a fundamental problem in our understanding of gravity.
Most dark matter probably consists of weakly interacting particles of a type that we have not yet identified.
Most dark matter probably consists of weakly interacting particles of a type that we have not yet identified.
The primary evidence that has led astronomers to conclude that the expansion of the universe is accelerating comes from __________.
measurements of how galaxy speeds away from the Milky Way have increased during the past century
observations of white dwarf supernovae
observations of the speeds of individual galaxies in clusters
measurements of the rotation curve for the universe
observations of white dwarf supernovae