Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
211 Cards in this Set
- Front
- Back
|
How does a black hole form from a massive star?
|
During a supernova, if a star is massive enough for its gravity to overcome neutron degeneracy of the core, the core will be compressed until it becomes a black hole.
|
|
|
A 10-solar-mass main-sequence star will produce which of the following remnants?
|
neutron star
|
|
|
What causes the radio pulses of a pulsar?
|
As the star spins, beams of radio radiation sweep through space. If one of the beams crosses the earth, we observe a pulse.
|
|
|
Which of the following is closest in mass to a white dwarf?
|
the Sun
|
|
|
What kind of star is most likely to become a white-dwarf supernova?
|
a white dwarf star with a red giant binary companion
|
|
|
A teaspoonful of neutron star material on Earth would weigh
|
more than Mt. Everest.
|
|
|
What is the ultimate fate of an isolated white dwarf?
|
It will cool down and become a cold black dwarf.
|
|
|
After a massive-star supernova, what is left behind?
|
either a neutron star or a black hole
|
|
|
An advanced civilization lives on a planet orbiting a close binary star system that consists of a 15MSun red giant and a 10MSun black hole. Assume that the two stars are quite close together, so that an accretion disk surrounds the black hole. The planet on which the civilization lives orbits the binary star at a distance of 10 AU.
Sometime within the next million years or so, their planet is likely to be doomed because |
the red giant will probably undergo a supernova explosion within the next million years.
|
|
|
Why do astronomers consider gamma-ray bursts to be one of the greatest mysteries in astronomy?
|
because the current evidence suggests that they are the most powerful bursts of energy that ever occur anywhere in the universe, but we don't know how they are produced
|
|
|
How does the gravity of an object affect light?
|
Light coming from a compact massive object, such as a neutron star, will be redshifted.
|
|
|
What is the upper limit to the mass of a neutron star?
|
There is an upper limit less than 3 solar masses, but we do not yet know precisely what it is.
|
|
|
Which of the following best describes what would happen if a 1.5-solar-mass neutron star, with a diameter of a few kilometers, were suddenly (for unexplained reasons) to appear in your hometown?
|
The entire mass of the earth would end up as a thin layer, about 1 cm thick, over the surface of the neutron star.
|
|
|
What kind of pressure supports a white dwarf?
|
electron degeneracy pressure
|
|
|
If you were to come back to our Solar System in 6 billion years, what might you expect to find?
|
a white dwarf
|
|
|
Which of the following statements about novae is not true?
|
Our Sun will probably undergo at least one nova when it becomes a white dwarf about 5 billion years from now.
|
|
|
Which of the following is closest in size (radius) to a neutron star?
|
a city
|
|
|
What is the upper limit to the mass of a white dwarf?
|
1.4 solar masses
|
|
|
From a theoretical standpoint, what is a pulsar?
|
a rapidly rotating neutron star
|
|
|
Why is there an upper limit to the mass of a white dwarf?
|
The more massive the white dwarf, the greater the degeneracy pressure and the faster the speeds of its electrons. Near 1.4 solar masses, the speeds of the electrons approach the speed of light, so more mass cannot be added without breaking the degeneracy pressure.
|
|
|
In some cases, a supernova in a binary system may lead to the eventual formation of an accretion disk around the remains of the star that exploded. All of the following statements about such accretion disks are true except:
|
several examples of flattened accretion disks being "fed" by a large companion star can be seen clearly in photos from the Hubble Space Telescope.
|
|
|
What is the ultimate fate of an isolated pulsar?
|
It will slow down, the magnetic field will weaken, and it will become invisible.
|
|
|
Observationally, how can we tell the difference between a white-dwarf supernova and a massive-star supernova?
|
The spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white-dwarf supernova does not.
|
|
|
Degeneracy pressure is the source of the pressure that stops the crush of gravity in all the following except
|
a very massive main-sequence star.
|
|
|
Suppose a white dwarf is gaining mass because of accretion in a binary system. What happens if the mass someday reaches the 1.4-solar-mass limit?
|
The white dwarf undergoes a catastrophic collapse, leading to a type of supernova that is somewhat different from that which occurs in a massive star but is comparable in energy.
|
|
|
From an observational standpoint, what is a pulsar?
|
an object that emits flashes of light several times per second or more, with near perfect regularity
|
|
|
What do we mean by the singularity of a black hole?
|
It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions.
|
|
|
When we see X rays from an accretion disk in a binary system, we can't immediately tell whether the accretion disk surrounds a neutron star or a black hole. Suppose we then observe each of the following phenomena in this system. Which one would force us to immediately rule out the possibility of a black hole?
|
sudden, intense X-ray bursts
|
|
|
White dwarfs are so called because
|
they are both very hot and very small
|
|
|
Which of the following is closest in size (radius) to a white dwarf?
|
the earth
|
|
|
How do we know that pulsars are neutron stars?
|
No massive object, other than a neutron star, could spin as fast as we observe pulsars spin.
|
|
|
A teaspoonful of white dwarf material on Earth would weigh
|
a few tons.
|
|
|
Which of the following statements about black holes is not true?
|
If the Sun magically disappeared and was replaced by a black hole of the same mass, the earth would soon be sucked into the black hole.
|
|
|
The remnant left behind from a white-dwarf supernova is a neutron star
|
False
|
|
|
Planets have been detected around a pulsar.
|
True
|
|
|
There is no upper limit to the mass of a neutron star.
|
False
|
|
|
All massive-star supernovae leave behind black holes as remnants.
|
False
|
|
|
No visible light can escape a black hole, but things such as gamma rays, X rays, and neutrinos can
|
False
|
|
|
All pulsars are neutron stars, but not all neutron stars are pulsars.
|
True
|
|
|
More massive white dwarfs are smaller than less massive white dwarfs
|
True
|
|
|
Brown dwarfs, white dwarfs, and neutrons stars are all kept from collapsing by degeneracy pressure.
|
True
|
|
|
Neutron stars are the densest objects that we can observe in the universe.
|
True
|
|
|
Light from white dwarfs shows a gravitational redshift.
|
True
|
|
|
How do we learn about what is going on in the center of our own galaxy (the Milky Way)?
|
We cannot see the galactic center with visible or ultraviolet light, but radio and X rays from the center can be detected.
|
|
|
What is a superbubble?
|
a very low-density region of interstellar space, formed by the merger of several bubbles
|
|
|
What are cosmic rays?
|
subatomic particles that travel close to the speed of light
|
|
|
What kinds of objects lie in the halo of our galaxy?
|
globular clusters
|
|
|
How do we know that spheroidal stars are older, on average, than disk stars?
|
There are no blue spheroidal stars
|
|
|
Compared with stars in the disk, orbits of stars in the halo
|
are elliptical, with random orientation.
|
|
|
Why are we unlikely to find Earth-like planets around halo stars in the Galaxy?
|
Halo stars formed in an environment where there were few heavy elements to create rocky planets.
|
|
|
What evidence suggests that the protogalactic cloud that formed the Milky Way resulted from several collisions among smaller clouds?
|
Halo stars differ in age and heavy-element content, but these variations do not seem to depend on the stars' distance from the galactic center.
|
|
|
Approximately how long does it take the Sun to orbit the Milky Way Galaxy?
|
230 million years
|
|
|
What kinds of objects lie in the disk of our galaxy?
|
all of the above
|
|
|
Where are most heavy elements made?
|
in stars and supernovae
|
|
|
What produces the 21-cm line that we use to map out the Milky Way Galaxy?
|
atomic hydrogen
|
|
|
Which of the following statements about globular clusters is false?
|
Globular cluster ages increase with distance from the Milky Way.
|
|
|
The image of our galaxy in radio emission from CO, mapping the distribution of molecular clouds, is closest to the image of our galaxy in
|
infrared emission from interstellar dust grains
|
|
|
Approximately how far is the Sun from the center of the galaxy?
|
28,000 light-years
|
|
|
How does the interstellar medium obscure our view of most of the galaxy?
|
It absorbs visible, ultraviolet, and some infrared light.
|
|
|
Where do most dust grains form?
|
in the winds of red giant stars
|
|
|
Suppose you read somewhere that 10 percent of the matter in the Milky Way is in the form of dust grains. Should you be surprised? If so, why?
|
The 10 percent figure cannot be correct, because dust grains are solid but only about 2 percent of the matter in our galaxy is made of anything besides hydrogen and helium.
|
|
|
What is Sgr A?
|
a source of bright radio emission in the center of our galaxy
|
|
|
What is a shock wave?
|
a wave of pressure that moves faster than the speed of sound
|
|
|
Harlow Shapley concluded that the Sun was not in the center of the Milky Way Galaxy by
|
mapping the distribution of globular clusters in the galaxy
|
|
|
If you were to take a voyage across the Milky Way, what kind of material would you spend most of your time in?
|
warm, rarefied clouds of atomic hydrogen
|
|
|
How are interstellar bubbles made?
|
by the winds of massive stars and supernovae
|
|
|
What do astronomers consider heavy elements?
|
all elements besides hydrogen and helium
|
|
|
What can cause a galactic fountain?
|
multiple supernovae occurring together
|
|
|
What is the galactic fountain model?
|
the theory that hot, ionized gas blown out of the galactic disk and into the halo by superbubbles cools down and falls back into the disk
|
|
|
Which of the following does not accurately describe what we observe toward the Galactic center?
|
at optical wavelengths, we see a cluster of old, red stars
|
|
|
Which constellation lies in the direction toward the galactic center?
|
Sagittarius
|
|
|
Where does most star formation occur in the Milky Way today?
|
in the spiral arms
|
|
|
Compared with our Sun, most stars in the halo are
|
old, red, and dim and have fewer heavy elements
|
|
|
What makes up the interstellar medium?
|
gas and dust
|
|
|
What evidence supports the theory that there is a black hole at the center of our galaxy?
|
The motions of the gas and stars at the center indicate that it contains a million solar masses within a region only about 1 parsec across.
|
|
|
Which of the following statements about the disk of the Milky Way is false?
|
Disk stars are all younger than 5 billion years.
|
|
|
What is the most common form of gas in the interstellar medium?
|
atomic hydrogen
|
|
|
What evidence supports the galactic fountain model?
|
We see hot gas above the disk of the galaxy and cool gas that appears to be raining down from the halo.
|
|
|
How can we see through the interstellar medium?
|
by observing in high-energy wavelengths such as X rays and long wavelengths of light such as radio waves
|
|
|
Sound waves in space
|
travel much faster than sound on Earth but have such low density that they are inaudible
|
|
|
Which of the following statements about halo stars is false?
|
Halo stars are made entirely of hydrogen and helium with no heavy elements
|
|
|
The star-gas-star cycle will continue forever because stars are continually recycling gas
|
False
|
|
|
All heavy elements are made during supernova events.
|
False
|
|
|
Most of the current star formation in the Milky Way occurs in spiral arms.
|
True
|
|
|
Shapley used the distribution of globular clusters in the galaxy to determine that the Sun was not at the center of the Milky Way.
|
True
|
|
|
The Sun is located at the edge of the galaxy, approximately 50,000 light-years from the galactic center.
|
False
|
|
|
Observing the galaxy at radio wavelengths allows us to see beyond the dust in the disk of the galaxy that obscures our view.
|
True
|
|
|
We can see most of the galaxy with visible light.
|
False
|
|
|
Almost all elements heavier than hydrogen and helium were made inside stars.
|
True
|
|
|
Open clusters and young stars are generally found only in the disk of the galaxy and not in the halo.
|
True
|
|
|
Why is the Hyades Cluster important for building up a catalog of the true luminosities of main-sequence stars?
|
It is close enough to us that the distance to the cluster stars can be found by stellar parallax.
|
|
|
Why can't we see past the cosmological horizon?
|
Beyond the cosmological horizon, we are looking back to a time before the universe had formed.
|
|
|
Which of the following types of galaxies are most spherical in shape?
|
ellipticals
|
|
|
Approximately how many stars does a dwarf elliptical galaxy have?
|
less than a billion
|
|
|
Based on counting the number of galaxies in a small patch of the sky and multiplying by the number of such patches needed to cover the entire sky, the total number of galaxies in the observable universe is estimated to be approximately
|
100 billion
|
|
|
Why are Cepheid variables important?
|
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.
|
|
|
How was Edwin Hubble able to use his discovery of a Cepheid in Andromeda to prove that the "spiral nebulae" were actually entire galaxies?
|
From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.
|
|
|
Recall that Hubble's law is written v = H0d, where v is the recession velocity of a galaxy located a distance d away from us, and H0 is Hubble's constant. Suppose H0 = 65 km/s/Mpc. How fast would a galaxy located 500 megaparsecs distant be receding from us?
|
32,500 km/s
|
|
|
Which types of galaxies have a clearly defined spheroidal component?
|
all but irregulars
|
|
|
What do scientists mean by the critical density of the universe?
|
the precise density marking the dividing line between a universe that has enough mass to contract again and a universe that will continue to expand forever
|
|
|
Which of the following types of galaxies are reddest in color?
|
ellipticals
|
|
|
What is the most accurate way to determine the distance to a very distant irregular galaxy?
|
using a white-dwarf supernova as a standard candle
|
|
|
What makes white-dwarf supernovae good standard candles?
|
both A and B
|
|
|
Based on current estimates of the value of Hubble's constant, how old is the universe?
|
between 12 and 16 billion years old
|
|
|
White-dwarf supernovae are good standard candles for distance measurements for all the following reasons except which?
|
White-dwarf supernovae occur only among young and extremely bright stars
|
|
|
What is the Tully-Fisher relation?
|
The faster a spiral galaxy's rotation speed, the more luminous it is.
|
|
|
Suppose that we look at a photograph of many galaxies. Assuming that all galaxies formed at about the same time, which galaxy in the picture is the youngest?
|
the one that is farthest away
|
|
|
Which types of galaxies have a clearly defined disk component?
|
spirals and lenticulars
|
|
|
Which of the following sequences lists the methods for determining distance in the correct order from nearest to farthest?
|
parallax, main-sequence fitting, Cepheid variables, Tully-Fisher relation, Hubble's law
|
|
|
What is the primary practical difficulty that limits the use of Hubble's law for measuring distances?
|
We do not know Hubble's constant very accurately yet
|
|
|
What is the major difference between an elliptical galaxy and a spiral galaxy?
|
An elliptical galaxy lacks a disk component
|
|
|
What two quantities did Edwin Hubble plot against each other to discover the expansion of the Universe?
|
velocity and distance
|
|
|
Hubble's "constant" is constant in
|
space
|
|
|
Which of the following statements about galaxies is true?
|
Small galaxies outnumber large galaxies but large galaxies produce most of the light in the universe.
|
|
|
What is Hubble's law?
|
The recession velocity of a galaxy is directly proportional to its distance from us.
|
|
|
Most large galaxies in the universe are
|
spiral or lenticular
|
|
|
Which of the following types of galaxies are most commonly found in large clusters?
|
ellipticals
|
|
|
Dr. X believes that the Hubble constant is H0 = 55 km/s/Mpc. Dr. Y believes it is H0 = 80 km/s/Mpc. Which statement below automatically follows?
|
Dr. X believes that the universe is older than Dr. Y believes
|
|
|
What is the most accurate way to determine the distance to a nearby star?
|
stellar parallax
|
|
|
Which of the following is true about irregular galaxies?
|
They were more common when the universe was younger.
|
|
|
Dr. Smith believes that the Hubble constant is H0 = 70 km/s/Mpc. Dr. Jones believes it is H0 = 50 km/s/Mpc. Which statement below automatically follows?
|
Dr. Smith believes that the universe is younger than Dr. Jones believes
|
|
|
How does a lenticular galaxy differ from a normal spiral galaxy?
|
It has no spiral arms
|
|
|
How did Edwin Hubble measure the distance to the Andromeda Galaxy?
|
He applied the period-luminosity relation to Cepheid variables
|
|
|
Which of the following is a consequence of Hubble's Law?
|
the more distant a galaxy is from us, the faster it moves away from us
|
|
|
What is a standard candle?
|
an object for which we are likely to know the true luminosity
|
|
|
Elliptical galaxies are more likely to be found in clusters than are spiral galaxies
|
True
|
|
|
Stars are continually forming in the halo of our Galaxy today
|
False
|
|
|
How do we know that there are intergalactic clouds between a distant quasar and us?
|
We see hydrogen absorption lines at redshifts smaller than that of the quasar
|
|
|
What evidence supports the theory that elliptical galaxies come from denser clouds?
|
Elliptical galaxies at high redshifts lack young, blue stars.
|
|
|
Which of the following types of protogalactic clouds is most likely to form an elliptical galaxy?
|
a dense cloud with very little angular momentum
|
|
|
Starburst galaxies produce most of their light in the wavelength range of
|
the infrared.
|
|
|
What evidence supports the idea that a collision between two spiral galaxies might lead to the creation of a single elliptical galaxy?
|
all of the above
|
|
|
Why do we believe that starburst galaxies represent a temporary stage in galaxy evolution?
|
Such galaxies produce so much light that they would have consumed all their gas long ago if they had always been forming stars at this high rate.
|
|
|
Why are telescopes sometimes called "time machines"?
|
because observations of distant objects reveal them as they were in the past
|
|
|
Which of the following is not a piece of evidence supporting the conclusion that active galactic nuclei are powered by accretion disks around massive black holes?
|
Infrared observations show that many stars are forming near the centers of active galaxies.
|
|
|
If an object doubles its luminosity in 10 hours, how large can the emitting source of light be?
|
about 10 light-hours across
|
|
|
What are the typical features seen in quasar absorption lines of intergalactic clouds?
|
The hydrogen line is wider and lines from heavy elements are weaker at higher redshifts.
|
|
|
Which of the following is not a strong argument for the theory that some large elliptical galaxies formed as the result of galaxy collisions?
|
Galaxy collisions are common and most galaxies in the universe are elliptical
|
|
|
The most active galactic nuclei are usually found at large distances from us; relatively few nearby galaxies have active galactic nuclei. What does this imply?
|
Active galactic nuclei tend to become less active as they age.
|
|
|
Which of the following is evidence for supermassive black holes in active galaxies?
|
all of the above
|
|
|
What is a quasar?
|
the extremely bright center of a distant galaxy, thought to be powered by a massive black hole
|
|
|
If we represent the Milky Way Galaxy as the size of a grapefruit (10-cm diameter), the distance to the Andromeda Galaxy would be about
|
3 m.
|
|
|
Where are the X rays produced that are emitted by quasars and other active galactic nuclei?
|
in hot gas in an accretion disk around a central black hole
|
|
|
How is the energy that powers radio galaxies, quasars, and other active galactic nuclei produced?
|
by gravity, which converts potential energy of matter falling toward a central black hole into kinetic energy, which is then converted to thermal energy by collisions among the particles of matter
|
|
|
Which of the following gives the two main assumptions of theoretical models of galaxy evolution?
|
Hydrogen and helium filled all of space, and certain regions of the universe were slightly denser than others.
|
|
|
I observe a galaxy that is 100 million light years away: what do I see?
|
the light from the galaxy as it was 100 million years ago and it is redshifted
|
|
|
Suppose we observe a source of X rays that varies substantially in brightness over a period of a few days. What can we conclude?
|
The X-ray source is no more than a few light-days in diameter.
|
|
|
Which of the following is not true of quasars?
|
Quasars are powered by the intense production of large numbers of stars that can only be sustained for a relatively short time
|
|
|
What is a galactic wind?
|
hot gas erupting into intergalactic space from a large superbubble
|
|
|
Which of the following processes slowed the collapse of protogalactic clouds?
|
the shock waves from the exploding supernovae of the earliest stars
|
|
|
Why is a dense cloud more likely to produce an elliptical galaxy than a spiral galaxy?
|
The higher gas density forms stars more efficiently, so all the gas is converted into stars before a disk can form.
|
|
|
Why should galaxy collisions have been more common in the past than they are today?
|
Galaxies were closer together in the past because the universe was smaller
|
|
|
How many more stars does a starburst galaxy form, in one year, than the Milky Way?
|
about a hundred
|
|
|
What is a central dominant galaxy?
|
a giant elliptical galaxy at the center of a dense cluster
|
|
|
Which of the following cannot be true of the very first stars formed in the Universe?
|
They may have had rocky planets around them.
|
|
|
In the 1960s, Maarten Schmidt determined that quasars were very distant objects by
|
determining their redshifts
|
|
|
What evidence suggests that small galaxies in our Local Group have undergone two or more starbursts in the past?
|
We see small galaxies in which many stars have one age and many others have another age that is billions of years older.
|
|
|
Observations of quasar absorption lines show that intergalactic clouds were more common in the past.
|
True
|
|
|
Galaxies at very large distances from the Milky Way often look distorted.
|
True
|
|
|
Galaxy mergers take hundreds of millions of years to complete.
|
True
|
|
|
A protogalactic cloud with very little angular momentum is more likely to form an elliptical galaxy than a spiral galaxy.
|
True
|
|
|
Galaxy collisions were more common in the past.
|
True
|
|
|
The collision of two spiral galaxies will likely result in a single giant spiral galaxy.
|
False
|
|
|
A protogalactic cloud with slow star formation is more likely to form a spiral galaxy than an elliptical galaxy.
|
True
|
|
|
Some galaxies in the Local Group stopped forming stars for several billion years but then started again
|
True
|
|
|
Quasars radiate most of their energy as radio emission.
|
False
|
|
|
What do peculiar velocities reveal?
|
the distribution of dark matter in large-scale structures
|
|
|
The distribution of the dark matter in a spiral galaxy is
|
approximately spherical and about ten times the size of the galaxy halo
|
|
|
Which of the following are candidates for dark matter?
|
all of the above
|
|
|
Which of the following statements about rich clusters of galaxies (those with thousands of galaxies) is not true?
|
Galaxies in the central regions are predominantly spirals, while elliptical galaxies roam the outskirts.
|
|
|
Some recent but still preliminary measurements of the expansion rate of the universe suggest a problem with our standard idea about how the universe should be expanding. What is the problem?
|
The measurements show that the expansion may actually be accelerating, rather than slowing under the influence of gravity.
|
|
|
Compared to the central regions of spiral galaxies, we expect elliptical galaxies to have
|
higher mass-to-light ratios because stars in elliptical galaxies are dimmer than those in spirals.
|
|
|
What does the universe look like on very large scales?
|
Galaxies appear to be distributed in chains and sheets that surround great voids
|
|
|
Gravitational lensing occurs when
|
massive objects bend light beams that are passing nearby
|
|
|
If there is no dark matter in the Milky Way Galaxy, what is the best alternative explanation for the observations?
|
Our understanding of gravity is not correct for galaxy-size scales.
|
|
|
How do we determine the amount of dark matter in elliptical galaxies?
|
We measure the speeds of stars at different radii from the galactic center and determine how much mass is interior to the orbit.
|
|
|
What do we mean when we say that a particle is a weakly interacting particle?
|
It interacts only through the weak force and the force of gravity.
|
|
|
A large mass-to-light ratio for a galaxy indicates that
|
on average, each solar mass of matter in the galaxy emits less light than our Sun
|
|
|
Which of the following particles are baryons?
|
protons
|
|
|
Why isn't space expanding within systems such as our solar system or the Milky Way?
|
Their gravity is strong enough to hold them together against the expansion of the universe.
|
|
|
Which model of the universe gives the youngest age for its present size?
|
a recollapsing universe
|
|
|
How do we know that there is much more mass in the halo of our galaxy than in the disk?
|
Stars in the outskirts of the Milky Way orbit the galaxy at much higher speeds than we would expect if all the mass were concentrated in the disk.
|
|
|
If a galaxy's overall mass-to-light ratio is 100 solar masses per solar luminosity, and its stars account for only 5 solar masses per solar luminosity, how much of the galaxy's mass must be dark matter?
|
95 percent
|
|
|
What is a typical mass-to-light ratio for the inner region of a spiral galaxy, in units of solar masses per solar luminosity?
|
6
|
|
|
Why do we expect WIMPs to be distributed throughout galactic halos, rather than settled into a disk?
|
Since they do not interact with the electromagnetic force, they do not feel friction or drag and hence do not contract with the rest of the protogalactic cloud.
|
|
|
Why wasn't the intracluster medium in galaxy clusters discovered until the 1960s?
|
The medium emits X rays, which are blocked by the earth's atmosphere and require X-ray satellites in space in order to be observed.
|
|
|
Why do we believe 90 percent of the mass of the Milky Way is in the form of dark matter?
|
The orbital speeds of stars far from the galactic center are surprisingly high, suggesting that these stars are feeling gravitational effects from unseen matter in the halo.
|
|
|
What is the evidence for an accelerating universe?
|
White-dwarf supernovae are slightly dimmer than expected for a coasting universe.
|
|
|
What is meant by "dark energy"?
|
the agent causing the universal expansion to accelerate
|
|
|
How are rotation curves of spiral galaxies determined beyond radii where starlight can be detected?
|
through observations of the 21 cm line of atomic hydrogen
|
|
|
Why do we call dark matter "dark"?
|
It emits no or very little radiation of any wavelength.
|
|
|
How do astronomers create three-dimensional maps of the universe?
|
by using the position on the sky and the redshift to determine a distance along the line of sight
|
|
|
Which of the following is an example of baryonic matter?
|
you
|
|
|
If all the "dark matter" in the Universe were to be, somehow, instantaneously removed, which of the following would not happen?
|
The Solar System would fly apart
|
|
|
Some MACHOs emit radiation. Why are they considered dark matter?
|
They are not as bright as a normal star and are not visible across great distances of space.
|
|
|
What is the ultimate fate of an open universe?
|
All matter decays to a low-density sea of photons and subatomic particles
|
|
|
What fraction of the mass needed to halt expansion is known to exist in the form of visible mass in the universe?
|
less than 1 percent
|
|
|
Why can't the dark matter in galaxies be made of neutrinos?
|
Neutrinos travel at extremely high speeds and can escape a galaxy's gravitational pull.
|
|
|
What evidence suggests that the Milky Way contains dark matter?
|
We observe clouds of atomic hydrogen far from the galactic center orbiting the galaxy at unexpectedly high speeds, higher speeds than they would have if they felt only the gravitational attraction from objects that we can see.
|
|
|
When we see that a spectral line of a galaxy is broadened, that is, spanning a range of wavelengths, we conclude that
|
there are different Doppler shifts among the individual stars in the galaxy
|
|
|
What is Einstein's cosmological constant?
|
a repulsive force that counteracts gravity and was introduced to allow for a static universe
|
|
|
If they exist, MACHOs are expected to be found only in the disk of the Milky Way, whereas WIMPs would be found only in the halo.
|
False
|
|
|
If we learn that the universe is a recollapsing universe, it will mean that the universe is presently contracting, rather than expanding as generally believed.
|
False
|
|
|
Individual galaxies generally have higher mass-to-light ratios than clusters of galaxies.
|
False
|
|
|
Approximately 90 percent of the mass of the Milky Way is located in the halo of the galaxy in the form of dark matter.
|
True
|
|
|
The visible parts of galaxies contribute about one-tenth of the critical density of the universe.
|
False
|
|
|
If the universe is accelerating, it will expand forever.
|
True
|
|
|
By definition, our Sun has a mass-to-light ratio of 1 solar mass per solar luminosity.
|
True
|
|
|
One possible ingredient of dark matter is known as WIMPs, or weakly interacting massive particles. WIMPs probably are made of protons and neutrons.
|
False
|
|
|
The only possible geometry of an accelerating universe is open
|
False
|
|
|
Dark matter is purely hypothetical, because we have no way of detecting its presence.
|
False
|
