Final Exam 2
Current observations suggest that the density of all matter and the density of dark energy are
a) (upside down horseshoe) m = 0.3 and (upside down horseshoe) ^ = 0.7, respectively.
If a galaxy has an apparent velocity of 700 km/s, what is its distance if the Hubble constant is assumed to be 70 km/s/Mpc?
a) 10 Mpc
Two galaxies are currently separated by 55 Mpc. Roughly how long did it take for them to reach this separation?
a) 13.7 billion years
Roughly what percentage of the total mass of a galaxy is made up of luminous, or normal, matter?
a) 5-10 percent
What is the escape velocity from the surface of a 1 MSUN AGB star that has a radius of 100 RSUN?
a) 60 km/s
What did Edwin Hubble study in the Andromeda Galaxy that proved it was an individual galaxy and not part of our own Milky Way?
a) Cepheid stars
By comparing globular clusters, you find that Cluster A's RR Lyrae stars are 100 times fainter than Cluster B's RR Lyrae stars. You know that both clusters have approximately the same chemical composition and age, and thus their RR Lyrae stars should have the same luminosities. Which is true about the clusters' distances?
a) Cluster A is 10 times farther away than Cluster B.
What is the reason for the very fast rotation of neutron stars?
a) It is a consequence of the conservation of angular momentum applied to collapsing objects.
Our galaxy is part of the _________ Supercluster.
a) Laniakea
How do we know that at least one generation of stars formed and died before the Milky Way's globular clusters formed?
a) The stars of the oldest globular cluster have some heavy elements.
The accelerated expansion of the Universe was observationally discovered using
a) Type Ia supernovae.
What is the meaning of the phrase inertial frame of reference?
a) a reference frame that is not accelerating
Earth's motion results in the apparent phenomenon of
a) aberration of starlight.
As a protostar evolves towards becoming a main-sequence star, its core temperature will
a) always increase.
What type of spectrum do most stars produce?
a) an absorption spectrum on top of a blackbody spectrum
The chemical element that forms the "backbone" of DNA molecules is
a) carbon.
The interstellar medium is divided into three different kinds of gas clouds. These are
a) cold gas at 100 K, warm gas at 8000 K, and hot gas at about 1 million K.
parallax is used to measure a stars
a) distance.
Dark matter is most likely made up of
a) elementary particles that have mass but do not interact much with normal matter.
When solar activity is very high, the Earth's atmosphere will
a) expand.
The spectra of most galaxies tell us that
a) galaxies appear to be moving away from us.
The expansion of the universe will eventually render the CMB invisible because its photons will
a) have wavelengths that will exceed the size of the observable universe.
The absolute magnitude of a star is a measure of its
a) luminosity.
The ability of a celestial body to retain an atmosphere would depend mainly on which of the following properties?
a) mass and size
What are two ways that Type la supernovae can be produced?
a) mass transfer and stellar mergers
Which of the following are the only observable properties of black holes?
a) mass, angular momentum, and electrical charge
One general property of living organisms is that they
a) modify their environment.
More luminous giant galaxies tend to have __________ supermassive black holes at their centers.
a) more-massive
The existence of the cosmic background radiation tells us that the early universe was
a) much hotter than it is today.
If you were to fall to within the event horizon of a black hole, you would
a) never be able to escape.
A grand unified theory (GUT) unities which forces?
a) only electromagnetism, weak nuclear forces, and strong nuclear forces
Hereditary essentially implies the ability to
a) pass on a genetic code to the next generation.
The Crab Nebula is an important test of our ideas about supernova explosions because
a) people saw the supernova and later astronomers found a pulsar inside the nebula.
Hubble's constant, H0, represents the
a) rate of expansion of the universe.
The detection of solar neutrinos confirms that
a) the Sun's core is powered by proton-proton fusion.
The energy released during the process of nuclear fusion comes from
a) the change in nuclear binding energy.
What is the Planck era?
a) the earliest moments after the Big Bang.
Helium burns in the core of a horizontal branch star via the ________ and produces ________.
a) triple-alpha reaction; carbon
Dark matter is essential in understanding the formation of the large-scale structure in the universe in that it
a) was clumpier than normal matter in the early universe.
When is the Sun most luminous?
a) when there are a maximum number of sunspots
a type la supernova occurs when a white dwarf exceeds a mass of
b) 1.4 MSUN•
What is the approximate temperature at the center of a Sun?
b) 1.5 x 10^7 K
You measure the redshift of a distant galaxy and find, using Hubble's law and assuming a Hubble constant of 70 km/s Mpc, that it's distance is 1 billion ly (310 Mpc.) Imagine that an observer in that galaxy is measuring the recession speed of the Milky Way at the same time as your measurement. What would be the speed that the remote alien observer would record?
b) 21,700 km/s
If a star's measured parallax is 0.2 arcsec, what is its distance?
b) 5 pc
what relationship exists between a star's distance and its parallax?
b) Distance is inversely proportional to parallax.
What is the major difference between prokaryotes and eukaryotes?
b) Eukaryotes have a nuclear membrane surrounding their DNA, and prokaryotes do not.
The James Webb Space Telescope is designed to observe the most distant galaxies in the universe. It will observe them in
b) IR wavelengths.
The best hypothesis about the nature of dark matter is that it consist of particles with no electric charge. What is one reason why dark matter particles must have zero electric charge?
b) If they did, they would emit photons as they move in external magnetic fields.
What caused early astronomers to believe that our galaxy is only about 6,000 light-years across?
b) Interstellar dust blocked visible light from stars farther away.
Why can Type Ia supernovae be used to determine a galaxy's distance?
b) Most Type Ia supernovae have approximately the same peak luminosity.
Star A and star B appear equally bright in the sky. Star A is twice as far away from us as star B. Which of the following is true?
b) Star A is four times as luminous as star B
Star A is a red star. Star B is a blue star. Which star is hotter?
b) Star B is hotter.
Which of the following is evidence that the object known as Sagittarius A* is a supermassive black hole?
b) Star orbits imply a large, invisible mass.
As a subgiant star becomes a red giant, its luminosity increases while its temperature remains approximately constant. What does this mean?
b) The radius is increasing.
Why is 21-cm radiation one of the best ways to map the spiral arms of the Milky Way?
b) These photons, which are produced by neutral hydrogen, are not blocked by the dense clouds of gas and dust in the disk.
How did the presence of cyanobacteria on Earth in the past enable the layer appearance of more advanced life-forms, such as humans?
b) They initiated the oxygenation of the atmosphere.
What happens to active galaxies when their AGNz run out of fuel?
b) They simply become normal galaxies.
The Milky Way appears as _________ in the night sky because _________.
b) a faint band of light sprinkled with dark clouds; the Sun lies in the disk
AGNs are most likely powered by
b) accreting supermassive black holes.
The equivalence principle says that
b) being stationary in a gravitational field is the same as being in an accelerated reference frame.
A red giant star is found to be orbiting an unseen object with a short orbital period. By measuring the speed at which it orbits, astronomers deduce that the unseen object has a mass of 10 MSUN•. This object is probably a __________ because ________.
b) black hole; its mass is too large to be a neutron star or a white dwarf.
In the CNO cycle, carbon is used as a catalyst for the fusion of hydrogen into helium. This means that
b) carbon facilitates the reaction but is not consumed in it.
Active star formation does not typically occur in elliptical galaxies because they
b) contain little cold gas.
In a sunspot, the umbra is
b) cooler than the penumbra.
Structure in our universe evolved by initially forming
b) dwarf galaxies that layer merged to form bigger galaxies.
We can identify only a fraction of all the radio pulsars that exist in our galaxy because
b) few swing their beam of synchrotron emission in our direction.
The most abundant elements manufactured by stars through nuclear reactions are
b) helium, carbon, nitrogen, and oxygen.
A protostar's evolutionary "track" in the H-R diagram traces
b) how the protostar's luminosity, temperature, and radius change with time.
The Milky Way and Andromeda are on a collision course. When will the initial collision happen?
b) in about 4 billion years
According to Hubble's law, as the distance of a galaxy _________, its __________ increases.
b) increases; recessional velocity
During the main-sequence evolution of a massive star, progressively more massive elements are fused in the core until the core is filled with
b) iron.
When the core of a massive star collapses, a neutron star forms because:
b) protons and electrons combine to make neutrons.
Which of the following occurred approximately 500 million years ago?
b) the Cambrian explosion
The most distant globular clusters are found in which part of the galaxy?
b) the halo
The luminosity of a Cepheid star varies in time because
b) the outer envelope of the star contracts and expands radially
The surface of the Sun appears sharp when we look at it in visible light because
b) the photosphere is thin compared with the other layers in the Sun.
What does "habitable zone around a star" mean in the current framework of the search for exoplanets?
b) the region around the star where planetary temperatures would not be too hot or too cold for liquid water to exist
Compared to an electron, the antiparticle of an electron has
b) the same mass but opposite charge.
One phenomenon that can slow star formation in a molecular cloud is
b) the strength of its magnetic field.
One consequence of Einstein's ideas about the speed of light is that
b) whether events are seen as simultaneous or not depends on the motions of observers.
If a stats distance is 10 pc, what is its parallax?
c) 0.1 arcsec
You see a galaxy in which the Hox line (rest wavelength = 656.3 nm) is observed at a wavelength of 756.3 nm. What would be the observed wavelength of a particular helium line that has a rest wavelength of 1,083 nm?
c) 1,248 nm
If a galaxy has an apparent velocity of 700 km/s, what is its distance if the Hubble constant is assumed to be 70 km/s/Mpc?
c) 10 Mpc
We observe neutral hydrogen gas using
c) 21-cm emission.
The largest low-mass stars have masses that are approximately
c) 3 MSun•
The diameter of the Local Group of galaxies is closest to which of the following distances?
c) 3 million parsecs
How many arc seconds are there in 1 degree?
c) 3,600
The Sun will become a red giant star in about
c) 5 billion years.
The bright star named Rigel has a luminosity of 66,000 LSun and a temperature of 11,000 K. What is its radius? Note that the temperature of the Sun is 5,800 K.
c) 70 RSun
At approximately what fraction of the Earth's current age did the first plants on land appear?
c) 90%
Which spectral type has the strongest hydrogen absorption lines?
c) A
What is the difference between apparent brightness and luminosity?
c) Apparent brightness is how much light we see from a star; luminosity is how much light it emits.
You observe three different star clusters and find that the main-sequence turnoff stars in Cluster 1 have spectral type F, the main-sequence turnoff stars in Cluster 2 have spectral type A, and the main-sequence turnoff stars in Cluster 3 have spectral type G. Which star cluster is the youngest and which one is the oldest?
c) Cluster 2 is the youngest and Cluster 3 is the oldest.
What do astronomers mean when they say that the universe is homogeneous?
c) Galaxies are generally distributed similarly throughout the universe.
You observe two stars in a visual binary system using a blue filter that is centered at a wavelength of 550 nm and a red filter that is centered at a wavelength of 650 nm. Star A has a temperature of 10,000 K, while star B has a temperature of 4000 K, and you know that both stars are the same size. Which star will be brighter in each filter?
c) Star A is brighter in both filters.
What is planetary nebula?
c) The ejected envelope of a giant star surrounding the remnant of a star
What should be true about the oldest stars in the Milky Way?
c) They would have few heavy elements because there was not much chance for earlier generations of stars to explode as supernovae before these stars were formed.
Radio waves with 21-cm wavelengths are important because they
c) allow us to study neutral hydrogen in the interstellar medium.
A neutron star in a mass-transfer binary system is called
c) an X-ray binary.
Elliptical galaxies appear red because they
c) contain mostly old stars.
If the material in the universe was at the critical density, expansion would
c) continually slow, but never quite stop.
String theory is
c) currently untestable.
The Big Rip could occur in a universe where the effect of _________ increases with time.
c) dark energy
The Sun's internal magnetic field becomes tangled over time because of
c) differential rotation.
A parsec is a measure of
c) distance.
The luminosity of a Type II supernova _______ with time.
c) first increases, then decreases
When looking at the space between stars, what might you see?
c) gas
Which of these is the correct order of collections of galaxies, from smallest to largest?
c) group, cluster, supercluster
Globular clusters, when compared with open clusters, generally
c) have lower fractions of heavy elements.
Which of the following fills the space between galaxies in a cluster?
c) hot gas that flows at X-ray wavelengths
A 1-MSUN red giant star's energy comes from
c) hydrogen burning to helium in a shell surrounding its core.
Stars are made mostly of
c) hydrogen.
Asymptomatic giant branch stars have ________ luminosities, ________ radii, and _________ escape velocities.
c) large; large; small
In the interstellar medium, molecules survive in regions with
c) lots of dust.
When a spectral-type G2 star like the Sun leaves the main sequence, its
c) luminosity increases and its surface temperature decreases.
To be a standard candle, an object must have a known
c) luminosity.
The "waste" product in the process of photosynthesis is
c) oxygen.
Hydrostatic equilibrium is a balance between
c) pressure and gravity.
The solar magnetic field
c) switches polarity every 11 years.
What characteristic of a star cluster is used to determine its age?
c) the color of the main-sequence turnoff in the cluster
Cosmological redshift is due to
c) the expansion of the space that light travels through.
The disks of spiral galaxies appear blue because
c) they contain active regions of star formation.
We know the Sun's corona is very hot because
c) we observe absorption from highly ionized atoms of iron and calcium in its spectrum.
If there were no dark energy in the universe, the value of __________ alone would determine the evolution and fate of the universe.
d) (upside down horseshoe) m
Neutron stars have masses that range from
d) 1.4 MSUN to 2 MSUN•
If you observe a maximum number of sunspots right now, how long would you have to wait to see the next solar maximum?
d) 11 years
To measure the most accurate parallax possible from Earth's surface, we would make two measurements of a star's position on the sky separated by
d) 6 months
The universe was 10 percent its current size when light left objects observed now at redshift z=
d) 9.
Suppose that scientists in the future are able to observe a star orbiting the central region of the Andromeda Galaxy and fine that it has an orbital period of 31 years and a semimajor axis of 4,500 AU. The mass of Andromeda's central black hole must then be around
d) 9.5 x 10^7 MSUN
In a closed (spherical) universe, the sum of the angles in a triangle is:
d) >180 degrees.
These three barred spirals are the largest members of the Local Group:
d) Andromeda, Milky Way, Triangulum
_______ keeps the core of a red giant star from collapsing.
d) Degenerate pressure from electrons
As a main-sequence star burns its core supply of hydrogen, what happens?
d) Helium builds up in the core.
Which of the following is true about the Great Attractor?
d) It is at the center of the Laniakea Supercluster.
What is the meaning of the word spacetime?
d) It is the combined treatment of space and time in the theory of relativity.
All distant galaxies appear to be moving away from us. Does this mean we are in a special place, and why?
d) No, because all observers will see the same phenomenon.
What critical event transforms a protostar into a normal main-sequence star?
d) Nuclear fusion begins in the core.
Which sequence correctly lists the spectral classes of stars in order from the hottest to coolest?
d) O B A F G K M
Star A and star B both have the same temperature, but different sizes and distances. Star A is more luminous than star B, but star B appears brighter than star A in our sky. Which of these statements about the absolute and apparent magnitudes of the two stars is correct?
d) Star B has a larger apparent magnitude, while star A has a larger absolute magnitude.
What do astronomers mean when they say that the Sun makes energy by hydrogen burning?
d) The Sun is fusing hydrogen into helium and releasing energy.
What is expected to happen to our Solar System when the Andromeda and Milky Way galaxies collide?
d) The Sun may be thrown to a different orbit within the merged galaxies, but the solar system will be relatively uncharged.
As a low-mass main-sequence star runs out of fuel in its core, it grows more luminous. How is this possible?
d) The core shrinks, bringing more hydrogen fuel into the fusing region.
Which of the following Solar System objects is LEAST likely to have, or have had, life?
d) Venus
Star A is a red star. Star B is a blue star. You are able to determine that both stars are the same size. Which star appears brighter is your sky?
d) We also need to know the distance of the stars to determine their brightness
The "Big Crunch" scenario applies to a universe with
d) a density greater than the critical density.
Imagine that you built a time machine and successfully traveled 2 billion years back in time. What would you observe, given our current understanding of Earth's history?
d) a severe scarcity of oxygen in the atmosphere
The gamma-ray bubbles at the poles of our galaxy are evidence that the nucleus of the Milky Way was once a(n)
d) active galactic nucleus (AGN).
Natural selection essentially implies the ability to
d) adapt to environmental changes.
In 1952, chemists Harold Urey and Stanley Miller mixed ammonia, methane, and hydrogen in a closed container, zapped it with electrical sparks, and found that
d) amino acids had been created.
Astronomers know they've found evidence of a past Type II supernova when they find
d) an expanding cloud of hot gas surrounding a neutron star.
The Milky Way Galaxy is a(n) ________ galaxy.
d) barred spiral
The hottest layer of the solar atmosphere is the
d) corona.
The effect of matter on the universe is to
d) decelerate expansion.
The most common type of galaxy found in a galaxy cluster is a _________ galaxy.
d) dwarf
Where in the universe did the Big Bang take place?
d) everywhere in the universe
Spiral arms are generated by
d) gravitational disturbances to a galaxy's disk.
During which phase of the evolution of a low-mass star does it have two separate regions of nuclear burning occurring in its interior?
d) horizontal branch
The red emission (bright region at the top) in the figure shown below is due to
d) ionized hydrogen (H II region).
What particles are the carriers of the electromagnetic force?
d) photons
In the early 1960s, physicists Penzias and Wilson detected a persistent noise at a wavelength of about 1 mm in their radio telescope that came from all directions in the sky due to
d) photons left over from the Big Bang.
Dust reddens starlight because it
d) preferentially affects light at visible and shorter wavelengths.
To verify whether some grand unified theories are correct, physicists are searching for
d) protons that decay.
Massive stars explode when they
d) run out of useful nuclear fuel in their core, and the cores collapse.
The unified model of AGN suggests that quasars, Seyfert galaxies, and radio galaxies are
d) similar phenomena but viewed from different orientation angles.
Sunspots appear dark because they have ____ than those of the surrounding gases.
d) temperatures that are lower
The dominant merchandise by which high-mass stars generate energy on the main sequence is called
d) the CNO cycle.
What provides us the best clues as to the age of a galaxy like ours?
d) the H-R diagrams of globular clusters of stars
Which of the following have both been predicted and conclusively confirmed experimentally?
d) the Higgs boson
That "the physical laws and the properties of the universe are the same everywhere and in all directions" is a statement of
d) the cosmological principle.
The oldest photons we detect in the universe one from
d) the epoch of recombination.
What is ripping apart the Sagittarius dwarf spheroidal galaxy?
d) the gravitational tidal force of the Milky Way
The Andromeda Galaxy is
d) the largest member of the Local Group.
The event horizon of a black hole is defined as
d) the radius at which the escape speed from the black hole equals the speed of light.
Stars evolve primarily because
d) they use up the fuel in their cores.
Even if a black hole emitted no light, we can still detect it
d) through its gravitational effect on surrounding gas or stars.
The Sun eventually will become a
d) white dwarf.
The star named Capella has an apparent magnitude of 0, while the star named Polaris has an apparent magnitude of 2. This means that Capella appears ______ in our sky then Polaris.
e) 6 times brighter
Which of the following is an example of an extremophile?
e) All of these are examples of extremophiles.
What spectral class is the Sun?
e) G2
What does gravity mean in relativity?
e) It is the result of the distortion in spacetime around an object with any energy density.
In which of the following locations has life been found on Earth?
e) Life has been found in all of these locations.
What makes molecules organic?
e) They do again carbon.
Can more than one planet be found in the same habitable zone around a single star?
e) Yes, and this has been observed.
Molecular cloud cores are places where you might find
e) all of these
The evolution of terrestrial life involves which of the following?
e) all of these
Which of the following provides direct evidence for the existence of dark matter?
e) all of these
If one star appears brighter than another in the night sky, then the brighter star
e) cannot be compared to a dimmer star without more information.
An iron core cannot support a massive main-sequence star because iron
e) cannot generate energy when fusing heavier nuclei.
Astronomers use galactic redshift as a measure of
e) distance.
A feature unique to main-sequence stars is that
e) hydrogen burning occurs in their cores.
Which of these fusion reactions begins first in the core of a massive star?
e) hydrogen fusion to helium
Studying standard candles in globular clusters offered the first conclusive proof that our galaxy was much __________ than originally believed.
e) larger
Molecular clouds, which have temperatures of around 10 K, are best observed at ______ wavelengths.
e) radio
Even with infinitely powerful telescopes, we can look back in time only until the time when
e) recombination happened.
Astronomers estimate distances to large numbers of distant galaxies using
e) redshifts.
Sagittarius A*, the radio source located at the center of our galaxy, is believed to be a
e) supermassive black hole.
The spectral class of a star is related to its
e) temperature.
In the Great Debate of 1920, Curtis and Shapley argued over whether or not
e) the spiral nebulae were located outside the Milky Way.
What was the goal of the Urey-Miller experiment schematized in the figure below?
e) to simulate the formation of the building blocks of life
Type la and Type II supernovae are respectively caused by what types of stats?
e) white dwarfs; massive stars