ASTRONOMY FINAL
Planet searches using the Doppler effect have focused on M stars. Can you think of 3 reasons why?
* M stars have a lower mass so the gravitational tug from a planet on such a low mass star will result in a larger amplitude of its radial velocity curve, making planet detection easier. * M stars' habitable is very close to the star. Since planet search surveys are biased towards detecting planets near their star, a planet detected near a M star is more likely to be in the habitable zone. A planet in the habitable zone is more likely to harbor life, which would be a great thing to discover anywhere else but on Earth. * M mainsequence stars are the dimmest stars possible. If a planet is detected near such a star, the odds of directly detecting the planet are increased since the light of the star would not overwhelm that of the planet as much. * M mainsequence stars are the most common type of stars. It 'd be hard and unrepresentative to study a sample of stars and avoid these common stars.
Which of the following statements is probably true about the very first stars in the universe? A) They were made only from hydrogen and helium. B) They were made from pure energy. C) They were probably orbited only by terrestrial planets, but no jovian planets. D) They were made approximately of 98% hydrogen and helium, and 2% of heavier elements.
A) They were made only from hydrogen and helium.
Why do we think the first generation of stars would be different from stars born today? A) Without heavy elements, the clouds could not reach as low a temperature as today and had to be more massive to collapse. B) Without heavy elements, the nuclear reactions at the center of the stars would be very different. C) Without heavy elements, there was no dust in the clouds and they collapsed faster. D) The Universe was much denser when the first stars were born. E) There were no galaxies when the first stars were born.
A) Without heavy elements, the clouds could not reach as low a temperature as today and had to be more massive to collapse.
The critical density of the universe is the A) average density the universe would need for gravity to someday halt the current expansion if dark energy did not exist. B) actual average density of the universe. C) density of dark matter in the universe. D) density of water. E) density of dark energy in the universe.
A) average density the universe would need for gravity to someday halt the current expansion if dark energy did not exist.
The transit method of planet detection works best for A) big planets in edge-on orbits around small stars. B) big planets in face-on orbits around small stars. C) small planets in edge-on orbits around big stars. D) small planets in face-on orbits around big stars. E) Earth-like planets in any orbit.
A) big planets in edge-on orbits around small stars.
What two quantities did Edwin Hubble plot against each other to discover the expansion of the Universe? A) velocity and distance B) luminosity and distance C) velocity and temperature D) luminosity and temperature E) age and distance
A) velocity and distance
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? A. 32,500 km/s B. 9 km/s C. 65 Mpc/s D. 0.65 times the speed of light E. 65 km/s
A. 32,500 km/s
A planet's density can be measured by combining A. Doppler and transit observations. B. direct imaging from the new generation of space telescopes. C. spectral observations of the planet's atmosphere. D. Doppler and astrometric observations. E. any method that measures the gravitational tug of the planet on the star.
A. Doppler and transit observations.
How does a 1.2solarmass white dwarf compare to a 1.0solarmass white dwarf? A. It has a smaller radius. B. It has a lower surface temperature. C. It is supported by neutron, rather than electron, degeneracy pressure. D. It has a larger radius. E. It has a higher surface temperature.
A. It has a smaller radius.
Which of the following best summarizes what we mean by dark energy? A. It is a name given to whatever is causing the expansion of the universe to accelerate with time. B. It is the energy contained in dark matter. C. It is a type of energy that is associated with the "dark side" of The Force that rules the cosmos. D. It is the energy of black holes.
A. It is a name given to whatever is causing the expansion of the universe to accelerate with time.
Which of the following statements about novae is not true? A. Our Sun will probably undergo at least one nova when it becomes a white dwarf about 5 billion years from now. B. Then a star system undergoes a nova, it brightens considerably, but not as much as a star system undergoing a supernova. C. A star system that undergoes a nova may have another nova sometime in the future. D. A nova involves fusion taking place on the surface of a white dwarf.
A. Our Sun will probably undergo at least one nova when it becomes a white dwarf about 5 billion years from now.
How do we know that halo and bulge stars are older, on average, than disk stars? A. There are no blue halo and bulge stars. B. Halo and bulge stars orbit in random directions but disk stars have more ordered orbits. C. There are no red disk stars. D. We see evidence for new stars forming in the disk today. E. Theories of galaxy formation tell us that the halo and the bulge formed earlier than the disk.
A. There are no blue halo and bulge stars.
Which model of the universe gives the youngest age for its present size? A. a recollapsing universe B. a critical universe C. a coasting universe D. an accelerating universe E. all models give the same age
A. a recollapsing universe
Which of the following types of galaxies are most commonly found in large clusters? A. ellipticals B. spirals C. abnormals D. irregulars
A. ellipticals
The astrometric technique of planet detection works best for A. massive planets around nearby stars. B. planets in edgeon orbits. C. large planets around distant stars. D. large planets around nearby stars. E. massive planets around distant stars.
A. massive planets around nearby stars.
Starburst galaxies produce most of their light in the wavelength range of: A. the infrared. B. the visible. C. X rays. D. all wavelengths. E. the ultraviolet.
A. the infrared.
A planet is detected via the Doppler technique. The velocity change of the star is a measure of: A. the planet's mass and orbital distance. B. the planet's mass and composition. C. the planet's size and density. D. the planet's size and orbital distance. E. the planet's orbital period and eccentricity.
A. the planet's mass and orbital distance.
When we look at a very distant galaxy, billions of light years away, we see it A. when it was younger. B. when it was older. C. Just as it is now. D. when the whole universe was older.
A. when it was younger.
The most active galactic nuclei are usually found at large distances from us. What does this imply? A) Massive black holes existed only when the universe was young and no longer exist today. B) Active galactic nuclei tend to become less active as they age. C) Active galactic nuclei can form only at large distances from the Milky Way. D) The jets seen in many active galactic nuclei must cause them to move far away from us.
B) Active galactic nuclei tend to become less active as they age.
Why are Cepheid variables important? A) Cepheid variables are stars that vary in brightness because they harbor a black hole. B) Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use Cepheids as "standard candles" for distance measurements. C) Cepheids are a type of young galaxy that helps us understand how galaxies form. D) Cepheids are supermassive stars that are on the verge of becoming supernovae and therefore allow us to choose candidates to watch if we hope to observe a supernova in the near future.
B) Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use Cepheids as "standard candles" for distance measurements.
Which of the following gives the two main assumptions of theoretical models of galaxy evolution? A) The beginning of the universe is modeled after a supernova explosion, and all the elements were produced in the proper quantities by the star. B) Hydrogen and helium filled all of space, and certain regions of the universe were slightly denser than others. C) Hydrogen and helium filled all of space, and all the universe was exactly the same density. D) The universe was composed originally only of hydrogen, and all the other elements came
B) Hydrogen and helium filled all of space, and certain regions of the universe were slightly denser than others.
Which of the following statements about the cosmic background radiation is not true? A) It has a temperature of about 3 degrees K above absolute zero. B) It is the result of a mixture of radiation from many independent sources, such as stars and galaxies. C) It had a much higher temperature in the past. D) Its spectrum is close to a perfect blackbody spectrum. E) It appears essentially the same in all directions.
B) It is the result of a mixture of radiation from many independent sources, such as stars and galaxies.
Based on current evidence, how does the actual average density of matter in the universe compare to the critical density? A) If we include dark matter, the actual density equals the critical density. B) The actual density, even with dark matter included, is less than about a third of the critical density. C) The actual density of dark matter and luminous matter combined is no more than about 1% of the critical density. D) The actual density of matter is many times higher than the critical density.
B) The actual density, even with dark matter included, is less than about a third of the critical density.
How do we know that halo stars are older, on average, than disk stars? A) Halo stars orbit in random directions but disk stars have more ordered orbits. B) There are no blue halo stars. C) There are no red disk stars. D) Theories of galaxy formation tell us that the halo formed earlier than the disk. E) We see evidence for new stars forming in the disk today.
B) There are no blue halo stars.
How do we determine the amount of dark matter in elliptical galaxies? A) We measure the orbital velocities of star-forming gas clouds around the outer portions of the galaxy. B) We measure the speeds of stars at different radii from the galactic center and determine how much mass is interior to the orbit. C) We count the number of stars in the galaxy and determine its volume, so that we can calculate the galaxy's density. D) We search for dark lanes of dust and black holes within the galaxy. E) We measure how fast the galaxy rotates as a whole.
B) We measure the speeds of stars at different radii from the galactic center and determine how much mass is interior to the orbit.
How do astronomers create three-dimensional maps of the universe? A) through comparison of computer models of the structure formation with observations B) by using the position on the sky and the redshift to determine a distance along the line of sight C) by using the position on the sky and the galaxy brightness as a measure of distance along the line of sight D) by interpreting the peculiar velocities of each galaxy E) by carefully measuring the parallax of each galaxy
B) by using the position on the sky and the redshift to determine a distance along the line of sight
Which of the following types of galaxies are most commonly found in large clusters? A) spirals B) ellipticals C) lenticulars D) irregulars
B) ellipticals
Why does ongoing star formation lead to a blue-white appearance? A.There aren't any red or yellow stars. B. Bright short-lived blue stars outshine the others. C. Gas in the disk scatters blue light.
B. Bright short-lived blue stars outshine the others.
Why do orbits of bulge stars bob up and down? A. They're stuck to interstellar medium. B. Gravity of disk stars pulls them toward the disk. C. Halo stars knock them back into the disk.
B. Gravity of disk stars pulls them toward the disk.
Why do we believe most of the mass of the Milky Way is in the form of dark matter? A. Theoretical models of galaxy formation suggest that a galaxy cannot form unless it has at least 10 times as much matter as we see in the Milky Way disk, suggesting that the halo is full of dark matter. B. 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. C. Our view of distant galaxies is sometimes obscured by dark blotches in the sky, and we believe these blotches are dark matter located in the halo. D. We observe a lot of Xray gas in our galaxy to can only stay here if there is a lot of mass in the galaxy. E. Although dark matter emits no visible light, it can be seen with radio wavelengths, and such observations confirm that the halo is full of this material.
B. 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 likely to happen if two galaxies collide? A. Their stars will crash into each other. B. Their mutual gravitational pull will greatly distort each galaxy until they merge. C. The galaxies will pass right through each other and continue on a straight path away from one another. D. They will explode.
B. Their mutual gravitational pull will greatly distort each galaxy until they merge.
Which of the following cannot be true of the very first stars formed in the Universe? A. They have all exploded as supernovae by now. B. They had rocky planets around them. C. They have formed singly, in isolation. D. They were very massive. E. They reionized the Universe.
B. They had rocky planets around them.
How do we know that the universe's expansion is speeding up? A. We've measured it for a long time and seen that galaxies are moving faster with time. B. We look at objects from different times in the past to see how expansion changes with time C. We can see the change in the expansion rate from year to year.
B. We look at objects from different times in the past to see how expansion changes with time
What is a standard candle? A. a class of objects in astronomy that all have exactly the same luminosity B. an object for which we are likely to know the true luminosity C. an object for which we can easily measure the apparent brightness D. long, tapered candle that lights easily E. any star for which we know the exact apparent brightness
B. an object for which we are likely to know the true luminosity
Compared to spiral galaxies, elliptical galaxies are A. bluer and rounder. B. bluer and flattened. C. always much smaller. D. redder and flattened. E. redder and rounder.
B. bluer and flattened.
What kinds of objects lie in the halo of our galaxy? A. all of these B. globular clusters C. open clusters D. gas and dust E. O and B stars
B. globular clusters
One can measure the distance between the Sun and the center of the Milky Way by: A. mapping the distribution of gas clouds in the spiral arms. B. mapping the distribution of globular clusters in the galaxy. C. mapping the distribution of stars in the galaxy. D. looking at other nearby spiral galaxies. E. looking at the shape of the "milky band" across the sky.
B. mapping the distribution of globular clusters in the galaxy.
Gravitational lensing occurs when A. massive objects cause more distant objects to appear much larger than they should and we can observe the distant objects with better resolution. B. massive objects bend light beams that are passing nearby. C. dark matter builds up in a particular region of space, leading to a very dense region and an extremely high masstolight ratio. D. telescope lenses are distorted by gravity.
B. massive objects bend light beams that are passing nearby.
What kind of measurement does not tell us the mass of a cluster of galaxies? A. measuring velocities of cluster galaxies B. measuring the total mass of cluster's stars C. measuring the temperature of its hot gas D. measuring distorted images of background galaxies
B. measuring the total mass of cluster's stars
Planets detected via the Doppler technique have been mostly A) Earth-mass, in Earth-like orbits. B) Jupiter-mass, in Jupiter-like orbits. C) Jupiter-mass, in very close orbits. D) Earth-mass, in very close orbits. E) a wide range of masses, in edge-on orbits.
C) Jupiter-mass, in very close orbits.
Recent measurements of the expansion rate of the universe reveal that the expansion rate of the universe is doing something astronomers did not expect. What is that? A) The measurements show that the universe may not be expanding at all. B) The measurements show that the universe may be shrinking rather than expanding. C) The measurements show that the expansion is accelerating, rather than slowing under the influence of gravity. D) The measurements indicate that the universe is at least 30 billion years old, meaning that more than 10 billion years passed between the Big Bang and the formation of the first stars and galaxies. E) The data show that the expansion rate varies widely in different parts of the universe.
C) The measurements show that the expansion is accelerating, rather than slowing under the influence of gravity.
What evidence supports the theory that there is a black hole at the center of our galaxy? A) We observe an extremely bright X-ray source at the center of our galaxy. B) We can see gas falling into an accretion disk and central mass at the center of our galaxy. C) The motions of the gas and stars at the center indicate that it contains a million solar masses within a region only about 1 parsec across. D) We observe a large, dark object that absorbs all light at the center of our galaxy. E) all of the above F) none of the above
C) 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.
If an object doubles its luminosity in 10 hours, how large can the emitting source of light be? A) about 10 light-years across B) about 10 parsecs across C) about 10 light-hours across D) varies depending on how luminous the object is E) varies depending on how far away the object is
C) about 10 light-hours across
Based on current estimates of the value of Hubble's constant, how old is the universe? A) between 4 and 6 billion years old B) between 8 and 12 billion years old C) between 12 and 16 billion years old D) between 16 and 20 billion years old E) between 20 and 40 billion years old
C) between 12 and 16 billion years old
Which of the following methods used to determine the mass of a cluster does not depend on Newton's laws of gravity? A) measuring the orbital velocities of galaxies in a cluster B) measuring the temperature of X-ray gas in the intracluster medium C) measuring the amount of distortion caused by a gravitational lens D) none of the above
C) measuring the amount of distortion caused by a gravitational lens
A large mass-to-light ratio for a galaxy indicates that A) the galaxy is very massive. B) the galaxy is not very massive. C) on average, each solar mass of matter in the galaxy emits less light than our Sun. D) on average, each solar mass of matter in the galaxy emits more light than our Sun. E) most stars in the galaxy are more massive than our Sun.
C) on average, each solar mass of matter in the galaxy emits less light than our Sun.
What is meant by "dark energy"? A) the energy associated with dark matter through E=mc2 B) any unknown force that opposes gravity C) the agent causing the universal expansion to accelerate D the energy of black holes. E) the total energy in the Universe after the Big Bang but before the first stars
C) the agent causing the universal expansion to accelerate
The reason that most extrasolar planets are found close to their parent stars is A) the planets reflect more light the closer they are to the star. B) more of the starlight is blocked by the planet when it transits the star. C) the amount and frequency of the star's motion are both higher. D) the closer to a star, the hotter and therefore brighter the planet is. E) planets that are close to a star are heated up and therefore larger.
C) the amount and frequency of the star's motion are both higher.
What defines the habitable zone around a star? A) the region around a star where rocky planets form B) the region around a star where humans can survive C) the region around a star where liquid water can potentially exist on planetary surfaces D) the region around a star where the ultraviolet radiation does not destroy organisms on a planetary surface E) the region around a star where life exists
C) the region around a star where liquid water can potentially exist on planetary surfaces
Your friend leaves your house. She later calls you on her cell phone, saying that she's been driving at 60 miles an hour directly away from you the whole time and is now 60 miles away. How long has she been gone? A. 1 minute B. 30 minutes C. 60 minutes D. 120 minutes
C. 60 minutes
How does a black hole form from a massive star? A. If enough mass is accreted by a neutron star, it will undergo a supernova explosion and leave behind a blackhole remnant. B. If enough mass is accreted by a whitedwarf star so that it exceeds the 1.4solarmass limit, it will undergo a supernova explosion and leave behind a blackhole remnant. C. 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. D. Any star that is more massive than 8 solar masses will undergo a supernova explosion and leave behind a blackhole remnant. E. A black hole forms when two massive mainsequence stars collide.
C. 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.
True or False?: Starburst galaxies have been forming stars at the same furious pace since the universe was about a billion years old. A. True, starburst galaxies are the most prolific regions of star formation in the universe. B. False, after too many stars form, a black hole results and a galaxy stops forming stars. C. False, the bursts of star formation would use up all the gas in a galaxy in a much shorter period of time than the age of the universe. D. False, starburst galaxies are only found nearby, and are all very young.
C. False, the bursts of star formation would use up all the gas in a galaxy in a much shorter period of time than the age of the universe.
Which of the following statements about rich clusters of galaxies (those with thousands of galaxies) is not true? A. They are sources of Xray emission due to the presence of hot, intergalactic gas. B. The speeds of the galaxies in the cluster indicate that most of the cluster mass is dark matter. C. Galaxies in the central regions are predominantly spirals, while elliptical galaxies roam the outskirts. D. They often have a very large, central dominant galaxy near their center, perhaps formed by the merger of several individual galaxies. E. There likely have been numerous collisions among the member galaxies at some time in the past.
C. Galaxies in the central regions are predominantly spirals, while elliptical galaxies roam the outskirts.
Why do stars in the halo of the galaxy have almost no heavy elements such as carbon, nitrogen, and oxygen? A. Those elements have been used up in halo stars. B. Heavy elements are biological, and there is no life out there to make them. C. Halo stars formed before those elements were made. D. Making C, N, and O requires massive stars, and there are no massive stars in the halo.
C. Halo stars formed before those elements were made.
Why do we call dark matter "dark"? A. We cannot detect the type of radiation that it emits. B. It blocks out the light of stars in a galaxy. C. It emits no or very little radiation of any wavelength. D. It emits no visible light.
C. It emits no or very little radiation of any wavelength.
What is actually happening to the expansion of the universe? A. It is continuing more or less unchanged. B. It is slowing down. C. It is accelerating. D. none of the above
C. It is accelerating.
What would you conclude about a galaxy whose rotational velocity rises steadily with distance beyond the visible part of its disk? A.Its mass is concentrated at the center. B. It rotates like the solar system. C. It's especially rich in dark matter. D. It's just like the Milky Way.
C. It's especially rich in dark matter.
What is the most accurate way to determine the distance to a nearby star? A. mainsequence magnitude B. using Cepheid variables C. Parallax D. using RR Lyrae variables E. Hubble's law
C. Parallax
Why should we not be surprised that galaxy collisions were common in the past? A. Galaxies moved faster in the past and therefore collided more often. B. Galaxies were larger in the past and therefore collided more often. C. The universe was much denser in the past, so its galaxies were much closer together, making collisions much more frequent. D. Because elliptical galaxies are formed by the collision of two spiral galaxies, ellipticals are observed to be more common in the past.
C. The universe was much denser in the past, so its galaxies were much closer together, making collisions much more frequent.
Where are globular clusters located in the Milky Way? A. disk B. central bulge C. halo D. spiral arms
C. halo
What is the effect of dark matter on the formation of galaxies and clusters of galaxies? A.none B. minimal C. key, since it has gravity and is abundant D. unknown, because we don't know the distribution of dark matter
C. key, since it has gravity and is abundant
How do we know that the universe is expanding? A.the big bang theory B.the motion of the Andromeda Galaxy C. the Doppler effect measured in many galaxies D. the first stars
C. the Doppler effect measured in many galaxies
Where are most star-forming regions in the Milky Way? A. the central bulge B. the halo C. the spiral arms D. the regions between the spiral arms E. Star formation happens at roughly the same rate in all regions of the Milky Way.
C. the spiral arms
What does the universe look like on very large scales? A) Galaxies are uniformly distributed. B) Galaxies are randomly distributed. C) Galaxies are distributed in a hierarchy of clusters, superclusters, and hyperclusters. D) Galaxies appear to be distributed in chains and sheets that surround great voids. E) Galaxies are distributed in a great shell expanding outward from the center of the universe.
D) Galaxies appear to be distributed in chains and sheets that surround great voids.
Which of the following is not true of quasars? A) Some quasars are more than a thousand times more luminous than the Milky Way. B) Quasars were more common in the past. C) Quasars are powered by the energy radiated by matter falling into a central black hole. D) Quasars are powered by the intense production of large numbers of stars that can only be sustained for a relatively short time. E) Some quasars can change their brightness every few hours.
D) Quasars are powered by the intense production of large numbers of stars that can only be sustained for a relatively short time.
What happens to the rotation of a gas cloud as it collapses to form a star? A) The rotation rate remains the same and results in stellar rotation. B) The rotation dissipates and any residual is left in small overall rotation of the star. C) The rotation rate increases and results in fast rotation of the star. D) The rotation rate increases and results in a disk of material around a forming star. E) The rotation increases the speed of collapse and produces more massive stars.
D) The rotation rate increases and results in a disk of material around a forming star.
White-dwarf supernovae are good standard candles for distance measurements for all the following reasons except which? A) All white-dwarf supernovae involve the explosion of stars of nearly the same mass. B) White-dwarf supernovae are so bright that they can be detected even in very distant galaxies. C) White-dwarf supernovae are common enough that we detect several every year. D) White-dwarf supernovae occur only among young and extremely bright stars. E) All white-dwarf supernovae have similar light curves, which makes them easy to distinguish from massive-star supernovae.
D) White-dwarf supernovae occur only among young and extremely bright stars.
What is a quasar? A) a starlike object that actually represents a bright patch of gas in the Milky Way B) a very large galaxy thought to be formed by the merger of several smaller galaxies, typically found in the center of a galaxy cluster C) a rotating neutron star whose beam periodically crosses our line of sight D) the extremely bright center of a distant galaxy, thought to be powered by a massive black hole E) another name for very bright stars of spectral type O
D) the extremely bright center of a distant galaxy, thought to be powered by a massive black hole
You observe a galaxy moving away from you at 0.1 light-years per year, and it is now 1.4 billion light-years away from you. How long has it taken to get there? A. 1 million years B. 14 million years C. 10 billion years D. 14 billion years
D. 14 billion years
How does the gravity of an object affect light? A. Visible light coming from a compact massive object, such as a neutron star, will be redshifted, but higher frequencies such as X rays and gamma rays will not be affected. B. Light coming from a compact massive object, such as a neutron star, will be blueshifted. C. Less energetic light will not be able to escape from a compact massive object, such as a neutron star, but more energetic light will be able to. D. Light coming from a compact massive object, such as a neutron star, will be redshifted. E. Light doesn't have mass; therefore, it is not affected by gravity.
D. Light coming from a compact massive object, such as a neutron star, will be redshifted.
What is Hubble's law? A. The redder a galaxy, the older it is. B.The longer the time period between peaks in brightness, the greater the luminosity of the Cepheid variable star. C. The faster a spiral galaxy's rotation speed, the more luminous it is. D. The recession velocity of a galaxy is directly proportional to its distance from us. E. The recession velocity of a galaxy is inversely proportional to its distance from us.
D. The recession velocity of a galaxy is directly proportional to its distance from us.
The transit method of planet detection works best for A. big planets in faceon orbits around small stars. B. small planets in faceon orbits around big stars. C. small planets in edgeon orbits around big stars. D. big planets in edgeon orbits around small stars. E. Earthlike planets in any orbit.
D. big planets in edgeon orbits around small stars.
How is the energy that powers radio galaxies, quasars, and other active galactic nuclei produced? A. by magnetic fields that trap and accelerate charged particles, which then radiate high amounts of energy B. by matterantimatter annihilation near a central black hole C. by matter that has been converted to pure energy being shot out as jets by a central black hole D. 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 E. by nuclear fusion near a central black hole
D. 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
What are the two main differences between extrasolar planetary systems discovered to date and our Solar System? A. extrasolar planet orbits tend to be more eccentric and inclined than in our Solar System B. extrasolar planets tend to be bigger and denser than Jupiter C. extrasolar planet orbits tend to be closer and more circular than in our Solar System D. extrasolar planet orbits tend to be closer and more eccentric than in our Solar System E. extrasolar planets tend to be more massive and dense than Jupiter
D. extrasolar planet orbits tend to be closer and more eccentric than in our Solar System
Which of the following sequences lists the methods for determining distance in the correct order from nearest to farthest? A. mainsequence fitting, parallax, Cepheid variables, Hubble's law B. mainsequence fitting, parallax, Hubble's law, whitedwarf supernovae C. parallax, mainsequence fitting, whitedwarf supernovae, Hubble's law D. parallax, mainsequence fitting, Cepheid variables, Hubble's law E. parallax, mainsequence fitting, Hubble's law, Cepheid variables
D. parallax, mainsequence fitting, Cepheid variables, Hubble's law
The reason that most extrasolar planets are found close to their parent stars is A. the closer to a star, the hotter and therefore brighter the planet is. B. planets that are close to a star are heated up and therefore larger. C. the planets reflect more light the closer they are to the star. D. the amount and frequency of the star's motion are both higher. E. more of the starlight is blocked by the planet when it transits the star.
D. the amount and frequency of the star's motion are both higher.
Which of the following is not evidence for dark matter? A. Xray observations of hot gas in galaxy clusters B. gravitational lensing around galaxy clusters C. the broadening of absorption lines in an elliptical galaxy's spectrum D. the expansion of the universe E. the flat rotation curves of spiral galaxies
D. the expansion of the universe
What did astronomers expect might cause the expansion of the universe to slow down? A. friction B. running out of energy C. being very old D. the gravitational pull of all the matter in it E. none of the above
D. the gravitational pull of all the matter in it
I observe a galaxy that is 100 million lightyears away: what do I see? A. the light from the galaxy as it is today, but it is blueshifted B. the light from the galaxy as it is today, but it is redshifted C. the light from the galaxy as it was 100 million years ago and it it blueshifted D. the light from the galaxy as it was 100 million years ago and it is redshifted E. Nothing: the galaxy lies beyond the cosmological horizon.
D. the light from the galaxy as it was 100 million years ago and it is redshifted
What can you conclude from the fact that quasars usually have very large redshifts? A. They are generally very distant. B. They were more common early in time. C. Galaxy collisions might turn them on. D. Nearby galaxies might hold dead quasars. E. All of the above.
E. All of the above.
What causes the radio pulses of a pulsar? A. The star undergoes periodic explosions of nuclear fusion that generate radio emission. B. The star vibrates. C. A black hole near the star absorbs energy and reemits it as radio waves. D.The star's orbiting companion periodically eclipses the radio waves emitted by the main pulsar. E. As the star spins, beams of radio radiation sweep through space. If one of the beams crosses Earth, we observe a pulse.
E. As the star spins, beams of radio radiation sweep through space. If one of the beams crosses Earth, we observe a pulse.
What kind of star is most likely to become a whitedwarf supernova? A. a binary M star B. an O star C. a pulsar D. a star like our Sun E. a white dwarf star with a red giant binary companion
E. a white dwarf star with a red giant binary companion
What is the basic definition of a black hole? A. a dead star that has faded from view B. any object made from dark matter C. a literal hole through the fabric of spacetime leading to another Universe D. any compact mass that emits no light E. any object from which the escape velocity exceeds the speed of light
E. any object from which the escape velocity exceeds the speed of light
Compared with stars in the disk, orbits of stars in the halo A. do not have to be around the galactic center. B. are relatively uniform to each other. C. do not have to pass through the plane of the galaxy. D. are elliptical but orbiting in the same direction. E. are elliptical, with random orientation.
E. are elliptical, with random orientation.
Which of the following comprise the oldest members of the Milky Way? A. Cepheid variables B. the Sun and other solar mass stars C. O stars D. red giant stars in spiral arms E. globular clusters
E. globular clusters
Compared with our Sun, most stars in the halo are A. old, red, and bright and have fewer heavy elements. B. old, red, and dim and have much more heavy element material. C. young, red, and dim and have fewer heavy elements. D. young, blue, and bright and have much more heavy element material. E. old, red, and dim and have fewer heavy elements.
E. old, red, and dim and have fewer heavy elements.
Helium originates from A. radioactive decay of heavier elements only. B. fusion in stars only. C. fusion in stars with a small contribution from the Big Bang. D. the Big Bang only. E. the Big Bang with a small contribution from fusion in stars.
E. the Big Bang with a small contribution from fusion in stars.
Which planet search technique is currently best suited to finding Earthlike planets? A. gravitational lensing B. astrometric C. Doppler D. combining all of these E. transit
E. transit
The Doppler technique for planet detection has found Earthlike planets around nearby Sunlike stars. TRUE OR FALSE
FALSE
The only possible geometry of an accelerating universe is open. TRUE OR FALSE
FALSE
The visible parts of galaxies contribute about one-tenth of the critical density of the universe. TRUE OR FALSE
FALSE
Briefly explain how Hubble's discovery of a relationship between galactic distance and redshift led to the idea of the Big Bang.
Hubble's discovery means that all galaxies are moving away from each other. That means in the past they were closer to one another, and in the distant past all the matter in the Universe was in a hot dense state.
Rank the following objects from coldest (1) to hottest (5). White dwarf Red Giant Jupiter Neutron Star Sun
Jupiter, Red Giant, Sun, White Dwarf, Neutron star
Draw the Hubble diagram of a decelerating universe.
Making it go left 0,0 to the upper right = decelerating
Rank the following objects from smallest (1) to largest (2). White dwarf Red Giant Jupiter Neutron Star Sun
Neutron Star, White Dwarf, Jupiter, Sun, Red Giant
Could an extraterrestrial astronomer surveying our solar system with the Doppler method discover the existence of Jupiter with a few days of observation? Why or why not?
No, Jupiter's period is really large so it would take years to detect it.
Someone tells you: 'A cluster of galaxies is held together by the mutual gravitational attraction of all the stars in the cluster's galaxies.' What do you tell him/her?
That is false. Most of the mass in a galaxy cluster is in the form of dark matter, which is what is the main source of gravitation holding the cluster together.
Someone tells you 'I'd love to live in one of the galaxies near our cosmological horizon because I want to see the black void into which the Universe is expanding.' What do you tell him/her?
The Universe is not expanding into a void or anything. Spacetime is stretching. If you lived in a galaxy near the Milky Way's cosmological horizon, your horizon would surround you as a perfect sphere with you in the center. The Milky way would be near you cosmological horizon. You'd see galaxies that are past the Milky Way's horizon. Just like when you move on the Earth surface your horizon moves with you and you never see a "drop off" because there is none.
Describe how one would measure the mass within the orbit of the Sun around the center of the Milky Way. If the Milky Way were twice as massive as it is and the distance between the Sun and the center of the Milky Way were inchanged, would the Sun orbit faster, slower, or just the same? If slower or faster, by how much? Explain.
We measure masses of things being orbited by using a modified version of Newton's version of Kepler's 3rd law: M ~ r x v^2 (the mass of thing being orbited is proportional to the distance to the object orbiting it and the velocity squared of the object orbiting). If the mass within the Sun's orbit were twice as large, but r were unchanged, then v^2 would be twice as large so v would be greater by sqrt(2)=1.4. The Sun would be orbit faster.
Briefly describe what happens during the merger of two spirals. Do not forget the intermediate active states.
When two spirals approach each other, they get distorted by tidal effects. Then they merge and produce a starburst since the merging triggers gas clouds in the spiral galaxies to start contracting and form stars. The supermassive black holes of the galaxies merge into an even larger supermassive black hole. This channels gas towards the center of the merged galaxies where the large supermassive black hole lies. An accretion disk forms around the black hole, which turns on an active galactic nuclei, which becomes visible when the starburst period ends. At that point the blue stars created by the starburst die and only red stars are left. We are left with a large spheroidal galaxy, without blue stars nor gas and dust: an elliptical galaxy.
