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Exam 3 AST
| Question | Answer |
|---|---|
| Really massive stars differ from stars with masses like the Sun in that they | can fuse elements beyond carbon and oxygen in their hot central regions |
| How are globular clusters distributed in our Milky Way Galaxy? | mostly in a large spherical halo (or cloud) surrounding the flat disk of the Galaxy |
| Which of the following statements about open clusters of stars is FALSE? | they typically contain more mass than any other type of cluster |
| As a cluster of stars begins to age, which type of star in the cluster will move off the main sequence of the H-R diagram first? | the O and B type stars |
| If stars with masses like our Sun’s cannot make elements heavier than oxygen, where are heavier elements like silicon produced in the universe? | heavier elements are made in the cores of significantly more massive stars than the Sun, which can get hotter in the middle |
| An eccentric Hollywood movie producer, vacationing in Australia, goes to an observatory and offers to make a big donation if they can show him a place in the Milky Way Galaxy where there are more than a million stars seen together. Which object would | The globular cluster Omega Centauri |
| A group of graduate students, bored during a cloudy night at the observatory, begin to make bets about the time different stars will take to evolve. If they have a cluster of stars which were all born at roughly the same tim | a star that would type O on the main sequence star |
| A science fiction writer needs an environment for her latest story where stars are as crowded together as possible. Which of the following would be a good place to locate her story? | in a globular cluster |
| Which of the following statements about the main sequence stage in the life of a star is FALSE? | main sequence stars are rare in the Galaxy, so we are lucky to be living around one |
| The event in the life of a star that begins its expansion into a giant is | almost all the hydrogen in its core that was hot enough for fusion has been turned into helium |
| In a science fiction television show set in the far future, a starship finds itself approaching a stellar association. What types of objects would they be most likely to notice in such an association as they approach? | bright O and B type stars |
| Why do all stars spend most of their lives on the main sequence? | because the fuel for energy production in this stage of the star's life is hydrogen; and that is an element every star has lots and lots of |
| If we look back to the first generation of stars made when the Galaxy was first forming, how do they differ from stars being formed today? | the first generation stars contain little or no elements heavier than helium |
| Many names used by astronomers are misleading or outdated. A good example is the term planetary nebula, which astronomers use to refer to: | the shell let go by a dying low-mass star |
| Why can a star with a mass like our Sun not fuse (produce) further elements beyond carbon and oxygen? | because they just cannot get hot enough for the fusion of heavier nuclei |
| Why is it easier for red giants to lose mass than main sequence stars? | red giants are so big, the gravity at their surface (that holds material to the star) is less |
| When a star first begins the long path toward becoming a red giant, a layer of hydrogen around the core begins to undergo fusion. If this layer was too cold to do fusion throughout the main sequence stage, why is it suddenly warm enough? | the core is collapsing under its own weight and heating up from the compression; this heats the next layer up |
| When the outer layers of a star like the Sun expand, and it becomes a giant, which way does it move on the H-R diagram? | toward the upper right |
| On an H-R diagram of a cluster of stars, which characteristic of the diagram do astronomers use as a good indicator of the cluster's age? | the point on the main sequence where stars begin to "turn off" -- to move toward the red giant region |
| An astronomy student, for her PhD, really needs to estimate the age of a cluster of stars. Which of the following would be part | plot an H-R diagram for the stars in the cluster |
| the rate at which a star or other object emits electromagnetic energy into space; the total power output of an object | luminosity |
| an object intermediate in size between a planet and a star; the approximate mass range is from about 1/100 of the mass of the Sun up to the lower mass limit for self-sustaining nuclear reactions, which is about 0.075 the mass of the Sun | brown dwarf |
| a sequence of stars on the Hertzsprung–Russell diagram, containing the majority of stars, that runs diagonally from the upper left to the lower right | main sequence |
| a measure of the amount of light received by Earth from a star or other object—that is, how bright an object appears in the sky, as contrasted with its luminosity | apparent brightness |
| difference between the magnitudes of a star or other object measured in light of two different spectral regions—for example, blue minus visual (B–V) magnitudes | color index |
| the angular change per year in the direction of a star as seen from the Sun | proper motion |
| a binary star in which the components are not resolved but whose binary nature is indicated by periodic variations in radial velocity, indicating orbital motion | spectroscopic binary |
| two stars that revolve about each other | binary stars |
| a plot of luminosity against surface temperature (or spectral type) for a group of stars | h-r diagram |
| the classification of stars according to their temperatures using the characteristics of their spectra; the types are O, B, A, F, G, K, and M | spectral class |
| a large, dense, cold interstellar cloud; because of its size and density, this type of cloud can keep ultraviolet radiation from reaching its interior, where molecules are able to form | molecular cloud |
| a unit of distance in astronomy, equal to 3.26 light-years; at this distance, a star has a parallax of 1 arcsecond | parsec |
| the attenuation or absorption of light by dust in the interstellar medium | interstellar extinction |
| a graph that displays the time variation of the light from a variable or eclipsing binary star or, more generally, from any other object whose radiation output changes with time | light curve |
| the color change of starlight passing through interstellar dust because dust scatters blue light more effectively than red | reddening |
| a star that belongs to a class of yellow supergiant pulsating stars; these stars vary periodically in brightness, and the relationship between their periods and luminosities is useful in deriving distances to them | cepheid |
| an apparent displacement of a nearby star that results from the motion of Earth around the Sun | parallax |
| the cycling of mass in and out of the interstellar medium, including accretion of gas from intergalactic space, loss of gas back into intergalactic space, and conversion of interstellar gas into stars | baryon cycle |
| tiny solid grains in interstellar space thought to consist of a core of rocklike material (silicates) or graphite surrounded by a mantle of ices; water, methane, and ammonia are probably the most abundant ices | interstellar dust |
| the gas and dust between the stars in a galaxy | interstellar medium |
| luminous knots of gas in an area of star formation that are set to glow by jets of material from a protostar | H-H object |
| the building up of heavy elements from lighter ones by nuclear fusion | nucleosyntesis |
| large, cold interstellar clouds with diameters of dozens of light-years and typical masses of 100,000 solar masses; found in the spiral arms of galaxies, these clouds are where stars form | giant molecular clouds |
| a shell of gas ejected by and expanding away from an extremely hot low-mass star that is nearing the end of its life (the nebulae glow because of the ultra-violet energy of the central star) | planetary nebula |
| a comparatively loose cluster of stars, containing from a few dozen to a few thousand members, located in the spiral arms or disk of our Galaxy; sometimes referred to as a galactic cluster | open cluster |
| a very young star still in the process of formation, before nuclear fusion begins | protostar |
| a line denoting the main sequence on the H–R diagram for a system of stars that have completed their contraction from interstellar matter and are now deriving all their energy from nuclear reactions, but whose chemical composition has not yet been | sero-age main sequence |
| the outflow of gas, sometimes at speeds as high as hundreds of kilometers per second, from a star | stellar wind |
| one of about 150 large, spherical star clusters (each with hundreds of thousands of stars) that form a spherical halo around the center of our Galaxy | globular cluster |
| a nearly explosive ignition of helium in the triple-alpha process in the dense core of a red giant star | hellium flash |
| a region in spacetime where gravity is so strong that nothing—not even light—can escape | black hole |
| a variable radio source of small physical size that emits very rapid radio pulses in very regular periods that range from fractions of a second to several seconds; | pulsar |
| a disturbance in the curvature of spacetime caused by changes in how matter is distributed; gravitational waves propagate at (or near) the speed of light. | gravitational wave |
| the disk of gas and dust found orbiting newborn stars, as well as compact stellar remnants such as white dwarfs, neutron stars, and black holes when they are in binary systems and are sufficiently close to their binary companions to draw off material | accretion disk |
| a stellar explosion produced at the endpoint of the evolution of stars whose mass exceeds roughly 10 times the mass of the Sun | type II supernova |
| a compact object of extremely high density composed almost entirely of neutrons | neutron star |
| the boundary of the region around a black hole where the curvature of spacetime no longer provides any way out | event horizon |
| the cataclysmic explosion produced in a binary system, temporarily increasing its luminosity by hundreds to thousands of times | nova |
| Einstein’s theory relating gravity and the structure (geometry) of space and time | general theory |
| a gas that resists further compression because no two electrons can be in the same place at the same time doing the same thing (Pauli exclusion principle) | degenerate gas |
| How did observations with the Compton Gamma-ray Observatory show that gamma-ray bursts were not coming from the Milky Way Galaxy? | the gamma-rays came from all over the sky, not just the plane of the Galaxy |
| Which of the following statements about our best candidate for long-duration gamma-ray bursts is FALSE? | it involves the merger of two black holes |
| Which of the following statements about the life of a star with a mass like the Sun is correct? | as the star is dying, a considerable part of its mass will be lost into space |
| Astronomers have noticed that the visible filaments in the Crab Nebula are moving toward us at great speed. How can they know about motions like this? | from the Doppler shift in the line radiation from the nebula |
| Astronomer have concluded that pulsars are | rotating neutron stars |
| In a collapsing star of high mass, when electrons and protons are squeezed together with enormous force, they turn into a neutron and a: | neutrino |
| Which of the following stages will the Sun definitely go through as it gets older? | all the other options |
| A rich donor to your college gets fascinated by gamma-ray bursts, and wants to give money to find out more about what produces them. Which of the following should her money go to fund? | a network of visible-light telescopes which can automatically swing to a location provided by an alert system at NASA |
| Astronomers now have a good idea for explaining how the short-duration gamma-ray bursts might come about. Which of the following is part of their explanation? | these bursts most likely come from the merger of two neutron stars |
| A neutron star is as dense as | the nucleus of an atom |
| When a single star with a mass equal to the Sun dies, it will become a | white dwarf |
| Astronomers observe a young cluster of stars, where stars with three times the mass of the Sun are still on the main sequence of the H-R diagram. Yet the cluster contains two white dwarfs, each with a mass less than 1.4 times the mass of the Sun. | some stars can lose a lot of mass on their way to becoming white dwarfs; thus the white dwarfs could have started out as quite massive stars |
| What is a key reason that gravitational waves are so much harder to detect than electro-magnetic (e-m) waves? | gravitational waves are much weaker than e-m waves, and therefore require very, very precise equipment to detect |
| Einstein suggested that the regular change (advance) in the perihelion of the planet Mercury could be explained by: | a distortion in spacetime caused by the gravity of the Sun |
| Suppose each of the following objects could collapse into a black hole. Each black hole would have a sphere around it that is the limit for escape -- once you are inside this region, you cannot get away. For which object would this region be the larg | an entire galaxy of stars (with about a billion stars in it) |
| The equivalence principle (principle of equivalence) says that | the effects of gravity are equivalent to the effects of acceleration |
| From which of the following will a wave of light show the greatest gravitational redshift: | a white dwarf |
| When scientists say that "black holes have no hair", what do they mean? | that once a black hole forms, very little information can be extracted from it about the material that is now inside |
| Wearing a very accurate watch, you volunteer to go on a mission to a black hole in a spaceship that has powerful rockets. You are able to orbit the black hole and stay a little distance outside of the event horizon. Compared to watches on Earth, | more slowly |
| A handsome, rich, but vain movie star notices that he is starting to age, and consults you as his astronomy expert, to see if you can find an astronomical way to slow down his aging. Putting aside practical considerations (such as the | he should travel to a black hole, and spend some time in orbit just above the event horizon |
| What is the Sun's life cycle? | giant molecular cloud, clump of gas and dust, protostar and nebula, main sequence star, subgiant star, red giant, planetary nebula, white dwarf |
| Final state of the Sun | a carbon-oxygen white dwarf |
| Final state of a star with 20 times mass of sun | a supernova with a neutron star remnant |
| final state of A star with 50 times the mass of the Sun | a supernova with black hole remnant |
| final state of A red dwarf star with 10% the mass of the Sun | a white dwarf made mostly of helium |
| final state of A star with 9 times the mass of the Sun | a white dwarf made of oxygen, neon, and magnesium |
| The scientist who made the first telescopic survey of the Milky Way and discovered that it is composed of a huge number of individual stars was | Galileo Galilei |
| In the future, astronomers believe that the Milky Way Galaxy has additional collisions in store. Which of the following nearby galaxies are eventually going to collide with our own? | more than one of the other options |
| Astronomers making observations in our Galaxy have been able to rule out a number of suggestions for what the dark matter in the Galaxy might be. Which of the following have we NOT been able to rule out (which suggestion is still “in the running”)? | a new kind of subatomic particle |
| An astronomer needs to measure the distance to a globular cluster of stars that is part of the Milky Way Galaxy. What method should she try to use to find the distance? | find a variable star (cepheid or RR Lyrae) in the cluster |
| Which of the following statements about dark matter in the Galaxy is FALSE? | While the dark matter cannot be observed with our present-day instruments, we still have a pretty good idea what it consist of |
| Astronomers observe the Small Magellanic Cloud (SMC), a not very dense, rather small galaxy near us. They notice that even those stars that formed recently have relatively few heavier elements (when compared to such recent stars in our Milky Way.) W | because the SMC is small and its stars are widely spaced, the rate of star formation (and star death) is much slower there |
| What objects did Harlow Shapley use as "signposts" to figure out the extent of the Milky Way Galaxy and the location of its center? | globular clusters |
| William Herschel thought that the Sun and Earth were roughly at the center of the great grouping of stars we call the Milky Way. Today we know this is not the case. What was a key reason that Herschel did not realize our true position in the M | the dust that extends throughout the disk of the Galaxy only allowed Herschel to see the small part of the Milky Way that surrounds us |
| How do astronomers measure the mass that the Galaxy contains inside the orbit of the Sun? | they measure the distance to the center of the Galaxy and the period of the Sun's orbit and then use Kepler's Third Law |
| What have we learned from the work of Harlow Shapley and others about the location of the Sun in the Milky Way Galaxy? | we are in the disk of the Galaxy, about 3/5 of the way from the center |
| You suddenly get an uncontrollable urge to find out more about the other side of the Milky Way Galaxy (the regions beyond the center). Where should you rush off to? | a radio telescope that can observe at 21-cm wavelengths |
| If I want to find a sizeable collection of Population II stars in the Milky Way Galaxy, where would be a good place to look? | in a globular cluster high above the Galaxy's disk |
| The central region of our Galaxy is not as flat as its main disk of stars. Which of the following has roughly the same shape as our central region of stars? | a peanut |
| What leads astronomers to conclude that the proto-galactic cloud (the cloud from which our Galaxy formed) was roughly spherical? | the oldest stars in the Galaxy (Population II stars, globular clusters) form a spherical halo around the Galaxy; they outline the original shape of the cloud that gave the Galaxy birth |
| Your weird cousin, who is really into astronomy, decides that the return address he uses on his letters is incomplete! To his city, state, and country, he begins to add: "North America, Earth, Solar System..." If he now wants to include the name of the | Orion Spur |
| Which of the following is evidence that the formation process of our Galaxy may have included collisions with smaller neighbor galaxies? | the observation of long moving streams of stars that continue to orbit through our Galaxy’s halo |
| Objects orbiting around the center of the Milky Way obey Kepler's 3rd Law. This means that: | a cloud of gas or star that is further from the center will generally take more time to orbit |
| A “galactic year” as defined by astronomers is: | the time it takes the Sun to revolve once around the center of the Milky Way Galaxy |
| Where would you look for the youngest stars in the Milky Way Galaxy? | in the disk |
| Astronomers now think that there is a black hole with more than 4 million times the mass of our Sun at the center of our Galaxy? Roughly how large would the event horizon of such a supermassive black hole be? | about 17 times the size of the Sun |
| Which of the following statements about interstellar matter is FALSE? | if the matter were spread out evenly, it would be about as dense as the Earth's atmosphere |
| Supposing we launched a very fast dart from the Space Shuttle, pointed in some direction away from any planet, so that it could travel beyond the solar system. What would it be most likely to hit first after traveling outward for a while? | an atom of interstellar gas |
| How do fragile structures like acetaldehyde (CH3CHO) molecules survive in the harsh environment of interstellar space? Why are they not destroyed by high-energy radiation from stars? | such molecules are found only in dense clouds that have a lot of dust; the dust keeps the radiation from hot stars from reaching the molecules |
| You are observing a binary star system and obtain a series of spectra of the light from the two stars. In this spectrum, most of the absorption lines shift back and forth as expected from the Doppler Effect. A few lines, however | the lines come from interstellar matter between us and the star, not from the stars themselves |
| Astronomers were at first surprised to find complicated molecules in the interstellar medium. They thought ultra-violet light from stars would break apart such molecules. What protects the molecules we observe from being broken apart? | such molecules form in clouds that contain significant amounts of dust, and the dust in the cloud protects them from ultra-violet rays |
| What happens in the process of fluorescence? | atoms absorb ultraviolet rays and convert them to visible light as their electrons cascade to lower energy levels |
| An astronomer wants to observe a cloud of cold neutral (not ionized) hydrogen, far away from any stars. What would be an instrument that could help in this task? | a radio telescope, tuned to a wavelength of about 21 centimeters |
| The red color we see on a lot of photographs of nebulae comes from which element? | hydrogen |
| Why can astronomers not tell from what direction a particular cosmic ray started toward the Earth? | cosmic rays are charged particles and are thus spiral around the Earth and the Galaxy's magnetic field |
| The dust in the dust clouds in interstellar space consists of | tiny solid grains |
| A friend of yours who has not taken an astronomy class looks at your textbook and really likes the picture of the Pleiades, a cluster of stars surrounded by a bluish reflection nebula. She wants to know what causes that beautiful blue glow. | the blue color of the Earth's sky |
| Which of the following is NOT a way astronomers discover clouds of interstellar matter that have a large amount of dust in them? | by giving off x-rays from hot gas surrounding the dust cloud |
| The light element lithium (which, on Earth, is part of medications that improve the lives of people with mental health illnesses) is more common in cosmic rays than it is in the Sun and the stars. What do astronomers think is the reason for this? | because cosmic rays move so fast, they can collide with atoms of carbon, nitrogen, and oxygen and break them apart, producing more light elements like lithium |
| Among interstellar clouds, the hotter the cloud, the | the lower the density of particles in it |
| Where is the outer rim of the Local Bubble located today? | about 200 light-years from the Sun, in the rough direction of the constellations of Orion, Perseus, and Auriga |
| If an astronomer wants to find and identify as many stars as possible in a star cluster that has recently formed near the surface of a giant molecular cloud (such as the Trapezium cluster in the Orion Nebula), what instrument would be best for | an infra-red telescope (and camera) |
| If you want to find stars that are just being born, where are the best places to search? | in giant molecular clouds |
| The Orion Nebula is | a large cloud of gas and dust illuminated by the light of newly formed stars within it |
| A Herbig-Haro (HH) object is | where a jet from a star in the process of being born collides with (and lights up) a nearby cloud of interstellar matter |
| Astronomers identify the "birth" of a real star (as opposed to the activities of a protostar) with what activity in the star? | when nuclear fusion reactions begin inside its core |
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