AST 102 Test 3

Ch. 22• Why do all stars spend most of their lives on the main sequence? Fuel for energy production is hydrogen • Which of the following types of stars will spend the longest time (the greatest number of years) on the main sequence? K • Which of the following statements about the main sequence stage in the life of a star is FALSE? Main sequence stars rare in Galaxy • How long a main sequence star remains on the main sequence in the H-R diagram depends most strongly on its mass • Biologists tell us that life on Earth took billions of years to evolve into astronomy students and other examples of intelligent life. If we want to search for planets with intelligent life-forms that evolved over the same period of time that we did, what sorts of stars should we not bother searching around? O and B type stars • The event in the life of a star that begins its expansion into a giant is almost all hydrogen in core that hot enough for fusion been turned into helium • As a star becomes a giant, its outer layers are expanding. Where does the energy for expanding these layers come from? From fusion of hydrogen into helium in a shell around core • 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? Core collapsing under own weight • 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 upper right • 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 time, and want to know which star will become a red supergiant first, which of the following stars should they bet on? Star was type O on main sequence star • A type of star cluster that contains mostly very old stars is globular star cluster • 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? globular cluster • How are globular clusters distributed in our Milky Way Galaxy? Mostly large spherical halo (or cloud) surrounding flat disk of Galaxy • 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 satisfy his extravagant tastes? Globular cluster Omega Centauri • Which of the following statements about open clusters of stars is FALSE? contain more mass than any other type cluster • 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 • If you wanted to discover the youngest stars you could find in some grouping of stars in the Galaxy, which type of star group would be the best to search? Stellar associations • 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? O and B type stars • An astronomy student, for her PhD, really needs to estimate the age of a cluster of stars. Which of the following would be part of the process she would follow? Plot H-R Diagram for stars in cluster • 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? Point on main sequence where star begins to “turn off” • The oldest structures in our Galaxy turn out to be globular clusters • When the core of a star reaches a temperature of about 100 million degrees (K), something new happens in the core. What is this new event? 3 helium nuclei begin fusing Carbon • If you trace back the history of a carbon atom in your little finger through all of cosmic history, where did this atom most likely originate? Fused from 3 helium nuclei in core of red giant star long before Sun existed • After it experiences a "helium flash" a star like the Sun will have a brief period of stability, fusing helium into carbon (and sometimes oxygen). During this brief stable stage, the star NOTA • Why can a star with a mass like our Sun not fuse (produce) further elements beyond carbon and oxygen? Just cannot get hot enough for fusion of heavier nuclei • When stars become giants, which of the following does NOT usually happen? Mass grows significantly as they incorporate planets and interstellar matter near star • Why is it easier for red giants to lose mass than main sequence stars? Red giants so big, gravity at surface is less • Really massive stars differ from stars with masses like the Sun in that they can fuse elements beyond carbon and oxygen in hot central regions • Many names used by astronomers are misleading or outdated. A good example is the term planetary nebula, which astronomers use to refer to: shell let go by dying low mass star • In a planetary nebula, the shell of expelled material is glowing intensely. What is the main source of energy for this glow? Ultraviolet radiation from collapsing hot star at center • If most stars are low-mass stars, and low-mass stars typically eject a planetary nebula, why then do astronomers see relatively few planetary nebulae in the sky? Planetary nebulae expand rapidly • Which of the following stages will our own Sun go through in the future: AOTA • Which of the following statements about the mass of the Sun during its lifetime is correct? Sun lose significant mass before and after red giant phase • 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 made in cores of significantly more massive stars than Sun, • 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? First generation stars contain little to no elements heavier than helium Ch. 23• Which of the following statements about the life of a star with a mass like the Sun is correct? As star is dying • A star with a mass like the Sun which will soon die is observed to be surrounded by a large amount of dust and gas -- all material it has expelled in the late stages of its life. If astronomers want to observe the radiation from such a giant star surrounded by its own debris, which of the following bands of the spectrum would be the best to use to observe it? Infrared • When a single star with a mass equal to the Sun dies, it will become a white dwarf • Which of the following stages will the Sun definitely go through as it gets older? Red giant, white dwarf, black dwarf, source planetary nebula • Which of the following is a characteristic of degenerate matter in a white dwarf star? Electrons get close to each other • A white dwarf, compared to a main sequence star with the same mass, would always be: smaller in diameter • The astrophysicist who first calculated the highest mass that a dying star can have and still be a white dwarf was S. Chandrasekhar • A charming friend of yours who has been reading a little bit about astronomy accompanies you to the campus observatory and asks to see the kind of star that our Sun will ultimately become, long, long after it has turned into a white dwarf. Why is the astronomer on duty going to have a bit of a problem satisfying her request? After white dwarf cools off • 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. If we can show that the white dwarfs are definitely part of the cluster, how can their presence so soon in the life of the cluster be explained? Some stars lose lot of mass • Because white dwarfs are small, as their name implies, they are hard to see. What is a way astronomers have to find white dwarfs that distinguishes them from main sequence stars? White dwarfs get really hot • The most stable (tightly bound) atomic nucleus in the universe is: iron • What incident in a massive star's life sets off (begins) the very quick chain of events that leads to a supernova explosion? Fusion of iron • When the mass of a star's core is greater than 1.4 times the mass of the Sun, degenerate electrons can’t keep it stable as a white dwarf. Instead, it becomes: neutron star • 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 • A neutron star is as dense as nucleus of atom • Which of the following is the smallest? Neutron star Which of the following is the largest (in diameter)? Red giant • After the core of a massive star becomes a neutron star, the rest of the star's material explodes outward as supernova • Which of the following stages can only occur in the life of a low-mass star (whose final mass is less than 1.4 times the mass of the Sun)? white dwarf • Astronomers have long realized that supernovae -- when they explode -- give off an enormous amount of light. But observations of Supernova 1987A (in the Large Magellanic Cloud) revealed that the supernova gives off even more energy in another form? That form is: neutrinos • If observations of supernovae in other galaxies show that such an explosion happens in a spiral galaxy like the Milky Way on average every 25 to 100 years, why have astronomers on Earth not seen a supernova explosion in our Galaxy since 1604? Disk of galaxy • Which of the following is NOT a result of supernova explosions? Neutron star disrupted tears apart many pieces • Your sweetheart gives you a piece of gold jewelry as a present to celebrate your passing your astronomy class. Where did the gold atoms in that gift originally come from (where were they most likely made)? built up • Astronomers believe that the many supernova explosions that happened in the Milky Way Galaxy could have played a role in the evolution of life over billions of years. How would they have influenced the development of life on Earth? Cosmic rays • Elements heavier than iron can be created during: supernova explosion • Which of the following statements about a Type II Supernova is true? Occurs at end of life of star with 10 times mass of Sun • Which of the following statements about Supernova 1987A is FALSE? Exploded relatively close to us • In a supernova like SN1987A, once the crisis of iron fusion has begun, roughly how long does it take the star’s core to collapse? Few tenths of a second • How did Supernova 1987A demonstrate that new elements are made in supernova explosions? Light output kept at high levels • Some of the energy produced in the event we call Supernova 1987A was used to blow the star apart. Out of the following places that the energy of this event could go, which absorbed by far the most energy? Production huge number neutrinos • When neutron stars were first predicted theoretically, no scientist expected to be able to detect one of them across interstellar distances. What enabled astronomers to find neutron stars in the late 1960's? found strongly magnetic neutron star • What kind of telescope did Jocelyn Bell use to discover pulsars in 1968? Radio • Which of the following statements about the Crab Nebula is FALSE? Inside number of new formed massive stars (O and B) • 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? Doppler shift in line radiation of nebula • Astronomer have concluded that pulsars are rotating neutron stars • In the model that astronomers have developed for pulsars, why do they suggest that there must be two beams of energy coming from the pulsar? Neutron star beams • Which of the following is one reason we do not detect a pulsar in many remnants of supernova explosions? Pulsar beam doesn’t point towards us • Where does the energy come from that allows the Crab Nebula to keep shining almost a 1000 years after the star exploded? (Who ultimately "pays the energy bill"?) neutron star slowing down • A member of the college football team wants to weigh as much as possible. Assuming he could somehow survive on all of them, at the surface of which object would he weigh the most? Neutron star • Although centuries ago, astronomers thought that a nova was a new star, appearing for the first time in the heavens, today we know that it is: binary star system • When a star undergoes a nova explosion, it may return to its “quiet state” and later become a nova again. What would allow a nova explosion to happen to a star more than once? Star that goes nova has companion star near • In a Type Ia supernova, the cause of the violent outburst is: transfer of mass from companion star • A type Ia supernova involves the transfer of mass from one star to a companion white dwarf? Yet, in some cases, astronomers cannot locate a star near where they see Type Ia explosions. How do they explain the absence of a companion star? Suggest some type la supernova caused by collision 2 white dwarfs • Astronomers have discovered pulsars spinning 500 x per second or more. How do astronomers think pulsars got to be spinning so outrageously fast? Fast spinning pulsars • How did observations with the Compton Gamma-ray Observatory show that gamma-ray bursts were not coming from the Milky Way Galaxy? Gamma rays came from all over sky • When the BeppoSAX satellite, together with telescopes on the ground, helped astronomers pinpoint the location of the first gamma-ray burst to be identified with something that gave off visible light, the burst’s location turned out to be in distant