legible name _________________________________ Astro 203, Section 1, spring 2003, FINAL EXAM Dr Olszewski This is Part One of the final exam. PArt 2 begins at 3pm. Please ensure that your name is on this paper. Circle the letter of the best answer. There are 40 questions. Please ensure that you have a complete exam. This part of the exam is closed book and is from 2pm to 3pm. If you finish early, you may hand it in and go outside till 3pm, when the second half of the exam starts. PLEASE DO SO QUIETLY. There is one best answer for each question. The context of each question is this Astro 203 class. The use of context is a good thing. Course grades will be posted on my door before 11am Monday. They will be posted by last 4 digits of ID, NOT in alphabetical order. Please do not phone/email for grades, I'll get them done sooner if left to do the grading. 1) One of these types of stars actually can be seen to evolve by humans (ie, in one human lifetime or less) a) Massive main sequence star b) Low mass main sequence star c) Red giant d) Supernova 2) There is a way to make elements called the R-Process. In what sort of stars does the R-Process operate? a) Main Sequence stars? b) Red Giants c) Supernovae d) White dwarfs e) Pulsars 3) What would be the analogy to the ``Chandrasekhar limit'' for neutron stars (as opposed to the real Chandrasekhar limit for white dwarfs)? a) the mass limit at which no fusion happens b) the mass limit at which a neutron star cannot be a pulsar c) the mass limit at which a remnant would become a black hole d) the mass limit at which radiation pressure destroys a main-sequence star 4) Imagine a white dwarf right at the Chandrasekhar limit. Now imagine a neutron star a teeny bit above the Chandrasekhar limit. The white dwarf is made of up protons and neutrons and electrons. The neutron star is made up of neutrons, with few electrons and protons. Where did all of the electrons and protons go? a) Mass loss spewed electrons out into the universe. b) More fusion got rid of the protons c) The electrons were forced into the atomic nuclei where they combined with protons to make more electrons d) The electrons fused together to make helium 5) A black hole gives off no light (ignore the accretion disk). A planet gives off no light (that's not completely true, but it's not bad). So, if you're monitoring the wavelengths of spectral lines in a star that's orbiting one of these two objects at a distance of 5AU, how do you tell whether the regular star is orbiting a black hole or a planet? a) It must be a planet. If the star is orbiting a black hole it would get sucked into the black hole and destroyed. b) It must be a black hole. We can't find extrasolar planets. c) A star orbiting a black hole at a distance of 5AU will be orbiting much more quickly than a star orbiting a planet at a distance of 5AU. d) We simply cannot tell the difference. 6) We don't see pulsars in the center of all supernova remnants. Why not? a) Not all pulsars have their beams pointing at Earth. b) Not all supernovae leave behind compact remnants. c) Some supernovae leave behind white dwarfs. d) Some of those ``supernova remnants'' are really star-forming regions. e) a and b 7) We see spectra of a star-forming region, a planetary nebula, and a supernova remnant. These spectra are similar in many ways. How can you tell which spectrum is of the supernova? a) The supernova spectrum will be brighter. b) A supernova will have pulsarium lines superposed. c) A planetary nebula is always perfectly round. d) A supernova remnant has no object at the center. e) We see light from gas moving at very high velocity in the spectrum of the Supernova. 8) If you're inside an ``elevator'', can you tell if you're sitting quietly on the surface of the Earth, or if you're in space being accelerated ``upwards''? a) yes b) no 9) As you get closer and closer to the event horizon of a black hole, you... a) Notice no change because the event horizon is not a physical surface. b) Notice (at least while you're still alive) that you're being stretched from head to toe, and compressed perpendicular to that. c) Notice that not all of the clocks in your rocketship are keeping the same time. d) Discover that you are travelling backwards in time. e) notice that you're emitting vast amounts of Hawking radiation. 10) If the Sun were magically replaced by a 1-solar-mass black hole, what would happen to the Earth's orbit? a) The Earth would spiral into the black hole and disappear. b) The orbit would change because a black hole is not the same size as a star. c) The orbit would not change because we are still being tugged on by a 1-solar-mass object 93 million miles away. d) the orbit would change because black holes tug harder on other matter than do stars. 11) What's the easiest way to find a black hole, a neutron star (not a pulsar), or a white dwarf? a) Look with your naked eye. They're all bright. b) Look at the catalog of nearest stars. There are no faraway black holes, neutron stars, or white dwarfs. c) Look at variable x-ray sources. They are possibly black holes or neutron stars or white dwarfs in orbit about normal main sequence stars or red giants. d) Look at empty places in the night sky. 12) Why don't we notice, in everyday life, that General Relativity is needed to describe nature? a) Newton's Laws work just fine except when gravity is very strong. b) We use General Relativity all the time. We just call it by a different name. c) General Relativity only applies in freely falling elevators. d) General Relativity has to do with atoms. We can't see atoms. 13) Imagine light from a distant star passing very close to the surface of the Sun. According to General Relativity AND to observation, what happens to this light? a) It travels in a straight line just like all light. b) It follows a curved path when it's near the Sun. c) It vanishes because of the Schwarzschild radius of the Sun. d) It becomes blue shifted. 14) What object lights up a planetary nebula? a) external stars b) neutron star ``core'' of the original star c) white dwarf ``core'' of the original star d) fusion of the hydrogen in the planetary nebula. 15) We asked you to read Jocelyn Bell's recollections. What did she say about NOT getting a Nobel Prize for the discovery of pulsars while her dissertation advisor did? a) She said that she had the prize stolen from her. b) She said that she didn't think that students should get Nobel Prizes except under the most special circumstances. c) She said that someday, when someone actually does get a Nobel Prize for pulsars, that she was sure she'd get one. d) She said that since pulsars were white dwarfs, she'd discovered nothing especially new. e) She said that the Nobel Prize Committee couldn't track her down because she changed her last name when she got married. 16) Why is a neutron star so much smaller than a white dwarf? a) It weighs less than a white dwarf. b) Atomic nuclei are much smaller than atoms. c) The pulsations of the pulsar make it smaller. d) We don't know how big a neutron star is. 17) From where do we ``steal the energy'' of a neutron star to make a pulsar? a) From gravitational collapse. b) From the spin of the neutron star. c) From material falling onto the neutron star. d) From the other star in the binary system. 18) One of the prediction of General Relativity is that gravity bends light. Where have we seen evidence that this actually occurs? a) From changes in the positions of stars near the Sun during an eclipse. b) From multiple images of a few objects in the sky. c) from long luminous arcs in clusters of galaxies. d) all of the above e) none of the above. 19) What sort of object is at the center of the Crab Nebula? a) White dwarf. b) Massive main sequence star. c) Neutron star (pulsar). d) black Hole. e) none of the above 20) If you could squeeze a human small enough to turn the human into a black hole, how small a space would ``150 pounds of human'' need to occupy? a) Smaller than an atom. b) A few inches. c) Half our current size. d) We'd actually have to get bigger. e) You cannot make a black hole out of less than 2-3 solar masses of material. 21) Why does an astronaut falling into a solar-mass black hole get stretched to death? a) Because this is a compact object, the force of gravity on your feet is substantially greater than the force of gravity on your head. b) Because of the speed at which the astronaut falls in. c) Because of the Equivalence Principle. d) Because of the accretion disk. 22) Why does a planetary nebula give off light? a) It's a hot gas. b) It's absorbed photons from the central star and is now re-emitting them. c) From material falling into the white dwarf. d) Because of the accretion disk. 23) What holds a white dwarf up against gravity? a) ``ideal gas'' pressure b) fusion c) electron degeneracy d) neutron degeneracy e) nothing 24) What holds a neutron star up against gravity? a) ``ideal gas'' pressure b) fusion c) electron degeneracy d) neutron degeneracy e) nothing 25) What holds a black hole up against gravity? a) fusion b) electron degeneracy c) neutron degeneracy d) nothing e) event horizon 26) What is our best model for the NOVA (NOT supernova) phenomenon? a) ignition of hydrogen that has fallen onto the surface of a white dwarf b) iron nuclei being turned into manganese nuclei, which in turn are broken into pieces by high energy photons c) a spinning, pulsating object d) ``Nova'' means new star, so the protostar model is the best one 27) Apparently there are two ways to make a supernova. One of them involves the death of a massive star. Which explanation below is our best model? a) iron core collapses, neutron star forms, outer layers of collapsing star bounce off of the neutron star and are ejected at high speed b) ignition of hydrogen that has fallen onto the surface of a white dwarf c) ``too much'' material inside the event horizon d) fusion uses up all of the hydrogen in the star 28) As in question 27, the other way to make a supernova involves an exploding white dwarf. Which explanation below is our best model? a) ignition of hydrogen that has fallen onto the surface of a white dwarf b) ignition of the core of a white dwarf from changes in structure due to hydrogen that has fallen onto the surface of a white dwarf c) a white dwarf turning into a neutron star d) a white dwarf made from a massive star rather than from a low-mass star 29) We claim that a white dwarf can only exist below 1.4 solar masses. So how can a 7 Solar-mass main-sequence star become a white dwarf? a) mass loss in post-main-sequence evolution b) in special cases a white dwarf can exceed the 1.4 solar mass Chandrasekhar limit c) this is simply wrong; 7 solar masses is larger than 1.4 solar masses d) both b and c 30) How do we know that a ``7 Solar-mass main-sequence star [can] become a white dwarf?'' a) as in question 29, we don't know! b) from the luminosity of the main sequence turnoff of young clusters containing white dwarfs c) from the laws of gravity d) from General Relativity 31) Why did the pulsar discoverers at first ``worry'' that they'd found a signal from an extraterrestrial civilization? In other words, what makes a pulsar signal seemingly more like an extraterrestrial signature than a natural signature? a) a pulsar sends out a changing number of pulses every second, say 2,3,5,7,11..., just like a mathematically inclined extraterrestrial civilization might b) a pulsar is brightest in the radio part of the spectrum, just as some scientists have hypothesized a signal from an extraterrestrial civilization might be c) pulsars could be shown to be far away; if the number of extraterrestrial civilization is small, the typical one would be far away d) nothing natural had ever been seen to vary its light output so rapidly and regularly. 32) Why do we expect that a ``newly born'' neutron star will be spinning very rapidly? a) all ``youthful'' traits happen more quickly than old-age traits b) from the conservation of angular momentum c) only a neutron star can spin as fast as a pulsar d) only a rapidly spinning object can become a neutron star 33) Why must the fusion of elements into something more massive than Iron be the end of stellar evolution of a normal star? a) fusing two elements together to make something heavier than Iron takes energy rather than liberates energy b) neutron stars, which this object will become, are made of iron c) iron rusts when exposed to oxygen found in a carbon-oxygen white dwarf d) fusing two elements together to make something heavier than Iron liberates so much energy that the star blows apart 34) Why can't we tell the ``chemical composition'' of a black hole? a) black holes are not undergoing nuclear fusion b) we cannot see ANYTHING inside the Event Horizon c) there was too much mass loss in the process of making a black hole d) the Uncertainty Principle 35) Imagine a 1-Solar-mass main-sequence star, a 1-solar-mass white dwarf, a 1-solar-mass neutron star (suspend disbelief), and a 1 solar-mass black hole. Order these object from the point of view of their ability to make their light output fluctuate (from slowest to fastest). a) white dwarf, black hole, neutron star, main-seq star b) main-seq stat, black hole, neutron star, white dwarf c) black hole, neutron star, white dwarf, main-seq star d) main-seq star, white dwarf, neutron star, black hole 36) What is the current best observation that shows that Gravitational Waves really do exist? How do we hope to directly measure Gravitational Waves in the next 10-20 years? a) existence of Supernovae; LIGO observatory b) existence of Supernovae; Solar-Neutrino Experiment c) orbital changes in ``The Binary Pulsar;'' LIGO observatory d) orbital changes in ``The Binary Pulsar;'' Solar-Neutrino Experiment 37) What is Hawking Radiation? a) a mechanism for a Black Hole to emit some light b) fusion of elements more massive than Iron c) light from radioactive materials given off by a Supernova d) The mechanism that makes a pulsar pulsate 38) How do we use white-dwarf supernovae to determine the size and rate of expansion of the Universe? What new, surprising result comes from observations of white-dwarf supernovae? a) all white-dwarf supernovae have the same luminosity; the Universe is expanding in a different manner than we thought because of ``dark energy'' b) This idea must be incorrect, since we know white dwarfs are intrinsically very faint c) We make an H-R diagram for white dwarfs, just like we did for main-sequence stars; bluer white dwarfs are brighter d) all white-dwarf supernovae have the same apparent brightness; the Universe isn't expanding at all 39) Why don't all supernova remnants have neutron star pulsars in their centers? a) some supernovae apparently made black holes b) not all pulsar beams are pointing at earth c) some supernovae make white dwarfs d) b and c e) and and b 40) How does a massive-star explosion create new elements? a) through rapid nuclear fusion caused by particles travelling at high speeds through the atmosphere of the star b) from the huge numbers of neutrinos created c) from the breakdown of already existing elements d) from the rapid release of gravitational waves