Astronomy Ch. 21 – Flashcards
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What do X-ray observations tell us about conditions around a potential nova?
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The mass transfer causes an accretion disk to build up around the white dwarf, and as the material spirals in toward the strong gravity of the collapsed star, it is heated up to millions of degrees, hence becoming observable in X-rays. In some cases, this disk is so hot that it outshines the white dwarf, even in visible light. Fluctuations in the transfer create observable short period changes in its light.
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As a star's evolution approaches the Type II supernova, we find
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the heavier the element, the less time it takes to make it. the heavier the element, the higher the temperature to fuse it. helium to carbon fusion takes at least 100 million K to start. the heavier the element, the less time it takes to make it. photodisintegration of iron nuclei begins at 10 billion K to ignite the supernova. Correct: All of the above are correct.
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Which of these is NOT true about supernovae?
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The two types are both closely related to evolution of white dwarfs.
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What is the reason a type-I supernova slows its dimming after about 2 months?
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Energy is released from the decay of radioactive cobalt 56 to iron 56.
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The iron we commonly find in our surroundings came from
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decay of nickel 56 and cobalt 56 in a supernova remnant.
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Nearly all the elements found in nature were formed inside stars, except for
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hydrogen and helium.
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What is stellar nucleosynthesis?
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The formation of heavier elements inside stars.
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The heaviest nuclei of all are formed
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in the core collapse that set the stage of Type II supernovae.
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What made supernova 1987a so useful to study?
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In the Large Magellanic Cloud, we already knew its distance. Its progenitor had been observed previously. We saw direct evidence of nickel to iron decay in its light curve. It occurred after new telescopes, such as Hubble, could observe it very closely. All of the above are correct.
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The making of abundant iron nuclei is typical of
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type II supernovae.
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Which statement about our current knowledge of elements is FALSE?
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We have now produced over 50 radioactive elements not occurring in nature.
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Why does neutron capture work?
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Neutrons have no repulsive barrier to overcome in combining with positively charged nuclei.
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The total energy emitted by the brightest nova explosions is about
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a million Suns.
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At temperatures of ________ K, photons can split apart nuclei until only protons and neutrons are left in photodisintegration.
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ten billion
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What direct evidence do astronomers have that supports the heavy element formation in stars?
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gamma-ray emissions from decay of cobalt 56 in supernovae the presence of technetium in giant star spectra observed elemental abundances light curves of type-I supernovae Correct: All of the above are evidence of this.
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In neutronization of the core, a proton and an electron make a neutron and a
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neutrino
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Why does conversion of its core to iron have to mark the end of a star's life? Which stars can end up with iron cores?
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Stars with a total mass of 8 solar masses may form iron cores. The formation of an iron core ends the normal life of a star because iron cannot be fused into heavier elements and produce energy, as previous fusion reactions have done. In order to fuse iron, energy must be provided. The star, at this point in its evolution, has finally run out of energy sources in its core.
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As seen in 1987, when two silicon 28 nuclei fuse, or when seven alpha particles are added to a Si-28 nucleus, the initial result in either case is
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nickel 56.
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A surface explosion on a white dwarf, caused by falling matter from the atmosphere of its binary companion, creates what kind of object?
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nova
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What can you conclude about a Type I supernova?
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It was originally a low-mass star.
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A 20 solar mass star will stay on the main sequence for 10 million years, yet its iron core can exist for only a
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day
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The Chandrasekhar limit is
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the upper mass limit for a white dwarf.
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For a white dwarf to explode entirely as a Type I supernova, it's mass must be
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1.4 solar masses, the Chandrasekhar Limit.
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Which type of heavy atomic nuclei are most common, and why?
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Even numbered elements, for helium is "giant food" for everything beyond itself.
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Which of these events is not possible?
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white dwarfs and companion stars producing recurrent Type I supernova events
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The supernova that formed M-1, the Crab Nebula, was observed in
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1054 AD by Chinese and other oriental and mid eastern astronomers.
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If it gains sufficient mass, a white dwarf can become a
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type I supernova.
