Astrophysics Questions And Answers

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Outline the likely evolution of the star Khad after it leaves the main sequence
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Since it has a mass greater than 1.3 Ms, it will go through a super red giant, onto a supernova to a neutron star or black hole.
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Red supergiant star:
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• Large luminosity • Red color • Relatively low surface temperature • Large mass • Large surface area
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Constellation:
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Group of stars that form a recognizable pattern (as viewed from earth).
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Distinguish between apparent magnitude and absolute magnitude:
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Apparent magnitude is brightness of a star as it appears from earth. Absolute magnitude is the apparent magnitude of a star at a distance from 10Pc.
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State the name of the method that is used to measure the distance of Antares from Earth.
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Stellar/spectroscopic parallax
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Define apparent brightness:
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The power received per unit area at the surface of earth/observer.
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Explain in terms of the Chandrasekhar limit, why its unlikely that Alnitak will develop into a white dwarf:
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The mass limit for a star to become a white dwarf is 1.4Ms, while alnitak’s mass range is between16Ms to 40Ms.
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State the probable final evolutionary state of Alnitak:
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Since it is a high mass star, it will become a neutron star or a black star.
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State Hubble’s law.
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The recessional speed of a galaxy is directly proportional to the distance from earth.
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State why Hubble’s cannot be used to determine the distance from Earth to nearby galaxies, such as Andromeda.
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Local velocity of Andromeda relative to earth is greater than recessional speed due to minimal expansion.
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Outline how CMB is consistent with the Big Bang theory
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Radiation in the universe corresponded to the very high temperature of the BB. As the universe expanded it cooled down and the wavelength of the radiation increased.
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Stellar cluster:
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Stars that are gravitationally bound (close to each other)
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Some stars, such as Betelgeuse are in combination with a companion star forming a spectroscopic binary system. Describe and explain the characters of a spectroscopic binary system
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Spectral lines regularly split into two lines and then recombine. As one star approaches observer the other recedes leading to Doppler shifts in opposite directions.
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Outline with reference to the Oppenheimer-Volkoff limit, the evolutionary steps and the fate of star X after it leaves the main sequence.
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Supernova explosion leaving behind core, core becomes black hole or neutron star. If limit exceeds, star becomes blackhole. If limit is below, star becomes neutron star.
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The density of the universe will determine its ultimate fate. Outline the problems associated with determining the density of the universe:
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Measurement of mass in a given volume is ver uncertain. There is dark matter that is difficult to observe. Measurement of distance is uncertain Matter is not uniformly distributed
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Outline how the expansion of the universe ultimately made it possible for stable nuclei and atoms to exist:
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As universe expands it cools down allowing nuclei in atoms to from.
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Chandrasekhar limit:
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If 12% of the hydrogen of a star is consumed, the star begins expanding.
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Oppenheimer-Volkoff limit:
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If the core is greater than 3 Sm the star becomes a blackhole.
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Suggest how your answers in (a) can be used to predict the fate of a main sequence star.
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In a supernova phase the mass blown leaves a mass less than Chandrasekhar limit; the star evolves into a white dwarf. If mass is greater than 1.4Ms, but less than O-V limit it evolves into neutron star.
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Light from Vega is absorbed by a dust cloud between Vega and Earth. Suggest the effect, if any, this will have on determining the distance of Vega from Earth.
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Vega appears dimmer, hence distance is over-estimated.
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Describe how a large cloud of hydrogen gas can lead to conditions that initiate a fusion reaction.
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Gas cloud contracts by gravity. Gravitational potential energy changes to kinetic energy of particles. Eventually temperature and pressure at center will be so great that fusion starts occurring.
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State the property of a main sequence star that determines for how long hydrogen in its core fuses into helium.
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Its initial mass
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State the end product of nuclear fusion processes in the core of a red giant
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Carbon/oxygen/neon
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State the end product of nuclear fusion processes in the largest red super giants
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Iron
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Suggest one reason why there is uncertainty in the value of the Hubble constant.
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Difficulty in determining galactic distances. Hubble time is constantly increasing.
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Outline the measurements that must be taken in order to determine a value for the Hubble constant.
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Red shift used to measure recessional speed of galaxies. Hubble constant is the gradient of speed-distance graph.

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