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75 Cards in this Set
- Front
- Back
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What happens to stars post main-sequence evolution? |
• After exhausting its hydrogen fuel, a main-sequence star will become a very large, low density star. • More massive stars will fuse the helium in their cores into heavier elements. • The cores of main-sequence stars begin to collapse when they exhaust their hydrogen. • After leaving the main sequence, most stars move to the right on the H-R diagram. |
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How do variable stars provide evidence for sellar evolution?
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• The period of some Cepheid variables actually changes. • Variable stars are expanding and contracting. • A changing period in a Cepheid variable means that the size of the star is changing and that the star is therefore evolving. • Only stars on the instability strip are variable. |
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Why is there a lower mass limit of 0.08 soalr masses for main-sequence stars?
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Object below this mass are not enough to fuse normal hydrogen.
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Why are stars on the instability strip variable? |
Objects above this mass fuse hydrogen too rapidly and cannot stay together. |
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Why does a star's life expectancy depend on mass?
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Mass determines the amount of fuel a star has for fusion and mass determines the rate of fuel consumption for a star.
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Which of the following observable properties of a main-sequence star is a direct indication of the rate at which energy is produced inside that star?
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luminosity
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Why does an expanding giant star become more luminous?
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More energy is produced in the interior, causing the outer layers of gas to expand and increase the surface area of the star.
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When the sun leaves the main sequence to become a giant, what happens to its surface temperature and luminosity?
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The luminosity increases and the surface temperature decreases
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Why will a helium flash never occur in some stars?
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Some stars do not develop degenerate helium cores.
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Why are lower-mass stars unable to ignite more massive nuclear fuels such as carbon?
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They never get hot enough.
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How are the ages of star clusters related to their turnoff points?
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The age of a cluster is the life expectancy of stars at its turnoff point, and the lower the turnoff point, the older the star cluster.
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What is the general trend in the ages of the two types of star clusters?
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Globular clusters are older than open clusters.
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Novae occur in which of the following star systems?
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In binary star systems, when stars are at different stages of evolution
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The accretion disk forms around which star in a binary nova system?
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The white dwarf
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Why do novae occur?
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Matter ignites on the surface of the white dwarf
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What event marks the end of every star's main-sequence life?
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the end of hydrogen fusion in the core
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Why can't the lowest-mass stars become giants?
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They are fully connective and never develop a hydrogen shell fusion zone. |
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What type of spectrum does the gas in a planetary nebula produce?
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an emission line spectrum
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What happens to white dwarfs as they age?
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their surface temperatures decrease and luminosity decreases
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Why have no black dwarfs yet been observed in our galaxy?
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Our galaxy is too young for any to have formed.
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What unusual property do all higher-mass white dwarfs have?
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They are smaller than lower-mass white dwarfs.
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What prevents gravity from shrinking a white dwarf to a smaller size?
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degenerate electrons
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What happens to a star when it becomes a giant if it has a close binary companion?
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Matter can be transferred from the giant to the companion.
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Why can't massive stars generate energy from iron fusion?
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Iron fusion consumes energy. |
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Which type of supernova leaves NO core remnant?
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supernova type Ia
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What are some observed properties of supernovae type Ia and supernovae type II? (hydrogen lines & luminosity) |
Supernovae type II have hydrogen lines in their spectra and supernovae type Ia are more luminous.
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What observational evidence do we have that stellar death black holes really exist?
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Some X-ray binaries have unseen objects with masses greater than 3 solar masses.
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Describe gravitational redshift
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A reduction in the energy of photons as they escape massive objects.
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What prevents neutron stars from contracting to a smaller size?
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Degenerate neutrons.
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Why don't we use visible-wavelength telescopes to locate neutron stars?
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Neutron stars are very hot and small.
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Why does the short length of pulsar pulses eliminate normal stars as possible pulsars?
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An object cannot emit pulses that are shorter than the time it takes light to cross its diameter.
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What is the source of the continuous X-rays emitted by a close binary system that contains a compact object?
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An accretion disk around the compact object is heated by friction.
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What changes would occur if the Sun were replaced with a one solar mass black hole?
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Earth's orbit would not change and the planets would disappear from view. |
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Why some pulsars are not located in supernova remnants?
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Pulsars persist longer than supernova remnants and some pulsars are given high velocities upon formation and can flee the scene of destruction.
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Which of the following is an accurate description of the Schwarzschild Radius?
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It is the radius to which an object must shrink to become a black hole, and it is the radius of the event horizon surrounding a black hole singularity.
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Why do we expect that neutron stars spin rapidly?
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The law of conservation of angular momentum.
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What happens to the protons in the atomic nuclei and the degenerate electrons that were inside the star that creates a neutron star?
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The electrons and protons combine to form neutrons and neutrinos.
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Why are pulsars so hot?
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Gravitational energy was converted into thermal energy during formation.
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How are star clusters distributed in the sky?
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Open clusters lie along the Milky Way, and half of the globular clusters are in or near the constellation Sagittarius.
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What fundamental principle did Harlow Shapley use to calibrate the period-luminosity relationship for Cepheid variable stars?
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Objects with large proper motions tend to be closer than objects with small proper motions.
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Which single wavelength band is best for mapping out the spiral arm structure of the Milky Way galaxy?
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Radio
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What does the observed heavy element abundance tell us about a star?
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A low percentage of metals indicates that a star formed long ago.
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How are population II stars different than the Sun?
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Population II stars have lower metal abundances than the Sun.
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What main conclusion did Harlow Shapley draw from his measurements of the distances to the globular clusters
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The Sun is far from the center of the Milky Way.
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What do we observe at radio, infrared, and X-ray wavelengths near the center of the Milky Way galaxy that leads us to conclude that a supermassive black hole is located there?
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A strong source of radio waves called Sagittarius A*. • A rapid rate of star formation • Supernova remnants |
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What measurements are needed to determine the entire mass of the Milky Way galaxy?
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The rotational velocity of a star near the Galaxy's outer edge and the distance to that star.
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Which of the following are good visible light spiral-arm tracers?
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O and B associations and H II regions.
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What do astronomers think is responsible for the somewhat flocculent, somewhat grand design spiral arms of the Milky Way galaxy?
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Spiral density waves, self-sustaining star formation, and differential rotation.
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At what wavelength band can we observe the center of our Galaxy?
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Radio, Infrared, and X-ray.
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Where are the youngest stars in the Milky Way galaxy located?
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In the flattened disk.
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Why do astronomers propose that the Milky Way galaxy contains a significant amount of dark matter?
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The Galaxy's rotation curve flattens out at great distances.
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If you could view the Milky Way galaxy from a great distance, what colors would you observe for its different components? (Disk/Halo/Nuclear Bulge) (Blue/Yellow)
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The disk is blue, the halo is yellow, and the nuclear bulge is yellow.
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Why does a star's life expectancy depend on mass?
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Mass determines the amount of fuel a star has for fusion and mass determines the rate of fuel consumption for a star.
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Why does an expanding giant star become cooler?
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Energy is absorbed in expanding and lifting the gas of the outer layers.
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Why does an expanding giant star become more luminous?
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More energy is produced in the interior, causing the outer layers of gas to expand and increase the surface area of the star.
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How do star clusters confirm that stars are evolving?
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The H-R diagram of a star cluster is missing the upper part of the main sequence.
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How are the ages of star clusters related to their turnoff points?
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The age of a cluster is the life expectancy of stars at its turnoff point, and the lower the turnoff point, the older the star cluster.
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What can happen to the white dwarf in a close binary system when it accretes matter from the companion giant star?
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The white dwarf can ignite the new matter and flare up as a nova and accrete too much matter and detonate as a supernova type Ia.
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Which of the following statements accurately describe(s) some observed properties of supernovae type Ia and supernovae type II?
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Supernovae type II have hydrogen lines in their spectra and supernovae type Ia are more luminous.
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Why do old supernova remnants emit X-rays?
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The expanding hot gas collides with the interstellar medium. |
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As white dwarfs cool, which of the following occurs? |
They stay the same size and get dimmer.
Why? Degenerate matter cannot contract, and a cooler star is dimmer. |
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Which is the result of the accumulation of mass in a close binary system igniting the core of a white dwarf?
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a nova explosion
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Which is the result of a collapsing iron core in a massive star?
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type II supernova
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Which is the result of mass transfer pushing a white dwarf over the Chandrasekhar limit and its core collapsing, causing all its carbon to fuse at once?
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type Ia supernova
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Which is the result of massive star losing its outer layers in a binary system?
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type Ib supernova
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Galaxies with active star formation also have
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• plenty of gas and dust • O and B associations • Emission nebulae • a bluish tint |
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Which feature of a galaxy seems to be related to the mass of the galaxy's central supermassive black hole?
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The mass of the galaxy's central bulge.
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How does an Sa galaxy differ from an Sc galaxy?
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The Sa galaxy has less gas and dust.
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What parameter must we know to determine the linear diameter and luminosity of a particular galaxy?
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the distance to the galaxy
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What distance indicator are used in extra galactic astronomy?
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• Supernova type Ia • RR Lyrae variable stars • Cepheid variable stars • Brightest globular cluster |
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What observable property of a standard candle must be MEASURED to determine its distance?
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Apparent magnitude
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What gives elliptical galaxies a redder color than spiral galaxies?
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Elliptical galaxies have less gas and dust.
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When viewing a distant galaxy, the amount of look-back time in years is equivalent to the:
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distance to the galaxy divided by the speed of light.
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Why is a supernova type Ia standard candle better to use in measuring very long distances than either the brightest globular cluster or Cepheid variable star standard candles?
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Supernovae type Ia are more luminous.
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What must we know about an object to use it as a distance indicator? |
Either the object's luminosity or the object's linear size.
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