AST 115: FINAL EXAM
121 Cards in this Set
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Black Holes
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Mass causes this, near sun; 1919 Solar Eclipse data was consistent with the General Theory of Relativity
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formation of a black hole
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when a supernova explodes, the core is squeezed to an intense density, which distorts the fabric of space-time
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event horizon
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mathematical surface at which escape velocity equals the speed of light
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singularity
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mathematical point which the imploded core of a massive star is reduced unless some force exists to support it
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What happens to the material after the supernova core collapses into a black hole?
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we have no way of knowing what becomes of it
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How many solar masses from the core are required to form a black hole?
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three solar masses
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How can you detect a black hole?
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it must be in the presence of other matter to detect it; black holes can be detected in close binary systems
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How can we detect a black hole in a binary system?
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we measure the x-rays from those systems; an example is Cygnus X-1
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How are supermassive black holes detected?
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once a black hole forms, it can accumulate additional mass and grow
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Where are supermassive black holes located?
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in the center of galaxies, which help explain the orbital motion of stars, increasing the event horizon
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What are the 3 measurable characteristics of a black hole?
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total mass inside the black hole, net electric charge of the black hole, and the spin rate of the black hole
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Why do black holes spin?
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it is due to conservation of annular momentum
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Milky Way
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the irregular band of faint white light that encircles the entire inside of the celestial sphere
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How do galaxies congregate in the Universe?
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they form in clusters and superclusters
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How many galaxies are in a cluster?
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100s to 1000s which extend 10-20 MLY across
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How many galaxies can superclusters have?
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10,000s which are 150-300 MLY in size
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poor cluster
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has less galaxies than average
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rich cluster
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has more galaxies than average
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What is the closest rich cluster?
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Virgo Cluster, which has over 1,000 members
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voids
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the mostly empty pockets of the universe which are typically 150 MLY across
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isotropic
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the same in all directions
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homogenous
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uniform in space
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What two words would describe the distribution of galaxies in the Universe?
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isotropic and homogenous
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Why do galaxies collide and stars do not?
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Separation between galaxies is 10s of times their diameter; separation between stars is 10,000,000s of times their diameter
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What is released when galaxies collide?
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heated gas and xrays
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starburst galaxies
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created when compressed gas from colliding galaxies form
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How was Dark Matter discovered?
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by studying orbital motion of various objects in the Galaxy
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What is the Galactic Rotation Curve?
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a plot of the magnitude of the orbital velocities (i.e., the speeds) of visible stars or gas in that galaxy versus their radial distance from that galaxy's center, typically rendered graphically as a scatter plot
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What percentage of the Galaxy may be Dark Matter?
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90%
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What does WIMPS stand for?
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weakly interacting massive particles
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What does MACHOS stand for?
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massive compact halo objects
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What are Elliptical (E) galaxies?
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range circular (E0) to elongated (E7) little to no dust/no now current star forms
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What are Normal Spirals (S)?
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range large nucleus, tightly wound arms (Sa) through small nuclear with loosely wound arms (SC)
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What are Barred Spiral galaxies (SB)?
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range from (SBa through SBc as in a normal spiral) BUT arms emerge from a bar of stars through the nucleus
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What are irregular galaxies (Irr)?
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Show no symmetry; contain both gas and dust, young and old stars
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What are Flocculent Spiral Galaxies?
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"fleecy" chaotic poorly defined arms; domino effect on star formation
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What is a Grand Design Spiral?
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has symmetrical and well defined arms; rotation triggers arm forms (Ex. M81)
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What causes the spiral arms?
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they are formed naturally in a rotating disk with dense waves
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What classification scheme did Hubble use to identify different galaxies?
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the tuning fork diagram
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Which galaxies tend to be smaller and dimmer with fewer stars?
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irregular galaxies
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Which galaxy is the largest in size?
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elliptical galaxies
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How do galaxies tend to congregate?
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they congregate in clusters and superclusters
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How many galaxies do clusters contain?
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100's to 1,000's of members 10 - 20 MLY across
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How many galaxies do superclusters contain?
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10,000's of galaxies in them and are 150 - 300 MLY across
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What is a rich cluster?
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one which has more than the average number of galaxies
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What is a poor cluster?
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one which has less than the average number of galaxies
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What is the nearest rich cluster of galaxies?
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Virgo Cluster
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What are voids, in relation to galaxies?
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sponge-like pocket material which surround superclusters
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What two words are used to describe the distribution of the galaxies in the Universe?
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isotropic and homogenous
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What does isotropic mean?
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the same in all directions
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What does homogeneous mean?
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uniform in space
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Do both galaxies and stars collide?
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No; stars do not collide but galaxies do
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Why do galaxies collide but stars do not?
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the separation between galaxies in 10's of times their diameter; separation between stars is 10,000,000's of times their diameter
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How are Giant Ellipticals formed?
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they form by mergers in cannibalism
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What does the term "mergers" mean?
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during this process, roughly two equal galaxies combine or "merge"
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What does the term "cannibalism" mean?
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during the process of colliding galaxies, the larger galaxy devours a smaller one (Ex. M87)
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In our galaxy, what does a flat galactic curve imply?
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there is a presence of Dark Matter
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How much of the universe is estimated to be made up of Dark Matter?
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23%
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What is the main method of measuring in space?
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Parallax
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What are three alternative methods to measuring in space?
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surveying/triangulation, variable stars, novas and supernovas
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What is the "standard lightbulb" technique?
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measuring the apparent magnitude of an object, then measuring or estimating the absolute magnitude of that object
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How old is the universe?
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14 billion years old
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What has the greatest distance in measurement?
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Supernovas
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Which galaxies showed greater redshift?
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the dimmer and presumably more distant galaxies
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What is the "Hubble Law"?
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the farther away a galaxy is, the greater its recessional velocity is
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What is the greatest "meter stick" used in measuring distance?
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the Hubble Law
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What is the "look back" principle?
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the farther you look into space, the earlier back in time you see
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How much of a delay is the light of the Sun as we see it on Earth?
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8 minutes
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What are "quasars"?
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quasi-stellar radio sources; they are hyperactive centers of very distant, young galaxies
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What do quasars do?
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they contain hot gas
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What are quasars constantly doing?
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moving away from us rapidly
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What are active galaxies?
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those that have bright nuclei associated with great energy production or energetic outflows of matter; AGN (active galaxy nuclei)
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What are double lobed (radio) galaxies?
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two regions of strong radio emission occur on either side of a "peculiar" galaxy
EX. Cyngus A
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What does the term "peculiar" mean?
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it does not fit in with the Hubble classification scheme
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What are jet galaxies?
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a stream of material from the center of a galaxy
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What do jet galaxies emit?
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radiowaves, light, and other wavelengths like xrays
EX. M87
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What is another name for an active galaxy?
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radio galaxy
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What percentage of quasars emit strong radio waves?
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10%
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How would one describe the brightness of a quasi-stellar object (QSO)?
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very luminous
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What is a Quasi-Stellar Object?
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another name of a quasar which emits strong radio waves
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What is the power source of quasars?
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supermassive black holes
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What is the model for explaining various kinds of active galaxies and quasars?
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if we one of the jets nearly face on, it is perceived as a quasar; if we see the jets at other angles, we perceive active galaxies with a jet, or else double-lobed radio emission
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How do quasars qualify to be used to test Einstein's General Relativity Theory?
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How do quasars qualify to be used to test Einstein's General Relativity Theory?
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How does spacetime bend?
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it should be curved in the vicinity of dense concentrations of matter
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What three aspects of Einstein's theory have been detected in space?
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rings, crosses, and arcs
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What is cosmology?
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the study of the origin, structure, and evolution of the universe
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What is included in the universe?
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stars, comets, planets, gas, galaxies, dust, etc... and space
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Olbers' Paradox
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asks the question of how the night sky can be dark if the universe is infinite and full of stars
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What was the surprising implication of Hubble's result?
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the universe is continually expanding
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Since space is expanding, do galaxies also get larger?
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no; space itself is expanding, carrying clusters and superclusters of galaxies away with it; the galaxies themselves don't get larger
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How many astronomers have come to the conclusion that there is not a center of the universe?
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all observers of the universe
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What is the fact about galaxies in the universe which all astronomers have come to the same conclusion?
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there is no center of the universe
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What are the six implications of an expanding universe?
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1) no center 2) no edge 3) expansion rate is slowed by gravity 4) the expansion rate is increased by "dark energy" 5) #4 is greater than #3 so the universe is accelerating 6) the universe began with the BB theory
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How do we know that the Big Bang Theory has accurately predicted that the universe is changnig?
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the number of quasars per unit volume increases, then drops out
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Are there any quasars locally now?
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there are none here locally because they've all moved away; there were many years ago
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What does CMB stand for?
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Comic (Microwave) Background Radiation
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Who discovered CMBs?
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Penzias and Wilson
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How is the CMB strong evidence for the Big Bang Theory?
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through peering out of the microwave telescope and observing how far back in time we are seeing, we can see that the universe cooled to about 3,000 degrees K at the age 380,000 years and became transparent photons for the first time
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What did Penzias and Wilson observe in regards to the CMB and redshifting?
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they detected that if radiation comes from great distance, it will be redshifted into infrared and radio microwave wavelengths
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What does COBE stand for?
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cosmic background explorer
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Which satellite in 1990 measured the CMB more precisely and showed a perfect fit to theory?
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the Cosmic Background Explorer (COBE)
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What did the WMAP (Wilkinson Microwave Anisotropy Probe) indicate?
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the age of the universe is 13.8 billion years old
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What is the cosmological principle?
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the universe must look the same to any observe for all time
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What is the steady-state theory?
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the universe has always existed and will always exist; disproven by the Big Bang Theory
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What is the string theory?
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the belief that the ultimate framework of the Universe may consist of vibrating one-dimensional units known as "strings." This predicts the existence of an additional seven space dimensions and time for a total of eleven
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Who was Fred Hoyle?
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the man who came up with the "Big Bang Theory" name, a strong advocaate of the steady-state theory
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What is the progression of the Big Bang Theory?
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1) Big Bang initiated expansion 2) Plank Time in which only radiation existed 3) rapid expansion 4) protons, quarks, electrons, radiation 5) T low enough for fusion, H and He made 5) Universe became transparent to radiation 6) galaxies formed 7) now
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What is the best explanation of the phenomenon in the Universe?
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the Big Bang theory is the best explanation of how our universe formed
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What three things were merged as one single force under extreme conditions in the early Universe?
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nuclear forces, electromagnetism, and gravity
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What are Grand-Unified Theories (GUTs)?
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descriptions of how scientists have been trying to find ways to unify the forces
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What has been added to the BB to explain the uniformity of the CMB and the "cosmic horizon" problem?
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inflation
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What does uniformity mean?
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isotropy and homogeneity
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What is the cosmic horizon problem?
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It points out that different regions of the universe have not "contacted" each other because of the great distances between them, but nevertheless they have the same temperature and other physical properties. This should not be possible, given that the transfer of information (or energy, …
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What is a closed universe theory?
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the universe stops expanding after a finite time, then a contracting occurs
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What is a flat universe theory?
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the universe coasts to a halt after infinite time; a unique version of BB
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What is an open universe theory?
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universe is still expanding after infinite time; things get dark and cold everywhere
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What is interstellar dust and what is it not?
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it is not dark matter and it is not a radiation, but it has gravity invisible at all wavelengths
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What is the nickname of M81 in Ursa Major?
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nicknamed "Swirl"
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What sort of galaxies do regular clusters contain?
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(mainly) ellipticals
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What do quasars look like in photos?
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star-like objects
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What does the term "static" mean in terms of astronomy?
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A change in illumination
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AST 115: Chapter 2