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106 Cards in this Set

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What is the term for the unidentifiable type of mass, that is completely invisible to our eyes, and telescopes, that is the dominant source of gravity in the universe?
Dark matter
What is the "glue" that holds galaxies like our own together?
Gravity of dark matter
Do we know what the Universe is made of?
"We do not know"
What are stars and gas clouds made mostly of?
Hydrogen
Helium
Small amounts of heavier elements mixed in.
T or F
We now believe that the vast majority of the Universe is made of atoms.
False,
We now beleive that the vast majority of the Universe IS NOT made of atoms
T or F
The actual nature of dark matter and dark energy remain completely unknown.
True
What is the term we give to whatever unseen influence is causing the observed gravitational effects we observe?
Dark Matter
T or F
Mounting evidence is suggesting that the expansion of the universe is actually accelerating.
True
What is the term most commonly given to whatever it is that may be causing the expansion of the universe to accelerate?
Dark Energy
List 2 other terms that are interechangeable with the term, "dark energy?"
1. Quintessence
2. Cosmological constant
T or F
More scientists are more comfortable with the idea of dark matter than with dark energy.,
True
What obscures our view of disk stars more than a few thousand light-years away from us?
Interstellar dust
T or F
Radio waves penetrate interstellar dust.
True
T or F
Clouds of atomic hydrogen gas emit a spectral line at the radio wavelength of 21 centimeters.
True
What tells us a cosmic cloud's velocity toward or away from us?
Doppler shift of the 21-cdentimeter line.
What is the term for the model used to summarize the results of orbital velocity measurements which plots the orbital speed of objects against their orbital distance?
Rotation curve
T or F
The inner planets of our solar system orbit at faster speeds than outer planets.
True
T or F
The gravitational force holding a planet in its orbit decreases with distance from the Sun?
True
What happens to the rotation curve in regards to speed with increased distance in our solar system?
It drops-off.
T or F
The rotation curve of any astronomica system whose mass is concentrated toward the center must drop off.
True
T or F
Most of the mass of the Milky Way is not concentrated at its center.
Trure
What happens to the orbits of progressively more distant gas clouds in the Milky Way?
Gas clouds must encircel more and more mass.
What shape of the Milky Way's rotation curve indicates that most of our galaxy's mass lies well beyond our Sun?
The flatness of the Milky Way's rotation curve.
Where is the most of the mass of the Milky WAy located?
In the Sperical halo that surround the disk.
What amount of mass is estimated to be in the spherical halo?
10 X the mass of the disk.
What characteristic of the Spherical halo leads us to believe that the luminous part of the Milky Way's disk is like the tip of the iceberg, marking only the center of a much larger clump of mass?
We have detected very little radiation coming from the spherical halo.
How do we determine the amount of dark matter in a galaxy?
By comparing the galaxy's mass to its luminosity/ or more formally:
mass-to-light ratio?
What do we use a galaxy's mass-to-light ratio to determine?
The amount of dark matter in a galaxy.
What percent of the composition of typical spiral galaxies is dark matter?
90%
What percent of the composition of typical spiral galaxies is matter in the form of stars?
10%
T or F
We can use rotation curves to estimate the amount of dark matter in elliptical galaxies.
False
Why can't we use rotation curves to estimate the amount of dark matter in elliptical galaxies?
The motions of stars in elliptical galaxies are disorganized.
We cannot assemble their velocities into a sensible rotation curve
T or F
Every star in an elliptical galaxy has a slightly different Doppler Shift.
True
What happens to the spectral line for an elliptical galaxy?
Broadens the line spanning a range of wavelengths.
The greater the broadening of a galaxy's spectral line, the ____________ the stars must be moving.
The greater the broadening of a galaxy's spectral line, the FASTER the stars must be moving.
What is the formula for an object's mass-to-light ratio?
TOTAL MASS divided by TOTAL VISIBLE LUMINOSITY:

1Msun/1Lsun
What is the resulting unit of measure for a mass-to-light ratio?
solar mass per solar luminosity
Who discovered dark matter in clusters of galaxies?
Fritz Zwicky
When did Zwicky argue that clusters of galaxies held enormous amount of "mysterious stuff?"
During the 1930s.
T or F
The mass of dark matter in clusters appears to be as much as 50 times the mass in stars.
True
List the 3 ways of measuring cluster masses:
1. measure speeds of galaxies orbiting the center of a cluster;
2. studying the X-ray emision from hot gas between the cluster galaxies;
3. observing how the clusters bend light as gravitational lenses.
What is the term for the hot gas that fills the space between the galaxies in a galaxy cluster?
Intracluster Medium
What is primarily emitted from intracluster medium?
X-raysThe total mass of the cluster.
What does the temperature of intracluster medium depend upon?
The gravitational equilibrium of the gas.
What is the term for massive objects that bend light beams passing nearby?
Gravitational lenses.
What force does all of our understanding of dark matter rest on?
Gravity
What is the name for the category of particles that make up most of the mass of ordinary matter?
Baryons
What is the term for ordinary matter?
Baryonic matter
What is the term for extraordinary matter?
Nonbaryonic matter
What is the term used to describe dark matter?
It is EXTRAORDINARY.
T or F
Matter need not be extraoridnary to be dark.
True
What is the name given to the trillions of faint red stars, brown dwarfs, and Jupiter-size objects left over from theMilky Way's formation that still roam our galaxy's halo, providing much of its mass?
MACHOs
What does MACHOs stand for?
Massive Compact Halo Objects
What is the term given to dim, starlike or planetlke objects?
MACHOs
T or F
MACHOs are too faint for us to see directly.
True
What do we observe that reveals to us that MACHOs exist?
The duration of a lensing event.
What is thought to make up most of the dark matter in the Milky Way, baryonic or nonbaryonic matter?
Nonbaryonic matter
What term is used to describe particles like neutrinos that only interact with other forms of matter through the force of gravity and a force called the weak force?
Weakly interacting particles
Why cannot dark matter in galaxies be made of neutrinos?
1.Because neutrinos travel through the universe at enormous speeds; and
2. Neutrinos can easily escape a galaxy's gravitational pull
What is the term given to the hypothetical particles thought to move more slowly than neutrinos, so that their mutual gravity could hold together a large collection of them?
WIMPs
What does the term WIMPs stand for?
Weakly Interacting Massive Particles
What is the size of the "Massive Particles" in WIMPs?
subatomic particles
Which is thought to be the larger particle, WIMPs or neutrinos?
Neutrinos
What is the other term given to WIMPs?
Cold Dark Matter
What is thought be many astronomers to make up the vast majority of dark matter of all matter in the universe?
WIMPs
T or F
WIMPs can produce photons.
False
WIMPs cannot produce photons.
T or F
Galaxies and clusters of galaxies seem to contain more luminous matter than dark matter.
FALSE
Galaxies and clusters of galaxies seem to contain more DARK MATTER than luminous matter.
What is suspected to have caused the galaxies and clusters to pull together?
Gravitational attraction of dark matter.
Why are stars, galaxies, and clusters of galaxies considered "gravitationally bound systems"?
Because their gravity is strong enough to hold them together.
What has conpletely overwhelmed the expansion?
Gravity
What is preventing our solar system, our galaxy, and our Local Group of galaxies from expanding?
Gravity
What is "peculiar velocity"?
The component of a galaxy's velocity relative to the Milky Way that deviates from the velocity expected by Hubbles' law
What is the term given to large scale clusters that are parts of even bigger gravitationally bound systems that are still in the early stages of formation?
Superclusters
What are seen as groups of clusters that are more immense that clusters of galaxies?
Large-scale structures
In our corner of the universe, how are galaxies arranged?
In huge chains and sheets of galaxies that span millions of light-years
What is the term for the giant empty regions that lie between the chains and sheets of galaxies on astronomical maps?
Voids
What is the name for the recent mapping of our corner of the universe that has measured redshifts for nearly a million galaxies spread across about one fourth of the sky?
Sloan Digital Sky Survey
What is the term for the structure on an astronomical map of our corner of the universe that extends more than 1 billion light-years from end, to end?
Sloan Great Wall, a part of the Sloan Digital Sky Survey
T or F
Hubble established that the galaxies in the universe are rapidly flying towards one another.
False,
Hubble established that the galaxies in the universe are rapidly flying AWAY from one another.
List the 2 general categories that answer what are possible outcomes of the fate of the universe:
1.if gravity is strong enough, expansion will someday halt and the universe will begin collapsing, eventually ending in a cataclysmic crunch; or
2. if the expansion can overcome the pull of gravity, the universe will continue to expand forever, growing ever colder as its galaxies grow ever farther apart.
What is the question re: the universe and its gravity?
Is the universe expanding fast enough to escape its own gravitational pull and keep on expanding forever?
What is the term for the precise density marking the dividing line between eternal expansion and eventual collapse?
critical density
T or F
The universe does NOT appear to contain enough dark matter to prevent it from expanding forever.
True
T or F
Expansion of the universe appears to be speeding up.
True
What is the term for the mysterious repulsive force that is seems to be pushing all the universe's galaxies apart?
Dark energy
List the 4 categories that astronomers consider as the possibilities for the fate of the universe?
1. recollapsing
2. critical
3. coasting
4. accerlerating
What 3 categories of possible fates of the universe assume that gravity is the only force that affectgs the expansion rate of the universe?
1. recollapsing
2. critical
3. coastal
What category of possible fates of the universe ends with a "Big Crunch" when the galaxies will come crashing back, together, and the entire universe ends in a "Big Crunch"?
Recollapsing
What is the category of possible fates of the universe relies on the theory that the universe will never collapse but will expand more and more slowly as time progresses?
Critical
What possible fate of the universe relies on the density of all of the universe equals the critical density?
Critical
What is a "flat universe"?
Mathematically speaking, the overall geometry of the universe is flat, because it stops expanding after infinite time.
What 3 categories of possible fates of the universe assume that there is no dark energy?
1. recollapsing
2. critical
3. coastal
What category of possible fates of the universe relies on the theory that the matter density of the universe is smaller than the critical density, and the collective gravity of all its matter cannot halt the expansion?
Coastal
What category of possible fates of the universe sees the universe as expanding forever, with little change in its rate of expansion?
Coastal
Why is the coastal category so named?
Because the expansion will continue to COAST forever.
What is another name for a coasting universe?
Open universe - because its overall geometry is more like the open surface of a saddle that like the closed surface of a sphere?
What type of universe has the geometrical shape of a saddle?
Open or coastal universe
What category of possible fates of the universe relies on a theory of dark energy exerting a repulsive force that causes the expansion of the universe to accelerate with time, it causes the expansion rate to grow with time?
Accelerating universe
What is another name for a "recollapsing universe"?
Closed universe
Why is a closed universe, or recollapsing universe, so named?
Mathematical calculations show that it must have an overall geometry that closes upon itself like the surface of a sphere, but in more dimiensions.
What is the term given to Einstein's fudge factor?
Cosmological constant
What did Einstein consider to be his "greatest blunder" of his career?
Invention of the cosmological constant
T or F
The idea of a cosmological constant as a valid explanation is gaining ground.,
True
Which type of universe requires the least amount of time to arrive at the current separation between galaxies?
Recollapsing universe
What is the name that is given to the repulsive force that is causing the acceleration in the expansion of the universe?
Dark energy
T or F
Dark energy exists.
WELL< we don't really know.