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105 terms

Astronomy Exam #4

What is currently the best way to estimate the age of the universe?
Hubble's Constant
What is the current best estimate of the age of the universe?
14 billion years old
If the universe is homogeneous and isotropic, Hubbles Law implies
Universal Expansion
What kind of universe would collapse on itself
Closed Universe
What kind of universe represents the critical point were the universe never collapses on itself
Flat Universe
what kind of properties do irregular galaxies have?
typically smaller than spiral galaxies, exhibit vigorous star-forming activity, some show evidence for prior collision or close encounter with another galaxy.
What is true about galaxies that are measured from earth with high speeds?
They are moving away from Earth and are farther from Earth than galaxies with lower speeds.
what can we say about the galaxies measured from earth at low speeds?
They are moving away from earth and are closer to earth than galaxies with high speeds.
Suppose that galaxy B is twicw as far from Earth as galaxy A. Hubbles law predicts that galaxy B will be moving away from earth with approximatley _____.
twice the velocity of galaxy A.
True or False: Most Galaxies are spirals like the Milky Way
True or False: Most elliptical galaxies contain only young stars.
True or False: Type I supernovae can be used to determine distances to galaxies.
True or False: Active galaxies can emit thousands of times more energy than our own galaxy
Using the method of standard candles, we can, in principal, find the distance to a campfire if we know.
The number of logs used
About how many galaxies are within 30 mega parsecs of the sun
a few thousand
Hubble's Law states that
The greater the distance to a galaxy, the greater the galaxy's redshift.
If the light from a galaxy fluctuates in brightness very rapidly, the region producing the radiation must be
very small
Quasar spectra are
strongly redshifted
The flattest of ellipticals are class
what is common to spiral galaxies?
ongoing star formation and emission nebula in the arms
The astronomer who orginally classified galaxies into Spiral, Elliptical, and Irregular
Edwin Hubble
Compared to our own galaxy, elliptical galaxies
show no evidence of ongoing star formation
Large and small Magellanic Clouds fall into Hubble's Class
Irr I
The greatest variation in size mass and luminosity occurs in
elliptical galaxies
A galaxy with little cool gas or dust and no evidence of ongoing star formation is most likely a
Within the boundaries of the constellations Coma and Virgo are found in
the largest nearby superclusters of galaxies
What are Type I supernovae used for?
Standard candles for determining distances to other galaxies
Tully-Fisher relation exists between the galaxy's luminosity and its
According to Hubble's Law, a galaxy with a velocity of 25,000km/s will be
400 million parsecs away
According to Hubble's Law, the greater a galaxy's red shift, the
farther it is from us
The nearest lobe radio galaxy to our Milky Way is
Centaurus A
In active galaxies, their central engines may be temporarily fed by
a close encounter with a neighbor galaxy
The key to finding quasar's distances was
the huge red shifts of the hydrogen lines in 3C273
In what sense are the quasars "quasi-stellar"?
In short time exposures, their images looked stellar
True or False: Collisions between galaxies are rare and have little or no effect on the stars and interstellar gas in the galaxies involved
True or False: On the largest scales, galaxies in the universe appear to be arranged on huge sheets surrounding nearly empty voids.
A galaxy containing substantial amounts of dark matter will
Spin faster
The fraction of mass of the universe made up of dark matter is
more than 90%
Many nearby galaxies may have been
much more active in the past
As we look at larger and larger scales the universe we find
a larger and larger percentage of the matter is dark
Based on galactic rotation curves and cluster dynamics, we think of dark matter
comprieses of over 90% of the entire mass of the universe
A radio galaxy whose lobes are swept back as if forming a tail, what dose this probably indicate
This is evidence for intergalactic matter.
Collisions between galaxies is thought to
be commonplace
collisions between galaxies
cause the gas and dust clouds to collide, leading to rapid star formation
Where are large dust clouds predominately located in the galaxy M51?
Within or on the edges of the spiral arms
Where are the ionization nebulae predominately located in the galaxy M51?
Within or on the edges of the spiral arms of the galaxy
Why are the ionization nebulae so bright?
They are regions where gas is ionized by hot, young stars
True or False: Cepheid Variable can be used to determine the distances the nearest galaxies
True or False: The Galactic halo contains about as much gas and dust as the Galactic disk
True or False: Stars and Gas in the Galactic disk move in roughly circular orbits around the Galactic Center.
True or False: The most likely explanation of the high-speed motion of stars and gas near the Galactic center is that stars and gas are orbiting a supermassive black hole
In the Milky Way Galaxy, our sun is located
about halfway out from the center
The first stars that formed in the Milky Way now have
random orbits in the halo
Most of the mass of the milky way exists in the form of
dark matter
A cepheid variable star with a luminosity 1000 times that of the sun has a pulsation period of roughly
3 Days
In structure, our milky way is most similar to
The Andromeda Galaxy
The first attempt to map the Galaxy via star counts was done by
William Herschel in the late 18th century
The RR Lyrae stars all have periods of
a few hours
For finding the distances to globular clusters, Harlow Shapley used
RR Lyrae variables
Why was Herschel's for mapping the galaxy flawed?
He relied on on visual wavelengths, which are obscuredd by dust
What kind of variable stars would be classified as a RR Lyrae?
F giant with a period of 14 hours
The period luminosity relation is crucial in finding distances with
Cepheid Variables
Harlow Shapley found the Milky Way was
much larger than previously thought
Galactic Disks appear blue because of
O and B blue giants are much brighter than G, K, or M dwarfs
From the Sun, the distance to the Galactic Center is about
8 killa-parsecs
Detailed measurements of the disk and central bulge region of our galaxy suggest our Milky Way is a
Barred spiral galaxy
Between us and the Galactic Center, the Milky Way has a mass of
100 billion suns
In our location in the Milky Way, the galactic disk is only about ________ ly thick
What two observations allow us to calculate the galaxy's mass?
The suns orbital velocity and its distance from the Galactic Center
The dark halo is now believed to extend at least
50 Kila-parsecs
Most of the mass of the Milky way seems to exist in the form of
dark matter out in the halo
True or False: Herschel believed the Milky Way was a disk of stars, while Shapely found the extended halo more like a ball
True or False: Shapley found the globulars were strongly concentrated toward Sagittarius
True or False: Population I stars came billions of years before Population II stars
True or False: Stars within an emission nebula, such as M42, are considered Population I stars
True or False: The Globular star clusters are the most obvious examples of population II around us
The bright blue stars of Orion's Belt are Population I, while our Yellow Sun is population II
True or False: It would be very unlikely to find a massive, young star out in the halo
True or False: Like our solar system, the whole Milky Way is about five billion years old
True or False:The density wave theory attempts to explain why the spiral arm structure persist over a long time
True or False: Dark Matter has not been observed at any electromagnetic wavelength
During the history of the universe, what important event occurred about 0.001 seconds after the Big Bang?
Most matter in the early universe was annihilated by antimatter
What important event occurred earliest in the history of the universe
Space time rapidly expanded during a brief period of inflation
During the history of the universe, what important event occurred about 380,000 years after the Big Bang
Light began to travel freely through the universe.
Essentially all the hydrogen nuclei that will ever exist in our universe was created
by the time the universe was about 3 minutes old
Compared to when the cosmic microwave background was first released, the radiation of the cosmic microwave background today is
fainter and has most of its photons at longer wavelengths
when the universe was 10 years old, the density of radiation was
much greater than that of matter
The concept that on the grandest of scales, the universe is similar in appearance everywhere is
Because almost all galaxies show redshifted spectra, we know that
the universe is expanding.
If Euclid is right, then Omega is
The darkness of the night sky in an infinite universe is addressed in
Olbers's paradox
From the 1970s to the present, the accepted value of H has almost doubled, so
the age of the universe is half what we believed
In what model will the universe stop expanding
Closed Universe
If Omega is less than 1 then
the universe will expand forever
What is the meaning of a "closed" universe?
The universe will someday stop expanding and begin collapsing inward
The latest studies from ________ led to the discovery of "dark energy."
Type I supernovae at very large red shifts
What temperature has the Big Bang cooled to by now?
Just over 2.7K
The discovery of the cosmic microwave background was important because
it was was experimental verification of a prediction from the Big Bang theory
The Big Bang formed
hydrogen and helium, but nothing else
Why didn't elements heavier than helium form in the first minutes of creation?
When He-4 was formed, the expansion cooled the cosmos below 100 million K
The satellite that found the ripples in the cosmic background that led to galaxies is
True or False: In the cosmological principle, we can easily test cosmic homogeneity with the red shift surveys, but isotropy cannot be so tested.
True or False: It appears that nearly three times as much dark energy exists in the universe than normal and dark matter combined
True or False:Deuterium abundance suggests that normal matter makes up only 3-4% of the critical density.
True or False: The background hiss that Bell Labs detected was the best observational evidence for the Big Bang.