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Practice Exam 4

Terms in this set (41)

The speed of light is about ________________ (watch the units!)
1 ly/year
What is the diameter of the visible disk of the Milky Way Galaxy?
100,000 light years
We think there is a giant black hole in the center of our galaxy, with a mass of about 4 million solar masses. How have we determined this mass?
by watching individual stars orbit the black hole and using Kepler's laws to determine the mass
What is the main constituent of the giant molecular clouds in which stars are formed?
They are mainly cool hydrogen gas.
Reflection nebula are often present in star forming areas. What color do they appear and what are they caused by?
Blue due to dust
Where are most heavy elements made?
in stars and supernovae
The diagram above shows the period-luminosity relationship for Cepheid variables. Which of the following is true for a Cepheid that has a period of variation of about 10 days?
It has an intrinsic luminosity of about 3000 solar luminosities.
Why are Cepheid variable stars important?
Cepheid variables can be used as "standard candles" to find the distance to nearby galaxies.
The "Great Debate" in astronomy had to do with the size and nature of the Universe. What were the main issues?
The size of the Milky Way galaxy and its uniqueness in the Universe.
What discovery ended "The Great Debate"?
Hubble's calculation of the distance to Andromeda using Cepheid variable stars.
In units of km/s/Mpc, what is the value of the Hubble Constant?
70
Which of these statements about Hubble's classification scheme for galaxies is false?
It represents an evolutionary sequence for galaxies (e.g., type SBa galaxies slowly turn into type SBb).
A massive object can distort the light of more distant objects behind it through a phenomenon that we call ______________.
Gravitational lensing
The expansion of the Universe causes _____________ .
a cosmological redshift of distant galaxies
When the cosmic background radiation was first released in the Universe, it had a temperature of about ________ degrees K, which is in the infrared part of the EM spectrum.
3,000
Now the cosmic background radiation has a temperature of about ______ degrees K.
3
I observe a galaxy that is 100 million light years away. Which of the following do I see?
the light from the galaxy as it was 100 million years ago, and it is redshifted
Which of the following is NOT evidence in favor of the Big Bang theory?
The detection of supermassive black holes in the centers of most galaxies
The Big Bang predicts that the universe was initially 90 percent hydrogen and 10 percent helium by mass.
False
Most of the current star formation in the Milky Way occurs in globular clusters.
False
Choose the four statements about the different galaxy types that are true.
-The disks of spiral galaxies look blue in color due to their ongoing star formation.
-You can often find a giant elliptical galaxy at the center of a rich cluster.
-Elliptical galaxies usually lack a significant amount of gas and current star formation.
-Irregular galaxies were quite common in the early Universe and many are still around today, including at least two that orbit our own Milky Way galaxy.
Match the person to their accomplishment.
-Developed a catalog of objects to avoid mistaking them for comets.
-Who developed the period-luminosity relation for Cepheid variable stars?
-Took part in the great debate, arguing that "spiral nebula" were in fact objects outside of our own Milky Way.
-Who found evidence for dark matter in the rotation curves of galaxies?
-Found the distance to the Andromeda Galaxy.
-Charles Messier
-Henrietta Levitt
-Heber Curtis
-Vera Rubin
-Edwin Hubble
Matching Question: for questions 46-50, match each galaxy image to its classification type.
-One of the Magellanic Clouds (Jackson polluck-esk)
-Has a bar in its central region.(looks like a poohole)
-Would likely have a yellow-orange color. (looks like an elliptical galaxy)
-An Sa galaxy (Looks like a UFO)
-Looks much like our Milky Way (if it doesn't have a bar)
-D
-A
-E
-B
-C
When looking at a Hubble diagram of velocity vs. distance, the steeper the slope of the line that fits the points, the [x] (higher/lower) the value of H0 and the [y] (faster/slower) the expansion of the Universe.
x=high
y=fast
According to current observations, it looks like the Universe will continue to expand forever at its current rate.
False
In astronomy, we use different methods for determining the distances to objects out in the Universe, building a "distance ladder", with each step relying on the previous step. Below, match the type of object to the method we commonly use to find its distance, keeping in mind the building of the distance ladder. In other words, you might be able to use several methods to find the distance to an object, but match the object to the technique that we perhaps first used to find a reliable distance to it.
-planets in the solar system
-relatively nearby stars
-stars in nearby galaxies
-supernovae in distant galaxies
-a very distant quasar
-radar ranging or spacecraft telemetry
-stellar parallax
-the Leavitt relation for Cepheid variable stars
-a "standard candle" method where we assume a luminosity for the object based on its physical properties and then measure its brightness
-the redshift of features in the object's spectrum
Galaxies are not stationary and are flowing toward the densest regions of space.
True
Why is the rotation curve of the Milky Way flat even out to distances beyond the visible disk?
Because most of the mass in the galaxy is not concentrated near the center and there is even a lot of matter that we can't see.
The disks of spiral galaxies don't contain any old stars, only new, blue stars.
False
Do spiral galaxies show evidence of abundant amounts of dust and gas?
Yes
Which type of galaxy is likely to contain K and M-spectral type stars but not O and B stars?
elliptical
n the graph above which represents our current picture of the evolution of the Hubble constant with time, portion [x] (A, B, or C) of the graph contains galaxies from which we receive light that was emitted furthest from our present time and has a [xa] (low/high) expansion rate. Portion [y] (A, B, or C) of the graph corresponds to more recent times and has a [ya] (lower/higher) expansion rate.
x=C
xa=low
y=A
ya=high
Match the letter to the marked structure in our Milky Way galaxy.
-letter a
-letter b
-letter c
-letter d
-letter e
-globular cluster
-galactic bulge
-nucleus
-galactic disk
-the halo
True or False: Given that the Sun is 2% "metals" by mass, the Sun probably formed from a cloud of gas that was enriched by previous generations of stars.
True
How do astronomers map the cold neutral hydrogen in galaxies?
By observing the 21cm radio line resulting from the spin-flip of the electron orbiting the proton.
What are the red regions in this picture?
Ionization (or emission) nebula which contain hydrogen gas excited by star formation.
What is the name of radio source in our galactic center?
sag
What is the name of the small group of galaxies that the Milky Way is a member of?
The Local Group
How do we estimate the age of the Universe?
By taking the inverse of the Hubble Constant.
Given our current understanding of the overall geometry of the Universe, we think the curvature is _______.
Flat
Match the type of matter or energy in the Universe with how much of that type the Universe contains.
-normal matter in stars
-normal matter in gas
-dark matter
-dark energy
-1%
- (-4%)
- (-25%)
- (-70%)
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