Chapter 13 Astronomy
What is the most likely way that one type of galaxy may be formed from others?
mergers
Which list below ranks the following features of an active galaxy in order of increasing distance from the center of the galaxy from left to right?
supermassive black hole, accretion disk, jet, radio lobe
What is at the center of Seyfert galaxies?
supermassive black holes
What does it mean that "quasars are most common at a redshift of about 2"?
that in the past there was a time of more galactic interaction
Edwin Hubble resolved the Shapley-Curtis debate in 1924 by measuring the distance to large, bright spiral nebulae. What distance method did Hubble employ?
the Cepheid variable star method
What must be known to estimate the distance to a galaxy with the Hubble law?
the Hubble constant and the recessional velocity
Which of the following is the least important factor in galactic evolution?
the elemental composition of the material from which galaxies form
Which is a way that quasars are similar to active galaxies?
All of these are similarities.
What gives elliptical galaxies a redder color than spiral galaxies?
Elliptical galaxies have less gas and dust.
With respect to measuring the properties of galaxies, select all of the correct statements from the following list.
Galactic clusters provide evidence of dark matter. Galactic clusters provide evidence of dark matter. Distance and radial velocity are related by the Hubble law. Stars at the center of galaxies orbit at very high velocities.
How was William Parsons (Lord Rosse) in 1845 able to see spiral structure in some nebulae, whereas others had not noticed this spiral structure before?
His 72-inch-diameter telescope was the largest in the world.
Time Scales. Which is the longest time scale?
Hubble
Which is true about the amount of time that objects take to appreciably change their brightness?
It cannot be in less time than light takes to cross its diameter.
What is the likely future of a starburst galaxy?
It will eventually run out of gas and dust for star formation.
With respect to the evolution of galaxies, select all of the correct statements from the following list
Large elliptical galaxies are formed by mergers. There is evidence that galaxies evolve by collisions and mergers. Collisions between galaxies trigger star formation. Spiral galaxies do not appear to be formed by mergers.
This is an image of the starburst galaxy NGC 1569. What is believed to be the cause of the recent rapid rate of star formation in this galaxy?
NGC 1569 has recently collided with another galaxy.
What assumption is made in determining mass by the rotation curve method, the cluster method, and the velocity dispersion method?
Newton's law of gravity is valid and that the system being measured is holding itself together
Would people living on a planet orbiting a star in an E0 type galaxy see a milky way?
No, their galaxy has no disk.
Why do you see only one jet in the radio image of a quasar?
One jet is directed more or less toward Earth and one jet is directed away from Earth.
A Sense of Proportion: Arrange the following in order of increasing size:
Our solar system , a dwarf galaxy , or Milky Way galaxy , a giant elliptical galaxy , a galaxy cluster
A Sense of Proportion: Arrange the following in order of increasing size:
Our solar system , our Milky Way galaxy , a giant elliptical galaxy , a pair of radio lobes around an active galaxy
Quasars have which of the following characteristics?
Quasars have bright emission-line spectra.
With respect to distant active galaxies and what they reveal about the history of the universe, select all of the correct statements from the following list.
Quasars may be what galaxies looked like when the universe was younger. Most quasars appear to have been involved in galactic mergers or collisions. Quasars appear as they looked a very long time ago. Quasars are thought to be active galaxies that are very far away.
The _____ subclass of spiral galaxies has the most tightly wound arms. The _____ subclass of spiral galaxies has the smallest nucleus.
Sa; Sc
Galaxies in close pairs are three times more likely to be Seyfert galaxies than are isolated galaxies. What general conclusion can be drawn from this statistical fact?
Seyfert galaxies are very likely the result of galaxy interactions.
What evidence is there that galactic cannibalism really happens?
Some galaxies appear to have multiple nuclei.
What does the location of the pink areas tell us?
Spiral arms are areas of active star formation.
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?
Supernovae Type Ia are more luminous.
Which galaxy is most likely to be a Seyfert galaxy? What does this suggest?
That galaxies that interact with others are more likely to be active.
What does the fluctuation of the brightness of a quasar over a short period of time suggest about them?
That they are small.
What is the difference between an E7 and S0 galaxy?
The E7 galaxy has no nuclear bulge.
What is the difference between S0 and Sa galaxies?
The S0 galaxy has no visible gas and the Sa galaxy has hot, bright stars.
What is the difference between an Sb and SBb galaxy?
The SBb galaxy has an elongated nucleus.
What is the difference between an Sa and Sb galaxy?
The Sa galaxy has a larger nucleus.
How does an Sa galaxy differ from an Sc galaxy?
The Sa galaxy has less gas and dust.
Why are the three very distant galaxies pointed out in this image (see white arrows) red in color?
The extreme recessional speed causes a large Doppler shift.
This image shows four quasars around a galaxy. The redshift of each of the four quasars is 0.0394 and greater than that of the galaxy. How should we interpret this photo?
The galaxy acts as a gravitational lens and the four quasar images are of the same quasar.
What observational evidence leads us to believe that AGNs contain supermassive black holes?
The gas in the disk is orbiting at high speeds and short-duration fluctuations in brightness limit the size of the object at the center of an AGN.
How can a quasar jet eject material at apparent superluminal speed?
The jet ejects material at nearly the speed of light almost directly toward Earth.
In the double-exhaust model, how does a double-lobed radio source form?
The lobes are inflated by bipolar jets of excited gas emerging from the central galaxy.
How does a model quasar account for the different components of quasar spectra?
The rapidly fluctuating continuous spectrum could come from the accretion disk of a black hole and less rapidly fluctuating emission lines could come from clouds of gas surrounding the core.
Based on evidence that some galactic nuclei are active, and with respect to the sources of energy and the triggers for the activity, select all of the correct statements from the following list.
The supermassive black holes at the center of most galaxies are dormant. Some spiral galaxies have active cores. The mechanism by which supermassive black holes eject jets is not well understood. Jets can be twisted by the motion of a galaxy through the intergalactic medium
In the illustration above, for the middle quasar z = 0.240, and for the bottom quasar z = 0.389. Which of the statements below is true about these two quasars?
The z = 0.389 quasar has the greater redshift and also the greater distance of the two.
With respect to families of galaxies, select all of the correct statements from the following list.
There are three basic types of galaxies. The halos of spiral galaxies appear reddish, and contain little star formation. Elliptical galaxies do not make new stars. The nature of galaxies was not always understood.
Why are most quasars so far away?
There is a greater volume of the universe that is far away than is nearby and quasars were more abundant in the past when galaxies were close together.
What causes the pink areas in the figure to be so bright?
There is light from newly-formed bright and hot stars exciting the gas.
How are the shapes of galaxies affected by collisions?
They are twisted and distorted by tidal forces.
How are the spectra of Seyfert galaxies different from most galaxies?
They have broad emission lines of highly ionized elements.
How do quasars resemble the AGN in Seyfert galaxies?
They have jets and pairs of opposing radio lobes and are small and very luminous.
What evidence do we have that quasars are small?
They have rapid fluctuations in brightness.
Seyfert galaxies have a spectrum with broad emission lines of ionized elements. What other unusual features do Seyfert galaxies have?
They have small, highly luminous nuclei that fluctuate rapidly.
What is the significance of spiral jets from galaxies?
They likely mean that the active galactic nucleus is in motion through the intergalactic medium.
Which of the following is true about supermassive black holes?
They represent about 0.5 percent of the mass of the nuclear bulge and there is no relationship between the mass of the supermassive black holes and the mass of the disks of galaxies.
What is the difference between Type 1 and Type 2 Seyfert galaxies?
Type 1 Seyferts are very luminous at ultraviolet wavelengths and at X-ray wavelengths.
What is a starburst galaxy?
a galaxy going through a burst of star formation
Which galaxy is most likely to be active?
a galaxy that has interacted with another galaxy relatively recently
Which galaxy is most likely to be a Seyfert galaxy?
a galaxy that is near another galaxy
What must actually be measured to use the Hubble law to determine the distance to a galaxy?
a galaxy's redshift
What fraction of spiral galaxies are Seyfert galaxies?
about 2%
In a few billion years, our own Milky Way may merge with the Andromeda Galaxy. Which type of galaxy is most likely to result from such a merger?
an elliptical galaxy
What observable property of a standard candle must be measured to determine its distance?
apparent magnitude
Where are all the "dead" quasars?
at the center of galaxies with very little matter flowing in
Why does the above radio image of a quasar look so much like a double-lobed radio source?
because quasars are distant active galaxies
What are the pink areas in the figure?
clouds of ionized hydrogen gas
When viewing a distant galaxy, the amount of look-back time in years is equal to which of the following?
distance to the galaxy in light years
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
What type of galaxy is the most likely result of a merger?
elliptical
Which type of galaxy has the largest range in both size and mass?
elliptical
How is a starburst galaxy likely to be formed?
from a galactic merger
What is "look-back time?"
how long the light from an object takes to reach us and the same as the distance in light-years to an object
What did William Parsons (Lord Rosse) think the spiral nebulae were?
island universes
What is needed to determine the mass of a galaxy by the rotation curve method?
orbital radii and period of stars
What is the most likely reason for the differences between Type 1 and Type 2 Seyfert galaxies?
probably due to the lack of lower-velocity gases in the Type 1 Seyfert galaxies
What feature is most likely shown in the radio image?
radio jets
What is the most likely cause of the activity shown in the radio image?
radio jets being left behind by a galaxy rapidly moving through the intergalactic medium
What is the Hubble law a relationship between?
the distance and recessional velocity of a galaxy
What parameter must we know to determine the linear diameter and luminosity of a particular galaxy?
the distance to the galaxy
What was the topic of the Shapley-Curtis Debate of 1920?
the location of the spiral nebulae
Which feature of a galaxy seems to be related to the mass of the galaxy's central supermassive black hole?
the size of the galaxy's central bulge
How is determining the mass of a galaxy by the rotation curve method similar to determining the masses of stars in binary systems?
the use of Kepler's third law
Which is not a good distance indicator to galaxies?
white dwarfs
Which of the following is NOT a distance indicator used in galactic astronomy?
white dwarfs
Galaxies with active star formation also have which of the following?
All of these choices are correct.
How does the intracluster medium help determine the nature of the galaxies in a cluster?
All of these choices are correct.
The name "quasar" is derived from the description "quasi-stellar radio source." In this image the quasar (center) appears star-like. How are quasars very different from stars?
All of these choices are correct.
What conditions can create broad emission lines of highly ionized elements?
All of these choices are correct.
What does a redshift of "2" mean for a quasar?
All of these choices are correct.
What evidence do we have that quasars are very far away?
All of these choices are correct.
Which is evidence that quasars are very far away?
All of these choices are evidence
What evidence can you cite that active galactic nuclei contain supermassive black holes?
All of these choices are evidence.
What evidence can you cite that radio lobes are inflated by jets from active galactic nuclei?
All of these choices are evidence.
Which is a more likely evolution of galaxies?
Both spiral to elliptical and elliptical to spiral are equally likely to occur
Here are the subclasses of elliptical galaxies: E1, E3, E5, E7. Which list below has them in order from roundest to most elongated, from left to right?
E1, E3, E5, E7
Why is look-back time not important for nearby galaxies?
Galaxies change very slowly.
What does the degree of gravitational lensing seen in this image indicate?
Galaxy clusters contain much more mass than is visible.
What does the flatness of the rotation curve shown here reveal about this galaxy?
It has a lot of nonluminous (dark) matter in its outer regions.
What is the Milky Way in our sky?
It is a bright band of light that goes around the entire sky and it is the disk of the galaxy of which we are a part.
