Questions and Answers
Which of these options correctly describe Seyfert galaxies? (Select all that apply)
_____ galaxies emit an immense amount of radiation, with most coming from lobes that can be millions of light-years long.
Radio
Which options correctly describe active galaxies? (Select all that apply)
Seyfert galaxies have an abnormally bright ______ at their centers, whereas radio galaxies create ______ of radio emission outside themselves.
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Match the terms to their definitions.
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_____ galaxies emit an immense amount of radiation from a region far less than a light-year across and have gas clouds moving thousands of kilometers per second.
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Which options correctly describe radio galaxies? (Select all that apply)
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A ______ is a form of active galaxy that can appear like a dim star when observed in visual wavelengths.
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What best describes the visual appearance of a quasar?
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_____ were originally mistaken to be dim stars, but are in fact active galaxies.
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In one quasar, the time for short-term fluctuations in brightness is three times longer than for a second quasar nearby. This means that the diameter of the first quasar is about _____ times that of the second one.
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Place the following astronomical objects in order by their typical distances from us (Place the closest object first and the most distant object last).
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Quasars ____ (Select all that apply)
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Select the properties that a unified model of active galaxies must be able to explain.
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Select all that are forms of active galactic nuclei (AGN).
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If you observe variation in the brightness of the core of an active galaxy or a quasar over a time period of a week, you can conclude that the ____.
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Place the following astronomical objects in order by their physical size, putting the largest at the top and the smallest at the bottom.
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To explain different kinds of active galaxies using a single model of the phenomena at the core, that model must be able to explain ____ (Select all that apply).
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Match the terms relating to active galactic nuclei (AGN) to their meanings.
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An active galaxy contains ____ (Select all that apply).
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Match the letters in the diagram that indicate viewing angles of an active galaxy with the kind of galaxy that is observed from that viewing angle.
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Match the labels on the diagram with the parts of an active galactic nucleus.
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Arrange the statements to describe how a supermassive black hole might form.
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How do astronomers explain the different kinds of active galaxies all being caused by supermassive black holes with huge accretion disks?
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An object can appear to be traveling faster than the speed of light if it ____ at nearly the speed of light.
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The graph shows a correlation between the mass of galaxy bulges and the central black hole. This relationship suggests that ____ (Select all that apply).
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Why do supermassive black holes form in the center of galaxies and not elsewhere?
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Nothing can actually travel faster than light, but geometry can sometimes make very fast moving material moving in jets appear to do so. This phenomenon is called _____ motion.
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Generally, the larger the black hole at the center of a galaxy, the ____ the total mass of the galaxy.
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How do astronomers detect cool intergalactic gas clouds?
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Match terms referring to galaxy groups with their definitions.
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What was the 'Great Debate' between Harlow Shapley and Heber Curtis about? (Select all that apply)
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Select the features of spiral galaxies.
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Which of the following can be part of a galaxy?
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_____ was one of the first to argue convincingly that the Milky Way is huge, but thought other galaxies were much smaller, nearby nebulas.
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_____ argued that the fuzzy, catalogued objects were really distant galaxies like the Milky Way.
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Shapley won his debate with Curtis over the nature of galaxies.
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Select the features of elliptical galaxies.
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Match the objects to where you find them in a spiral galaxy.
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_____ and _____ independently recorded the positions of many faint, diffuse objects later known to be galaxies while each systematically mapped the heavens.
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Match the descriptions to the appropriate type of galaxy.
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Select all of the following objects that you would not expect to find in an elliptical galaxy.
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You are comparing elliptical galaxies and using the Hubble tuning fork as a guide. One galaxy is very spherical, while the other is long and cigar-shaped. The classification for the long and cigar-shaped one is most likely a(n) ____.
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What do astronomers use Hubble's 'tuning fork' diagram for?
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Match the statements to describe the pros and cons of using Cepheid variable stars to measure the distances to galaxies.
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You are comparing spiral galaxies and using the Hubble tuning fork as a guide. One galaxy has tightly wound arms and a large central bulge, while the other has a more loosely wound appearance. The classification for the tightly wound one is most likely a(n) ____.
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The Hubble 'tuning fork' diagram shows how a galaxy evolves from an irregular to a spiral and then finally into an elliptical.
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You have measured the period of a Cepheid star in the Large Magellanic Cloud. What else do you need to measure in order to calculate the galaxy's distance?
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Select the methods for measuring galaxy distances that use standard candles.
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It's necessary that some of these methods overlap to verify this system of measurements which is called the ____.
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Select the reasons why astronomers use Cepheids to calculate distances to galaxies.
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Two Cepheids in two different galaxies have the same period. One is 100 times brighter than the other. What can you conclude?
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Match the terms relating to spectral shifts to their definitions.
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How does the Tully-Fisher method enable astronomers to calculate the distance to galaxies?
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The stepwise determination of intergalactic distances, where one method is used to calibrate another method, is known as the ____.
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Select the best explanation of why galaxies have redshifts that increase with distance.
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A shift of the absorption lines in a galaxy's spectrum toward longer wavelengths is known as ____.
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According to Hubble's law, the larger the redshift, the ____ a galaxy is moving away from us and the ____ its distance is.
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Match the terms in Hubble's law with their descriptions.
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Distant galaxies' redshifts are Doppler shifts.
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The diameter of a galaxy is measured in thousands of parsecs, or kiloparsecs. The distances to galaxies can be many millions of parsecs. Astronomers use the ____ as a convenient unit for such distances.
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When Hubble plotted the independently measured distances of galaxies against their apparent recession velocity based on redshift, he discovered that the farther away the galaxy was, the ____ it seemed to be moving ____ us.
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A spiral galaxy without a bar may change into a barred spiral as a result of a galactic interaction, but the bar may eventually dissipate.
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Match the name of each concept with its mathematical representation.
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A megaparsec is ____ parsecs.
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Select all the statements that are correct about Hubble's law.
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Select all the statements that could describe irregular galaxies.
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Select all the cases where Hubble's law would not apply to a galaxy.
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The activity shown in the center of this picture is ____.
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Why aren't all spiral galaxies barred galaxies?
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Match the galaxy phenomena with the kind of interaction that causes it.
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A small, patchy galaxy rich in gas and dust, with disorganized pockets of young stars would be a(n) ____ galaxy.
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What about the picture tells you that a galaxy interaction is taking place?
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Elliptical galaxies tend to contain mainly ____.
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Select the phenomena that are caused by galaxy-galaxy interactions.
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A medium-sized galaxy with a mixture of red and blue stars arranged in multiple, large, and asymmetric arcs spread over space is most likely a(n) ____.
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The image shows a map of gas found in a galaxy, with red regions indicating the highest density regions. Select all the choices that accurately describe this map.
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Spiral galaxies have active star-forming regions and so contain ____.
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Match the descriptions to the types of galaxies.
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Match the descriptions of gas found in galaxies to the type of galaxies that would contain it.
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Why don't we know what fraction of galaxies is made up by spirals, ellipticals, and irregulars? (Select all that apply.)
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Rank the types of galaxies based on the range of sizes, with the galaxies with the biggest range of size (in diameter and mass) at the top.
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In the Hubble Deep Field image, we see many small galaxies very far away and relatively few big ones. A census of closer galaxies shows larger and more structured galaxies on average. Why?
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How can the bulges of spiral galaxies be created through galaxy mergers?
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In total, there seem to be more spiral than elliptical galaxies. In what environment, however, do there seem to be a much higher fraction of ellipticals?
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The Hubble Deep Field project observed the same part of the sky for 100 hours. Why has it been helpful for astronomers studying the evolution of galaxies? (Select all that apply.)
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Which features of galaxies can be explained by galaxy mergers?
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A _____ occurs when galaxies collide and settle into a single larger galaxy; galactic _____ occurs when a large galaxy captures and absorbs a small galaxy.
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Match the results of galaxy collisions with the appropriate outcome.
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Select all that correctly describe the red and blue sequences of galaxies.
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Scientists have observed faint streams of stars extending out from the Milky Way's disk that indicate it has absorbed a number of dwarf galaxies. This is best referred to as ____.
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Select all of the answers that correctly describe the process by which spiral galaxies are converted into ellipticals.
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This image of a galaxy in a cluster shows ____.
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Select all the galaxy types that are more likely to be products of mergers or galaxy-galaxy interactions than they are to have originally formed as that type.
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What process is most responsible for galaxies to move from the blue to the red sequence?
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In a cluster of galaxies, a spiral galaxy collides with a neighbor. The spiral's disklike pattern of circular rotation has been disrupted. What will happen to this system?
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More elliptical galaxies than spirals are found in galaxy clusters, suggesting that in that environment, spirals can quickly be converted into elliptical galaxies. Why does this occur?
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_____ galaxies are galaxies whose nuclei emit abnormally large amounts of energy from a tiny core region.
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What features do Seyfert and radio galaxies have in common? (Select all that apply.)
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Study Notes
Great Debate
- Central topic: Whether spiral nebulas are independent galaxies or satellite systems of the Milky Way.
- Harlow Shapley believed the Milky Way was massive but thought spiral nebulas were smaller, nearby objects.
- Heber Curtis argued that these fuzzy objects were distant galaxies akin to the Milky Way.
Features of Galaxies
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Spiral Galaxies:
- Characterized by a flattened disk shape with arms containing pink HII regions and blue stars.
- Central area is densest, with a variety of stars, including young, hot stars.
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Elliptical Galaxies:
- Can be spherical or oval, contain primarily old, red stars and have very little gas or dust.
- Densest regions are also at the center.
Components of Galaxies
- Galaxies can contain globular clusters, black holes, dark matter, interstellar clouds, and stars.
Astronomers and Their Contributions
- Harlow Shapley and Heber Curtis contributed key ideas during the Great Debate.
- Charles Messier and William Herschel recorded numerous galaxies.
- Shapley made significant propositions on the structure of the Milky Way.
Hubble's Tuning Fork
- A diagram used to classify galaxy types, showing relationships and potential evolution among different galaxy forms (spiral, elliptical, irregular).
Measuring Distances to Galaxies
- Several methods rely on standard candles like Cepheid variables and supernova luminosity.
- Distance ladder: A system of overlapping methods to verify measurements.
Redshift and Hubble’s Law
- Redshift is used to measure how fast galaxies are retreating from Earth; the greater the redshift, the faster the galaxy moves away.
- According to Hubble’s law, a galaxy’s recession velocity (V) is directly proportional to its distance (d).
Galaxy Types and Interactions
- Galaxies can transition from spiral to elliptical through interactions, often leading to the loss of star-forming gas.
- Elliptical galaxies are more common in crowded cluster environments, whereas spirals are more abundant in less dense regions.
Active Galaxies
- Subtypes include Seyfert galaxies, characterized by extremely luminous nuclei and rapid brightness changes, and radio galaxies, known for their pronounced radio emission lobes.
- Active galaxies are often linked to galactic mergers and feature intense radiation and gas dynamics.
Mergers and Galaxy Evolution
- Galaxy collisions can lead to elliptical or irregular shapes, and star bursts when significant gas remains post-collision.
- The process of galactic cannibalism describes larger galaxies absorbing smaller ones, leaving faint trails of stars.
Galactic Structure and Composition
- Spiral galaxies consist of numerous gas and dust clumps, promoting ongoing star formation.
- Elliptical galaxies typically harbor older stars with minimal interstellar gas.
Observational Insights
- The Hubble Deep Field project provided extensive data on remote, smaller galaxies, enhancing understanding of cosmic evolution and structures.
- Observations can be used to track the transition from blue (young, star-forming) to red (older, quiescent) galaxies as they age or utilize gas resources.### Quasars
- Quasars were misidentified as dim stars due to their visual appearance but are actually active galaxies.
- They are among the oldest and most luminous objects in the universe, with significant distances from Earth.
- Quasars exhibit large redshifts, indicating their extreme distances; they contain supermassive black holes at their centers.
Active Galactic Nuclei (AGN)
- Active galaxies include various forms of AGN: Blazars, Quasars, and Seyfert galaxies.
- A unified model of AGN must explain energy emissions, variation in brightness, and presence of jets in galaxies.
- Key characteristics include an accretion disk of matter emitting X-rays and jets of gas emanating from the accretion disk.
Brightness Variation and Measurements
- Observable brightness fluctuations in the core of active galaxies over weeks indicate a core diameter about equal to the speed of light multiplied by the observation period.
- Observational angles from which AGN are viewed (i.e., directly into jets) can affect the classification of the galaxy type.
Formation and Growth of Supermassive Black Holes
- Supermassive black holes form from the remnants of massive stars that collapse after a supernova.
- They grow larger by absorbing interstellar matter, which increases their mass and allows them to attract even more matter.
Correlations and Relationships
- There is a correlation between the mass of galaxy bulges and their central black holes; larger bulges typically contain larger black holes.
- Supermassive black holes are primarily found in galactic centers, where interstellar gas is most accessible, leading to their extensive growth.
Observation Techniques
- Astronomers detect cool intergalactic gas clouds through absorption lines observed from distant quasars, enabling the study of these clouds.
Geometry and Motion
- Superluminal motion refers to the optical illusion where objects can appear to exceed the speed of light due to their nearly direct trajectory towards the observer.
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Description
Explore the historical discussions surrounding the classification of spiral nebulas and their relationship with the Milky Way. This quiz delves into the arguments of astronomers like Harlow Shapley and Heber Curtis, as well as the characteristics of spiral and elliptical galaxies. Test your knowledge on the features and components that make up these vast cosmic structures.