The Great Debate on Galaxies
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Questions and Answers

Which of these options correctly describe Seyfert galaxies? (Select all that apply)

  • They do not have bright nuclei
  • The emission from the nucleus is at many wavelengths of light (correct)
  • Rapid changes in brightness (correct)
  • Very luminous nucleus (correct)

    • _____ 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)

  • Being an active galaxy is related to galaxy mergers (correct)
  • They have no central brightness
  • About 10% of galaxies are active galaxies (correct)
  • They have abnormally bright central regions (correct)

    • Seyfert galaxies have an abnormally bright ______ at their centers, whereas radio galaxies create ______ of radio emission outside themselves.

    <p>nucleus, lobes</p> Signup and view all the answers

    Match the terms to their definitions.

    <p>Seyfert galaxy = A spiral galaxy with an extremely luminous nucleus Radio galaxy = An active galaxy that creates bright radio lobes on either side of itself Radio lobes = Radio-emitting regions that shine with synchrotron radiation Jets = Narrow beams of electrons shot out of a radio galaxy, creating radio lobes</p> Signup and view all the answers

    _____ 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.

    <p>Seyfert</p> Signup and view all the answers

    Which options correctly describe radio galaxies? (Select all that apply)

    <p>They have radio lobes that can be thousands of parsecs long</p> Signup and view all the answers

    A ______ is a form of active galaxy that can appear like a dim star when observed in visual wavelengths.

    <p>quasar</p> Signup and view all the answers

    What best describes the visual appearance of a quasar?

    <p>Almost starlike</p> Signup and view all the answers

    _____ were originally mistaken to be dim stars, but are in fact active galaxies.

    <p>Quasars</p> Signup and view all the answers

    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.

    <p>3</p> Signup and view all the answers

    Place the following astronomical objects in order by their typical distances from us (Place the closest object first and the most distant object last).

    <p>Globular cluster</p> Signup and view all the answers

    Quasars ____ (Select all that apply)

    <p>Have large redshifts, which indicate they are extremely distant</p> Signup and view all the answers

    Select the properties that a unified model of active galaxies must be able to explain.

    <p>The most powerful active galaxies are seen at large distances</p> Signup and view all the answers

    Select all that are forms of active galactic nuclei (AGN).

    <p>Quasars</p> Signup and view all the answers

    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 ____.

    <p>diameter of the core is a length about equal to the speed of light times a week</p> Signup and view all the answers

    Place the following astronomical objects in order by their physical size, putting the largest at the top and the smallest at the bottom.

    <p>Elliptical galaxy</p> Signup and view all the answers

    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).

    <p>Why some galaxies have stronger jets than others (or no jets)</p> Signup and view all the answers

    Match the terms relating to active galactic nuclei (AGN) to their meanings.

    <p>Supermassive black holes = Black holes containing millions of solar masses, found in galaxy nuclei Accretion disk = Material swirling around and eventually falling into a black hole Blazar = Kind of AGN seen by observing directly into an oncoming jet Seyfert galaxy = Spiral galaxy with an abnormally luminous nucleus Radio galaxy = Galaxy that emits much more radio energy than normal galaxies</p> Signup and view all the answers

    An active galaxy contains ____ (Select all that apply).

    <p>Jets of gas that extend above and below the accretion disk</p> Signup and view all the answers

    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.

    <p>A (Directly into jet) = Blazar B (jets viewed from side angle) = Radio galaxy C (viewing accretion disk) = Quasar or broadline seyfert D (dusty outer disk seen edge-on) = Narrow-line seyfert</p> Signup and view all the answers

    Match the labels on the diagram with the parts of an active galactic nucleus.

    <p>A = Jet B = Dust torus C = Supermassive black hole D = Accretion disk</p> Signup and view all the answers

    Arrange the statements to describe how a supermassive black hole might form.

    <p>A massive star dies near the center of a galaxy.</p> Signup and view all the answers

    How do astronomers explain the different kinds of active galaxies all being caused by supermassive black holes with huge accretion disks?

    <p>The kind of active galaxy seen depends on the direction it is observed from.</p> Signup and view all the answers

    An object can appear to be traveling faster than the speed of light if it ____ at nearly the speed of light.

    <p>is moving almost directly towards us</p> Signup and view all the answers

    The graph shows a correlation between the mass of galaxy bulges and the central black hole. This relationship suggests that ____ (Select all that apply).

    <p>The presence of the black hole seems related to the growth of the bulge during mergers</p> Signup and view all the answers

    Why do supermassive black holes form in the center of galaxies and not elsewhere?

    <p>In the centers of galaxies, they have access to the most interstellar gas and can grow very large.</p> Signup and view all the answers

    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.

    <p>superluminal</p> Signup and view all the answers

    Generally, the larger the black hole at the center of a galaxy, the ____ the total mass of the galaxy.

    <p>bigger</p> Signup and view all the answers

    How do astronomers detect cool intergalactic gas clouds?

    <p>By measuring absorption lines from cool gas clouds in the light from distant quasars.</p> Signup and view all the answers

    Match terms referring to galaxy groups with their definitions.

    <p>Galaxy group = A small collection of galaxies close together M31, M33, and the Milky Way = The three spiral galaxies in the Local Group Leo I = A dwarf galaxy member of the Local Group Magellanic Clouds = Satellites of our Galaxy</p> Signup and view all the answers

    What was the 'Great Debate' between Harlow Shapley and Heber Curtis about? (Select all that apply)

    <p>Whether spiral nebulas were like the Milky Way or tiny satellites of it</p> Signup and view all the answers

    Select the features of spiral galaxies.

    <p>Pink HII regions and blue stars define the arms.</p> Signup and view all the answers

    Which of the following can be part of a galaxy?

    <p>Dark matter</p> Signup and view all the answers

    _____ was one of the first to argue convincingly that the Milky Way is huge, but thought other galaxies were much smaller, nearby nebulas.

    <p>Shapley</p> Signup and view all the answers

    _____ argued that the fuzzy, catalogued objects were really distant galaxies like the Milky Way.

    <p>Curtis</p> Signup and view all the answers

    Shapley won his debate with Curtis over the nature of galaxies.

    <p>False</p> Signup and view all the answers

    Select the features of elliptical galaxies.

    <p>Densest at the center.</p> Signup and view all the answers

    Match the objects to where you find them in a spiral galaxy.

    <p>Disk = Arms, blue stars, dust Halo = Population II stars, dark matter</p> Signup and view all the answers

    _____ and _____ independently recorded the positions of many faint, diffuse objects later known to be galaxies while each systematically mapped the heavens.

    <p>Messier, Herschel</p> Signup and view all the answers

    Match the descriptions to the appropriate type of galaxy.

    <p>Spiral galaxy = Two or more arms winding out from the center Elliptical Galaxy = Smooth, featureless appearance with no visible spiral structure Irregular galaxy = Stars and gas clouds scattered in random patches Barred spiral galaxy = Arms emerge from the end of an elongated central region S0 = Disk shaped with no spiral arms.</p> Signup and view all the answers

    Select all of the following objects that you would not expect to find in an elliptical galaxy.

    <p>Density-wave arm structures</p> Signup and view all the answers

    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) ____.

    <p>E7</p> Signup and view all the answers

    What do astronomers use Hubble's 'tuning fork' diagram for?

    <p>As a convenient way to organize galaxy types and subtypes.</p> Signup and view all the answers

    Match the statements to describe the pros and cons of using Cepheid variable stars to measure the distances to galaxies.

    <p>Pro = Pulsation periods are easy to measure, the relationship between period and luminosity is well-calibrated (today), Cepheids are very bright stars. Con = They are only bright enough to use in relatively close galaxies. Unrelated = Cepheids have unusual spectral lines, Cepheids are never found in spiral galaxies.</p> Signup and view all the answers

    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) ____.

    <p>Sa</p> Signup and view all the answers

    The Hubble 'tuning fork' diagram shows how a galaxy evolves from an irregular to a spiral and then finally into an elliptical.

    <p>False</p> Signup and view all the answers

    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?

    <p>The brightness (B) for every Cepheid you measure a period for.</p> Signup and view all the answers

    Select the methods for measuring galaxy distances that use standard candles.

    <p>The supernova method</p> Signup and view all the answers

    It's necessary that some of these methods overlap to verify this system of measurements which is called the ____.

    <p>Distance ladder</p> Signup and view all the answers

    Select the reasons why astronomers use Cepheids to calculate distances to galaxies.

    <p>They are reliable standard candles because of the period-luminosity relationship.</p> Signup and view all the answers

    Two Cepheids in two different galaxies have the same period. One is 100 times brighter than the other. What can you conclude?

    <p>The brighter one is 10 times closer.</p> Signup and view all the answers

    Match the terms relating to spectral shifts to their definitions.

    <p>Doppler Shift = A change in the wavelength of spectral lines as a result of the motion of the observer or source Redshift = Shift of lines to longer wavelength Blueshift = Shift of lines to shorter wavelength Cosmological redshift = Redshift caused by the expansion of space</p> Signup and view all the answers

    How does the Tully-Fisher method enable astronomers to calculate the distance to galaxies?

    <p>Generally, more massive galaxies rotate faster. More mass typically implies more light, so rotation can be used to find the luminosity of a galaxy.</p> Signup and view all the answers

    The stepwise determination of intergalactic distances, where one method is used to calibrate another method, is known as the ____.

    <p>Ladder</p> Signup and view all the answers

    Select the best explanation of why galaxies have redshifts that increase with distance.

    <p>Since the beginning of the universe, space has been expanding in all directions and taking galaxies with it.</p> Signup and view all the answers

    A shift of the absorption lines in a galaxy's spectrum toward longer wavelengths is known as ____.

    <p>Redshift</p> Signup and view all the answers

    According to Hubble's law, the larger the redshift, the ____ a galaxy is moving away from us and the ____ its distance is.

    <p>Faster, larger</p> Signup and view all the answers

    Match the terms in Hubble's law with their descriptions.

    <p>V = The apparent recession velocity of a galaxy z = This term is no part of Hubble's law, but it is related to the recession velocity d = The distance to the galaxy H = Hubble's constant</p> Signup and view all the answers

    Distant galaxies' redshifts are Doppler shifts.

    <p>False</p> Signup and view all the answers

    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.

    <p>Megaparsec</p> Signup and view all the answers

    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.

    <p>Away from</p> Signup and view all the answers

    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.

    <p>True</p> Signup and view all the answers

    Match the name of each concept with its mathematical representation.

    <p>Hubble's law = V = H x d Standard-candle method = d = L / (4piB) Observed redshift = z = (λ_observed - λ_emitted) / λ_emitted Hubble's constant = H_0 = 70 km/sec per Mpc</p> Signup and view all the answers

    A megaparsec is ____ parsecs.

    <p>One million</p> Signup and view all the answers

    Select all the statements that are correct about Hubble's law.

    <p>Hubble's law does not work for nearby objects.</p> Signup and view all the answers

    Select all the statements that could describe irregular galaxies.

    <p>An interacting elliptical and spiral galaxies</p> Signup and view all the answers

    Select all the cases where Hubble's law would not apply to a galaxy.

    <p>A galaxy moving toward us</p> Signup and view all the answers

    The activity shown in the center of this picture is ____.

    <p>A burst of star formation as a result of a galaxy-galaxy interaction.</p> Signup and view all the answers

    Why aren't all spiral galaxies barred galaxies?

    <p>Even if all spirals form bars, the bar alignments can be temporary.</p> Signup and view all the answers

    Match the galaxy phenomena with the kind of interaction that causes it.

    <p>Galactic bar = A close encounter with a neighboring galaxy Ring galaxy = A head-on collision between two galaxies Long arcs of stars flung out of the galaxies = A glancing collision of two galaxies</p> Signup and view all the answers

    A small, patchy galaxy rich in gas and dust, with disorganized pockets of young stars would be a(n) ____ galaxy.

    <p>Irregular</p> Signup and view all the answers

    What about the picture tells you that a galaxy interaction is taking place?

    <p>The long tail sticking out of one of the galaxies.</p> Signup and view all the answers

    Elliptical galaxies tend to contain mainly ____.

    <p>Population II stars</p> Signup and view all the answers

    Select the phenomena that are caused by galaxy-galaxy interactions.

    <p>A central galactic bar</p> Signup and view all the answers

    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) ____.

    <p>Irregular galaxy that formed as a result of a spiral disrupted by an interaction.</p> Signup and view all the answers

    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.

    <p>It's most likely a radio emission map.</p> Signup and view all the answers

    Spiral galaxies have active star-forming regions and so contain ____.

    <p>Dense clumps of gas and dust to make stars.</p> Signup and view all the answers

    Match the descriptions to the types of galaxies.

    <p>Elliptical = The largest galaxies, 100 times the mass of the Milky Way, belong to this type. Irregular = Most of the smallest galaxies are this type; they are often satellites of larger galaxies. Spiral = Sizes range from a few kiloparsecs to a few tens of kiloparsecs.</p> Signup and view all the answers

    Match the descriptions of gas found in galaxies to the type of galaxies that would contain it.

    <p>Spiral = Many cold interstellar clouds, gas emits 21-cm radio emission, greater quantities of gas (though less than the mass in stars) Elliptical = Very hot gas, gas emits X-rays, smaller quantities of gas.</p> Signup and view all the answers

    Why don't we know what fraction of galaxies is made up by spirals, ellipticals, and irregulars? (Select all that apply.)

    <p>The fractions of different types change depending on if you look in crowded or sparsely populated regions.</p> Signup and view all the answers

    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.

    <ol> <li>= Ellipticals</li> <li>= Spiral galaxies</li> <li>= Irregular galaxies</li> </ol> Signup and view all the answers

    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?

    <p>Small galaxies tend to merge together to form big ones.</p> Signup and view all the answers

    How can the bulges of spiral galaxies be created through galaxy mergers?

    <p>When a spiral galaxy swallows a small companion, some of the new gas sinks to the spiral's center, building up the bulge.</p> Signup and view all the answers

    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?

    <p>Clusters, where galaxies are crowded together.</p> Signup and view all the answers

    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.)

    <p>Astronomers could see young galaxies soon after they were formed.</p> Signup and view all the answers

    Which features of galaxies can be explained by galaxy mergers?

    <p>Bent spiral arms</p> Signup and view all the answers

    A _____ occurs when galaxies collide and settle into a single larger galaxy; galactic _____ occurs when a large galaxy captures and absorbs a small galaxy.

    <p>Merger, Cannibalism</p> Signup and view all the answers

    Match the results of galaxy collisions with the appropriate outcome.

    <p>Very little gas and dust are left after the collision = An elliptical galaxy is formed Large amounts of gas and dust are left after the collision = A spiral galaxy is formed High-mass galaxies that have aged are this color. = These galaxies appear red Galaxies after mergers where much gas and dust are left are this color = These galaxies appear blue.</p> Signup and view all the answers

    Select all that correctly describe the red and blue sequences of galaxies.

    <p>Galaxies transition from the blue sequence to the red as they use up their gas by making stars.</p> Signup and view all the answers

    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 ____.

    <p>Galactic cannibalism.</p> Signup and view all the answers

    Select all of the answers that correctly describe the process by which spiral galaxies are converted into ellipticals.

    <p>Disk stars are moved onto orbits with random orientations.</p> Signup and view all the answers

    This image of a galaxy in a cluster shows ____.

    <p>Overlaid visible and X-ray images revealing gas stripped out of a spiral galaxy.</p> Signup and view all the answers

    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.

    <p>S0 galaxy</p> Signup and view all the answers

    What process is most responsible for galaxies to move from the blue to the red sequence?

    <p>Aging of stars after they use up the gas in a galaxy.</p> Signup and view all the answers

    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?

    <p>The spiral will eventually transition to an elliptical galaxy, losing its gas through stripping and star formation.</p> Signup and view all the answers

    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?

    <p>Galaxies orbit through the center of clusters, areas rich in gas which collides with, heats, and helps strip gas out of the spiral galaxies.</p> Signup and view all the answers

    _____ galaxies are galaxies whose nuclei emit abnormally large amounts of energy from a tiny core region.

    <p>Active</p> Signup and view all the answers

    What features do Seyfert and radio galaxies have in common? (Select all that apply.)

    <p>Some Seyferts have jets like radio galaxies.</p> Signup and view all the answers

    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

    • 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.
    • 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.

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