Chapter 17 Galaxies

A megaparsec is ____ parsecs.

one million

This image of a galaxy in a cluster shows ____.

overlaid visible and X-ray images revealing gas stripped out of a spiral galaxy

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

In the centers of galaxies, they have access to the most interstellar gas and can grow very large.

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

1. A massive star dies near the center of a galaxy. 2. After the supernova, a black hole forms 3. The black hole swallows interstellar matter. 4. Through the swallowing of matter, the mass and radius of the black hole increase, making it easier to swallow more interstellar matter faster. 5. Eventually the black hold swallows several million stars worth of matter.

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

1. Elliptical galaxy 2. Dwarf galaxy 3. Globular cluster 4. Quasar 5. Planet

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.

1. Ellipticals 2.Spiral galaxies 3. Irregular galaxies

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

1. Planets 2. Globular cluster 3. Galaxy cluster 4. Quasar

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.

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

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

A central galactic bar Ring galaxies Starburst galaxies Irregularly shaped galaxies

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

A- Jet B- dust torus C- supermassive black hole D- accretion disk

Match the parts of radio galaxies to the components labeled in the figure.

A- Radio lobe B- Jet C- elliptical galaxy

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

Aging of stars after they use up the gas in a galaxy.

What best describes the visual appearance of a quasar?

Almost starlike

Select all the statements that could describe irregular galaxies.

An interacting elliptical and spiral galaxies A dwarf galaxy without coherent structure, such as the Small Magellanic Cloud A pair of high-mass, interacting spiral galaxies, such as "The Antennae" galaxies.

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

As a convenient way to organize galaxy types and subtypes

Select all that correctly describe active galaxies.

Being an active galaxy is related to galaxy mergers. About 10% of galaxies are active galaxies. They have abnormally bright central regions.

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. (Please enter a number or fraction.)

Blank 1: 3

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

Blank 1: Active

Enter the last names of astronomers to complete the following sentences: and independently recorded the positions of many faint, diffuse objects later known to be galaxies while each systematically mapped the heavens.

Blank 1: Messier Blank 2: Herschel

Enter the last names of astronomers to complete the following sentences: was one of the first to argue convincingly that the Milky Way is huge, but thought other galaxies were much smaller, nearby nebulas. argued that the fuzzy, catalogued objects were really distant galaxies like the Milky Way.

Blank 1: Shapley Blank 2: Curtis

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

Blank 1: faster, quicker, or longer Blank 2: larger, greater, or farther

The diameter of a galaxy is measured 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.

Blank 1: megaparsec

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

Blank 1: merger Blank 2: cannibalism

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

Blank 1: nucleus or core Blank 2: lobes or regions

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

Blank 1: quasar

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.

Blank 1: superluminal

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

Blazars Quasars Seyfert galaxies

How do astronomers detect cool intergalactic gas clouds?

By measuring absorption lines from cool gas clouds in the light from distant quasars

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?

Clusters, where galaxies are crowded together.

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

Disk stars are moved onto orbits with random orientations. Mergers can cause spiral galaxies to turn into elliptical galaxies.

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

Disk- Arms, blue stars, dust Halo- Population II stars, dark matter

Match the terms relating to spectral shifts to their definitions.

Doppler Shift- A change in the wavelength of spectral lines as a result of motion of the oberver 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

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) ____.

E7

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.

Elliptical galaxy S0 galaxy Spiral galaxy

In the Hubble Deep Field image, we see many, 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?

Small galaxies tend to merge together to form big ones.

Match the descriptions to the types of galaxies.

Elliptical- the largest galaxies, 100 times the mass of the Milky Way, belong to this type Some of the dwarf galaxies in this group are about the size of globular clusters. Irregular- Most of the smallest galaxies are this type; they are often satellites of larger galaxies, The larger galaxies of this tpe-objects perhaps roughly the size of the milky way-were usually previously galaxies of other types but have been modified by interaction Spiral- Sizes range from a few kiloparsecs to a few tens of kiloparsecs.

Why aren't all spiral galaxies barred galaxies?

Even if all spirals form bars, the bar alignments can be temporary.

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

Galatic 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

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?

Galaxies orbit through the center of clusters, areas rich in gas which collides with, heats, and helps strip gas out of the spiral galaxies.

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

Galaxies transition from the blue sequence to the red as they use up their gas by making stars. They describe a relationship between a galaxy's color and its mass. Galaxies transition from the blue sequence to the red as they get older.

Match terms referring to galaxy groups with their definitions. (Some descriptions match more than one object, but there is only one correct set of matches.)

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

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

Generally, more massive galaxies rotate faster. More mass typically implies more light, so rotation can be used to find the luminosity of a galaxy.

Which of the following can be part of a galaxy?

Globular clusters Black holes Dark matter Interstellar clouds Stars

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.)

Hubble observations have high angular resolution, so astronomers can make out details in distant galaxies. Astronomers could see young galaxies soon after they were formed. Galaxies that are 10 billion light-years away appear as they were 10 billion years ago.

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

Hubble's law relates the distance of a galaxy from Earth and its recessional velocity. Hubble's law does not work for nearby objects.

Match the name of each concept with its mathematical representation.

Hubbles law- V= hxd Standard-candle method- dg= Lc4piBc Observed redshift- z= Hubble's constant- h0=7 0 km/sec per Mpc

The stepwise determination of intergalactic distances, where one method (such as Cepheids) is used to calibrate another method (such as Tully-Fisher), which is then used at farther distances, is known as the distance . Listen to the complete question

Ladder

Select the features of spiral galaxies.

May appear generally rounded or thin and elongated on the sky. A flattened disk of stars Pink HII regions and blue stars define the arms Densest at the center

Select the features of elliptical galaxies.

May be spherical or oval or egg shaped Densest at the center Generally old, red stars Little to no gas or dust

Match the astronomers with their contributions to the study of galaxies.

Messier- Located and cataloged many galaxies Herschel- Began a project to systematically map the sky and discovered many galaxies Shapley- Proposed a model describing the shape of the Milky Way Galaxy Curtis- Proposed that spiral nebulas were galaxies like our own Milky way

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

One galaxy in orbit around another galaxy A galaxy very close to our own Milky Way A galaxy moving toward us

Elliptical galaxies tend to contain mainly ____. (Select all that apply.)

Population II stars low-density gas

Match the statements to describe the pros and cons of using Cepheid variable stars to measure the distances to galaxies. Match statements that are not relevant or are incorrect to "unrelated."

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

____ were originally mistaken to be dim stars, based on their visual appearance, but are in fact active galaxies.

Quasars

____ galaxies emit an immense amount of radiation, with most coming from lobes that can be millions of light-years long.

Radio

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) ____.

Sa

____ 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.

Seyfert

Match the terms to their definitions.

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

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

Since the beginning of the universe, space has been expanding in all directions and taking galaxies with it.

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

Some active galaxies are powerful radio emitters, but others are not. Large amounts of energy come from a very small region, in a wide range of wavelengths. The most powerful active galaxies are seen at large distances.

Match the descriptions to the appropriate type of galaxy. (There is only one arrangement that is correct for all the choices.)

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.

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

Spiral- many cold interstellar clouds, gas emits 21-cm radio emission, greater quatities of gas (though less than the mass in stars) Elliptical- very hot gas, gas emits x-reyas, smaller quantities of gas.

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

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

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

The brighter one is 10 times closer.

Select all that correctly describe Seyfert galaxies.

The emission from the nucleus is at many wavelengths of light. Very luminous nucleus Rapid changes in brightness

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

The fractions of different types change depending on if you look in crowded or sparsely populated regions. Dim, small galaxies are hard to see at large distances.

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

The kind of active galaxy seen depends on the direction it is observed from.

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

The long tail sticking out of one of the galaxies

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?

The spiral will eventually transition to an elliptical galaxy, losing its gas through stripping and star formation.

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.

The stream shapes indicate the arms of a spiral galaxy. It's most likely a radio emission map.

Select the methods for measuring galaxy distances that use standard candles (that is, being able to use actual luminosity and apparent brightness to find the distance).

The supernova method The Cepheid method The Tully-Fisher method

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

They are extremely luminous and therefore easy to see even at large distances. They are reliable standard candles because of the period-luminosity relationship.

Select all that correctly describe radio galaxies.

They emit radio waves because of electrons moving near the speed of light in a magnetic field. Some emit millions of times more energy in radio waves than ordinary galaxies. They have radio lobes that can be thousands of parsecs long.

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

They have extremely luminous nuclei. Some Seyferts have jets like radio galaxies.

Which features of galaxies can be explained by galaxy mergers?

Twisted galaxy disks Bursts of star formation Streams of stars around larger galaxies Bent spiral arms

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

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

Match the results of galaxy collisions with the appropriate outcome.

Very little gas and dust are left after the collisioon- 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.

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

When a spiral galaxy swallows a small companion, some of the new gas sinks to the spiral's center, building up the bulge.

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

Whether spiral nebulas were like the Milky Way or tiny satellites of it The size of the Milky Way Galaxy The likely distances of spiral nebulas

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

a burst of star formation as a result of a galaxy-galaxy interaction

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

an accretion disk of matter with fast-orbiting gas that emits X rays jets of gas that extend above and below the accretion disk a supermassive black hole

Quasars ____. (Select all that apply.)

are some of the oldest objects in the Universe are extremely distant objects are very small objects located at the centers of galaxies have large redshifts, which indicate they are extremely distant are some of the most luminous objects in space

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. (Select two choices.)

away from faster

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

bigger

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

dense clumps of gas and dust to make stars

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

density-wave arm structures a dark nebula blue main sequence stars

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 ____.

diameter of the core is a length about equal to the speed of light times a week

Astronomers have several different methods to measure the distances to galaxies, including using different kinds of standard candles, the Tully-Fisher method, methods based on galaxy appearance, and even parallax to study standard candles themselves. It's necessary that some of these methods overlap to verify this system of measurements which is called the ____.

distance ladder

True or false: Distant galaxies' redshifts are Doppler shifts.

f

True or false: Shapley won his debate with Curtis over the nature of galaxies.

f

True or false: The Hubble "tuning fork" diagram shows how a galaxy evolves from an irregular to a spiral and then finally into an elliptical.

f

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 _____.

galactic cannibalism

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

irregular

A medium sized galaxy with a mixture of red and blue stars arranged in mutliple, large, and asymmetric arcs spread over space is most likely a(n) _____.

irregular galaxy that formed as a result of a spiral disrupted by an interaction

An object can appear to be traveling faster than the speed of light, that is, showing superluminal motion, if it ____ at nearly the speed of light.

is moving almost directly towards us

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

redshift

True or false: 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.

t

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?

the brightness (B) for every Cepheid you measure a period for

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

the presence of the black hole seems related to the growth of the bulge during mergers larger bulges house larger black holes

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.)

why some galaxies are not active, especially more of the nearby, older galaxies why some galaxies have stronger jets than others (or no jets) how both spiral and elliptical galaxies can have active cores