PHYS, Stars & Galaxies, Chap. 24, Homework & Test Review, Prof. Kaim, DMC
Which type of supernovae all have about the same luminosity?
Type I
What is the nearest galaxy cluster to the Local Group?
Virgo Cluster - containing about 3,500 galaxies
A certain quasar has a redshift of 0.25 and an apparent magnitude of 13. Part B Calculate the quasar's luminosity. Express your answer using two significant figures.
Where M = -27 10^((-0.4)x((M)-4.85)) 10^((-0.4)x((-27)-4.85)) = 5.4954087x10^12 = 5.4x10^12 solar luminosities
What is a group of galaxies held together called?
a galaxy cluster
What does the spectral line of an normal galaxy look like?
a steady rise followed by a steep descent
According to Hubble's Law, a galaxy 500 million parsecs away has a velocity of roughly a) 25,000 km/s away from us. b) 75,000 km/s toward us. c) 35,000 km/s away from us. d) 35,000 km/s toward us.
c) 35,000 km/s away from us.
What did the discovery suggest to cosmologists? a) The universe is static. b) The universe is collapsing. c) The universe is expanding. d) The universe is contracting. e) There is no accepted interpretation.
c) The universe is expanding.
How would we get distances to more distant galaxies (tens of megaparsecs) without using the Hubble law? a) trig parallax b) period-luminosity relation for Cepheids c) comparing brightest stars/clusters/nebulae with similar objects in Milky Way d) main sequence fittinge) impossible to do it
c) comparing brightest stars/clusters/nebulae with similar objects in Milky Way
How far away can scientists find the distance of a star?
about 1 Gpc
Black holes and neutron stars
absorbs material, material crushes down in the accretion disk, and the accretion disk emits energy
The further a galaxy is away from us, the more redshifted and the ___________ it flies away.
faster
What is recession velocity?
how fast a galaxy is moving away from us
Rotation speeds can be determined by
how much the spectral lines widen.
When wavelengths get ___________ their light gets redder, when wavelengths get ___________ their light gets bluer.
longer; shorter
Rotation speeds define the amount of energy and ___________ of a galaxy as a whole.
luminosity
How do active and normal galaxies differ?
luminosity type of radiation emitted
Are there two different mechanisms of formation of the radio galaxies?
no
Tully-Fisher relation
relates the rotation speeds of the entire galaxy to their luminosities the faster the star rotates, the more energy it carries
What does the spectral line of an active galaxy look like?
slight peak with a fairly straight line
What type of galaxy is the Milky Way?
spiral barred type B (SBb)
Accretion disks are formed by
swallowing in the material from the galaxy - stars NOT gas and dust
Intrinsic Brightness (Luminosity)
the amount of energy that the star radiates per second in all directions, also referred to as absolute brightness or absolute magnitude.
What are the classifications of a spiral galaxy?
the central bulge relative to the spirals themselves Sa - large - large bulge, neatly wound arms Sb - medium - smaller bulge, loose spiral arms Sc - small - even smaller bulge, spirals even less small
How many spiral galaxies are in the Local Group?
three (Milky Way, Andromeda, M33)
Blueshifted means that it is moving ________ the source and is ________.
towards; negative
What does edge-on mean?
we cannot see the spiral arms, as we can only view the edge (Ex. Sombrero Galaxy)
Part D According to Hubble's law, with H0 = 70 km/s/Mpc , how far away is a galaxy whose recessional velocity is 4000 km/s ? Express your answer using two significant figures.
4,000/70 = 57.1428571 D = 57 Mpc
Part F If H0 = 85 km/s/Mpc ? Express your answer using two significant figures.
4,000/85 = 47.0588235 D = 47 Mpc
A Cepheid variable star in the Virgo cluster has an absolute magnitude of -5 and is observed to have an apparent magnitude of 26.3. Use these figures to calculate the distance to the Virgo cluster.
Formula d = (10pc)(10^((m-M)/5) Steps 1) ((26.3--5)/5) = 6.26 2) (10pc)(10^6.26) = 18197008.5861 3) 1.8x10^7
Using the method of standard candles, we can, in principle, find the distance to a campfire if we know a) the length of time the fire has been burning. b) the type of wood used in the fire. c) the fire's temperature. d) the number of logs used.
d) the number of logs used.
Part B How does this answer change if H0 = 55 km/s/Mpc? Express your answer using two significant figures.
55x180 = 9,900 v-rec = 9900 km/s
Spiral galaxies are filled with what types of stars?
B and G, appear white-ish
According to Hubble's Law, if Galaxy A is 10 times farther away than Galaxy B, we should observe Galaxy A to be moving a) 100 times faster than B away from us b) 10 times faster than B away from us c) 10 times faster than B toward us d) 100 times faster than B toward us
b) 10 times faster than B away from us (It is in this way that Hubble's Law allows us to calculate the distance to a galaxy if we observe the amount of redshift in its spectrum.)
What is the H in V = Hr? a) Cepheid relation b) Hubble constant c) radial velocity d) distance in megaparsecs e) Wien's constant.
b) Hubble constant
We estimate the value of H by getting what measure for many galaxies at many different (Doppler redshift) recession velocities? a) temperature b) luminosity c) distance d) color e) size
c) distance
"What if a galaxy was not tilted but was positioned toward us perfectly face-on, so stars in the galaxy are neither approaching nor receding from us, from our point of view. Would the Tully-Fisher technique work? a) Yes, the galaxy is still rotating, so we will measure a Doppler shift. b) No, the light from the center of the galaxy would be too bright. c) Yes, we can see the galaxy swirling in the sky. d) No, there is no motion towards or away from us. In this case, there is no Doppler shift we can measure.
d) No, there is no motion towards or away from us. In this case, there is no Doppler shift we can measure.
What is the most likely source of energy for active galaxies and quasars? a) collisions of large spiral galaxies b) large clusters of very massive, luminous stars c) a single supermassive, superluminous star d) accretion onto a supermassive black hole e) numerous supernovae from rapid star formation in large galaxies
d) accretion onto a supermassive black hole
What forms the typical lenticular galaxy?
- lens-shaped - central bulge - disk not well-formed - no spiral arms - S0 (lenticular) and SB0 (lenticular barred)
The following figures give the approximate speeds at which five galaxies are moving away from Earth due to the expansion of the universe. Rank the galaxies based on their distance from Earth, from farthest to closest. a) 5,264 km/s b) 18,730 km/s c) 45,000 km/s d) 130,000 km/s e) 1,577 km/s
Farthest d) 130,000 km/s c) 45,000 km/s b) 18,730 km/s a) 5,264 km/s e) 1,577 km/s Closest (Again, we see Hubble's law in action: more distant galaxies move at higher speeds.)
Use the data in the table to estimate the absolute magnitude of a quasar with a redshift of 5 and an apparent magnitude of 20.0. Express your answer using three significant figures. Redshift v/c Present Distance Look-BackTime (Mpc) (106 ly) (mill. of yrs) 5.000 0.946 8000 26,100 12,600
M = -24.5 L = 5.5x10^11
The spectral lines of quasars are a) emission lines with large redshifts. b) a continuum from the synchrotron radiation. c) fuzzy absorption lines from the merged light of the billions of stars. d) too complex for any interpretation.e) nonexistent, the gas is too hot to be totally ionized, so no lines are seen.
a) emission lines with large redshifts.
Which type of galaxy most resembles our Milky Way? a) spiral b) globular c) irregular d) elliptical e) lenticular
a) spiral
Spectral lines from a Seyfert galaxy are observed to be redshifted by 0.4 percent and to have broadened emission lines indicating an orbital speed of 270 km/s at an angular distance of 0.1 ′′ from its center. Part A Assuming circular orbits, use Kepler's laws to estimate the mass within this 0.1 ′′ radius. (Sec 23.6 in the textbook) Express your answer using one significant figure.
d = 0.1"x2π(16x10^6)/360x3,600 d = 7.75702 AU (206,265 AU= 1 pc) 7.75702 AU x 206,265 AU = R= 1588240.5 or 1.6x10^6 p = 2πR/v 2π(1.6(10^6)x((1.4(10^8))/270) = p = 5.21272x10^8sec/31,556,900 sec/yr p = 165185 or 1.65x10^5 solar mass = d^3/p^2 (1.6x10^6)^3/(1.65x10^5)^2 = 1.5045x10^8 sol mass 1 solar mass = 2x10^30 kg (1.5045x10^8)x(2x10^30) = 3.009x10^38 kg = 3x10^38 kg
Which type of galaxy contains the most Population II stars? a) spiral b) globular c) irregular d) elliptical
d) elliptical
What are starburst galaxies?
galaxies that are producing new stars at very high rates, as much as 100 times that of our galaxy (more luminous galaxies)
What are quasars?
- at furthermost part of the galaxy - oldest type of galaxies in the Universe - emit a large amount of energy - most luminous extreme stars with strong radio waves.
What forms the typical elliptical galaxy?
- millions to trillion of stars - vary in size from dwarf to giant - contain very little if any cool gas and dust - have large clouds of hot gas extending beyond the visible galaxy - no evidence of ongoing star formation
What is a Cepheid variable and how is it used?
- searching for stars in a galaxy with a repeatable cycle - overlay rotation speeds with their luminosity - defined by the rotation of stars - find the distance by calculating the absolute luminosity
What forms the typical spiral galaxy?
- the disk is thin and are formed by the spiral arms; - the core is surrounded by a halo of gas and dust; - which forms the central mass called a bulge - the space between (interstellar) is filled with cold gas - ongoing star formation
Part C - Types of radiation Active galactic nuclei can produce electromagnetic radiation from low-frequency radio wavelengths to high-frequency X-ray wavelengths. Some of this radiation comes from "thermal" sources involving material that has been heated to some characteristic temperature. Other radiation comes from "nonthermal" sources involving charged particles spiraling around magnetic field lines at speeds close to the speed of light. Here, the radiation that is emitted has nothing to do with the temperature of the source. Scientists have been able to reproduce this latter type of radiation in particle accelerators known as synchrotrons. For this reason, nonthermal radiation is often called "synchrotron radiation." Identify which emission properties relate to thermal and synchrotron (nonthermal) radiation. 1. ____________ radiation peaks at a characteristic frequency. 2. ____________ radiation is consistently stronger at lower frequency (longer wavelength). 3. ____________ radiation depends on the temperature of the source. 4. ____________ radiation depends on the presence of magnetic fields.
1. Thermal 2. Synchrotron 3. Thermal 4. Synchrotron (Whenever a charged particle encounters a magnetic field, the particle tends to spiral around the magnetic field lines (see the figure below). As it does, it emits electromagnetic radiation. Radiation produced in this way is called synchrotron radiation. The radiation is nonthermal, which means there is no link between the emission and the temperature of the radiating object. Virtually all of the energy emitted from a magnetized jet is synchrotron radiation.)
Astronomers observe galaxies and categorize them according to four different kinds of shapes: elliptical, spiral, barred-spiral, and irregular. In addition to shape, each of the four different galaxy types can be described by other common characteristics. (Match the following characteristics with their corresponding galaxy type.) a) Central bulge, flattened disk, spiral arms, gas, dust, young stars. b) Asymmetric, often with gas, dust, and young stars. c) Elongated central structure, flattened disk, spiral arms, gas and dust, young stars. d) Round, no disk, very little gas and dust, only old stars.
Elliptical galaxy (E) d) Round, no disk, very little gas and dust, only old stars. Spiral galaxy (S) a) Central bulge, flattened disk, spiral arms, gas, dust, young stars. Barred-spiral galaxy (SB) c) Elongated central structure, flattened disk, spiral arms, gas and dust, young stars. Irregular galaxy (Irr) b) Asymmetric, often with gas, dust, and young stars. (Each of the four basic galaxy types is readily recognizable by its apparent shape. Astronomers have since learned that elliptical galaxies contain mostly old, red stars and very little gas or dust. Spiral and barred-spiral galaxies have central bulges typically containing old stars along with flattened disks, which harbor both old and new stars as well as clouds of gas and dust. Irregular galaxies lack the symmetric structure seen in the spiral and elliptical galaxies. Some irregular galaxies are rich in gas and dust and are the sites of vigorous star formation.)
The following figures give the approximate distances of five galaxies from Earth. Rank the galaxies based on the speed with which each should be moving away from Earth due to the expansion of the universe, from fastest to slowest. a) 5 billion light-years b) 800 million light-years c) 2 billion light-years d) 70 million light-years e) 230 million light-years
Fastest a) 5 billion light-years c) 2 billion light-years b) 800 million light-years e) 230 million light-years d) 70 million light-years Slowest (Hubble's law tells us that the more distant a galaxy is from Earth, the faster it is moving away from us.)
Hubble's law is a relationship between galaxy speeds and galaxy distances. This relationship can be shown as a line on a graph of speed versus distance. Each of the following four graphs shows a possible relationship expressing Hubble's law. Rank the graphs based on their predictions of the speed, from fastest to slowest, for a galaxy located 400 million light-years away from Earth. a) Speed away from Earth (km/s) 12,000, Distance from Earth (millions of light-years) 1,200 b) Speed away from Earth (km/s) 30,000, Distance from Earth (millions of light-years) 600 c) Speed away from Earth (km/s) 20,000, Distance from Earth (millions of light-years) 1,000 d) Speed away from Earth (km/s) 30,000, Distance from Earth (millions of light-years) 400
Fastest d) Speed away from Earth (km/s) 30,000, Distance from Earth (millions of light-years) 400 b) Speed away from Earth (km/s) 30,000, Distance from Earth (millions of light-years) 600 c) Speed away from Earth (km/s) 20,000, Distance from Earth (millions of light-years) 1,000 a) Speed away from Earth (km/s) 12,000, Distance from Earth (millions of light-years) 1,200 Slowest (If you look at the speed corresponding to a distance of 400 million light-years on each graph, you will see that the speed declines in the order shown. Note also that this ranking puts the graphs in order of declining steepness. In other words, a steeper slope for Hubble's law would predict faster speeds for galaxies at particular distances.)
The following figures give the approximate speeds at which five galaxies are moving away from Earth due to the expansion of the universe. Rank the galaxies based on the amount of redshift that would be observed in each galaxy's spectrum, from largest to smallest. a) 130,000 km/s b) 45,000 km/s c) 18,730 km/s d) 5,264 km/s e) 1,577 km/s
Largest redshift e) 130,000 km/s b) 45,000 km/s a) 18,730 km/s c) 5,264 km/s d) 1,577 km/s Smallest redshift (Recall that a redshift tells us that an object is moving away from us, and the larger the redshift, the higher the speed. Note that expansion applies to the whole universe, so astronomers tend to think of galaxies being carried along with the expansion rather than moving "through" the universe. For this reason, redshifts due to expansion are often called "cosmological redshifts.")
The extreme luminosities of active galactic nuclei, the rapid internal motions found within the nuclei, and the associated jets of outflowing material all point to central supermassive black holes as the key powering agents of active galaxies. The different types of active galaxies, such as Seyferts, radio galaxies, and quasars, are all thought to be powered by this same mechanism. Part A The nucleus of an active galaxy contains several components, as shown in the figure below. The nucleus of an active galaxy contains several components, as shown in the figure below. Drag the appropriate labels to their respective targets. Note that not all labels will be used. a) Supermassive black hole b) Jets of high-speed particles c) Densely clustered star d) Magnetic field lines e) Accretion disk
Letters on the Diagram: A. (b) Jets of high-speed particles B. (d) Magnetic field lines C. (e) Accretion disk D. (a) Supermassive black hole (The engines of active galaxies are dominated by the supermassive black holes that dwell in the centers of these galaxies. The intense gravitational field of the black hole pulls material toward the center, where it accumulates into a swirling accretion disk. Collisions between particles in the accretion disk cause the material to heat up to high temperatures. As the material loses energy through radiation, it spirals inward toward the central black hole. Some of the material is lost in the form of high-speed jets that are confined by twisted magnetic fields. The jets and associated magnetic fields extend away from the active nucleus in a direction that is perpendicular to the accretion disk.)
Since the time of Hubble, astronomers have learned that the blue color observed in some galaxies is the result of recent star formation. The blue regions can be seen in the following figure, where the color differences are schematically depicted. This interpretation has been confirmed by multi-wavelength observations that have revealed the presence of star-forming gas clouds in galaxies hosting newly formed O-and B-type stars. (Sort the galaxy types according to their level of star-forming activity.) The figure shows a row of labeled images. First, there are four images of dotted forms with white centers. From left to right they are: circle, oval, more stretched oval, circle with smaller center, labeled as E0, E4, E7, S0, respectively. To the right from S0, the row separates in two branches of spiral form images. Top branch includes a form with bright arms close to each other, a form with more widespread bright arms, and a form with dark-toned arms spread even further and smaller light in the center. They are labeled as Sa, Sb, Sc, respectively. Bottom branch includes a form with bright arms and big light center, a form with more widespread bright arms, and a form with almost straightened up bright arms spread even further. They are labeled as SBa, SBb, SBc, respectively. All arms are shorter in this branch compared to the top one. Additionally, a light blot of irregular form is depicted, labeled as Irr. a) Barred-Spiral b) Elliptical c) Spiral d) Irregular
Little star-forming activity b) Elliptical Significant star-forming activity a) Barred-Spiral c) Spiral d) Irregular (Multi-wavelength observations of the gas and dust in different types of galaxies show a strong correlation between the amounts of cool gas and dust and the levels of star-forming activity as inferred from the visual appearances of the galaxies. Spiral, barred-spiral, and some irregular galaxies contain star-forming clouds along with blue regions of recently formed hot stars. By contrast, the elliptical galaxies no longer have these features. These smoother- and redder-appearing galaxies ceased forming stars a long time ago. The images below show examples of star-forming galaxies.)
A quasar consumes 1 solar mass of material per year, converting 15 percent of it directly into energy. Part A What is the quasar's luminosity, in solar units? Express your answer using two significant figures.
Mass of sun = 2×10^30 kg So energy produced per year = mc^2 x efficiency E = 2x10^30 x (3x10^8)^2 x 0.15 E = 2.7x10^46 Luminosity = E/ time in seconds L = 2.7x10^46/31556900 L = E/(365x3600x24) L= 8.5 x 10^38 Watt One solar luminosity = 3.846×10^26 W So L = 8.5 x 10^38 W/3.846×10^26 W/Sol luminosity So L = 2.2 x 10^12 solar luminosity
The following four graphs are the same as those from Part D, with each showing a possible relationship for Hubble's law. Rank the graphs based on the prediction they each would make for the current age of the universe, from oldest to youngest. a) Speed away from Earth (km/s) 30,000, Distance from Earth (millions of light-years) 400 b) Speed away from Earth (km/s) 12,000, Distance from Earth (millions of light-years) 1,200 c) Speed away from Earth (km/s) 30,000, Distance from Earth (millions of light-years) 600 d) Speed away from Earth (km/s) 20,000, Distance from Earth (millions of light-years) 1,000
Oldest universe b) Speed away from Earth (km/s) 12,000, Distance from Earth (millions of light-years) 1,200 d) Speed away from Earth (km/s) 20,000, Distance from Earth (millions of light-years) 1,000 c) Speed away from Earth (km/s) 30,000, Distance from Earth (millions of light-years) 600 a) Speed away from Earth (km/s) 30,000, Distance from Earth (millions of light-years) 400 Youngest universe (From Part D, you know that a steeper graph of Hubble's law predicts a higher speed for galaxies at particular distances. Because galaxies all started out close together (early in the history of the universe), higher speeds would mean that they would have reached their current distances in less time — and less time means a younger universe. In other words, the steeper the graph for Hubble's law, the more rapid the rate of expansion (a higher value of Hubble's constant), and the more rapid the rate of expansion the younger the universe.)
Part B - Emission properties of the central engine The most successful model for explaining nuclear activity in galaxies involves a supermassive black hole that is gravitationally accreting matter from its surroundings. According to this model, different regions of the active galactic nucleus produce different types of radiation. Referring to the figure, match the region with the type of radiation being emitted. a) Infrared b) X-Ray c) None d) Radio
Region Radiation Being Emitted Dusty Donut a) Infrared Supermassive Black Hole c) None Accretion Disk b) X-Ray Magnetized Jet d) Radio (Different regions of an active galaxy's central engine radiate at characteristically different wavelengths. The supermassive black hole itself is invisible. The accretion disk emits radiation across the spectrum. The innermost parts of the accretion disk, being the hottest, produce abundant X-ray emission. The dusty donut surrounding the accretion disk absorbs much of the high-energy radiation, re-emitting it mainly in the form of infrared radiation because of its relatively lower temperature. The magnetized jet can radiate at all wavelengths, but it is most commonly detected at radio wavelengths. Not all active galaxies in the sky are favorably oriented so that we can observe all of the active components. Active galaxies seen from the side often display radio-emitting jets and strong infrared emission from the dusty donut. However, the dusty donut obscures the view of the accretion disk and its X-ray radiation. Conversely, active galaxies seen face-on often emit brilliant UV and X-ray light from the exposed accretion disk but show no evidence of jets because of the face-on orientation.)
How is the Hubble constant related to the age of the universe?
The reciprocal of Hubble's constant is related to the age of the universe, it tells us what the age of the universe would be if the expansion rate has remained constant over time.
radio galaxies
a galaxy that emits unusually large quantities of radio waves; thought to contain an active galactic nucleus powered by a supermassive black hole. may have enormous lobes, invisible to optical telescopes, perpendicular to the plane of the galaxy
The Hubble galaxy classification system is based on the four basic galaxy types—elliptical, spiral, barred-spiral, and irregular. As depicted in the Hubble tuning fork diagram, the different galaxy types form a sequence of decreasing central concentration, symmetry, and smoothness of structure. Edwin Hubble originally thought that galaxies evolved over cosmic time from the simple elliptical structures to the more ragged irregulars. As astronomers have learned more about these various types, they have concluded that the Hubble Sequence does not correspond to an evolutionary progression. Astronomers have since determined that unless galaxies interact with each other, most galaxies retain their original structures.
a) Elliptical b) Spiral c) Irregular d) Barred-Spiral (The Hubble galaxy classification system is based on the four basic galaxy types—elliptical, spiral, barred-spiral, and irregular. As depicted in the Hubble tuning fork diagram, the different galaxy types form a sequence of decreasing central concentration, symmetry, and smoothness of structure. Edwin Hubble originally thought that galaxies evolved over cosmic time from the simple elliptical structures to the more ragged irregulars. As astronomers have learned more about these various types, they have concluded that the Hubble Sequence does not correspond to an evolutionary progression. Astronomers have since determined that unless galaxies interact with each other, most galaxies retain their original structures.)
Stars in a galactic disk are a) mostly found in the space between spiral arms. b) older than stars in the halo. c) evenly distributed within and between spiral arms. d) mostly found in the spiral arms.
a) mostly found in the space between spiral arms.
The graph shows that galaxies with high speeds as measured from Earth are __________. a) moving away from Earth and are farther from Earth than galaxies with lower speeds b) moving toward Earth and are farther from Earth than galaxies with lower speeds c) moving away from Earth and are closer to Earth than galaxies with lower speeds d) moving toward Earth and are closer to Earth than galaxies with lower speeds
a) moving away from Earth and are farther from Earth than galaxies with lower speeds (This is the essence of Hubble's law: More distant galaxies are moving away from us faster.)
Which of the following galaxy types is the most numerous in our Local Group of galaxies? a) small ellipticals and irregulars b) giant ellipticals c) large spirals
a) small ellipticals and irregulars (The two dominant galaxies in our Group each have a host of small galaxies orbiting them.)
Galaxy distance and Doppler redshift are correlated for galaxies.What do we call that correlation? a) the Hubble "law" b) Wein's relation c) redshift-distance relationd) period-luminosity relation e) both a and c
a) the Hubble "law"
The age of the universe is related to the slope of the graph of Hubble's law, and current data put the age of the universe at about 14 billion years. Suppose that future observations showed that the slope of Hubble's law on the graph is actually steeper than that shown. In that case, the age of the universe would be _________ than 14 billion years because the universe is expanding ______ than current data suggest. (Each choice gives words to fill in the two blanks, separated by a slash.) a) younger / more rapidly b) younger / more slowly c) older / more rapidly d) older / more slowly
a) younger / more rapidly (A more steeply sloped line for Hubble's law would indicate faster speeds for galaxies at all distances, which would mean a faster rate of expansion. And a faster rate of expansion means it has taken less time since the Big Bang for the universe to reach its present size. In other words, a steeper slope (which means a larger value of Hubble's constant) means a younger and more rapidly expanding universe.)
Imagine that when we looked out into the universe we found that the light from all galaxies was blueshifted (rather than redshifted) and that the light from the most distant galaxies was blueshifted by the greatest amount. Which statement best describes what we would conclude about the motions of galaxies in this case? a) All are moving toward Earth, with nearby galaxies moving faster than distant galaxies. b) All are moving toward Earth, with distant galaxies moving faster than nearby galaxies. c) All are moving away from Earth, with nearby galaxies moving faster than distant galaxies. d) All are moving away from Earth, with distant galaxies moving faster than nearby galaxies.
b) All are moving toward Earth, with distant galaxies moving faster than nearby galaxies. (In this hypothetical case, all the galaxies would be rushing toward Earth, with the more distant galaxies approaching at the fastest pace. This would tell us we lived in a collapsing universe rather than an expanding one.)
Hubble took spectra of galaxies in the 1930s. What did he find? a) All the galaxies showed blue line shifts. b) Most galaxies showed redshifts. c) Galaxies showed about half redshifts and half blueshifts. d) Galaxies showed no line shifts at all. e) Some galaxies showed a redshift that changed into a blueshift at other times.
b) Most galaxies showed redshifts.
The irregular classification is in some ways a method of dealing with galaxies that are clearly not elliptical or spiral in shape. Select the properties associated with irregular galaxies. (Check all that apply.) a) They all have centrally concentrated starlight. b) They are typically smaller than spiral galaxies. c) They exhibit vigorous star-forming activity. d) They are rare. e) They have tightly wound spiral arms. f) Some show evidence for prior collision or close encounter with another galaxy.
b) They are typically smaller than spiral galaxies. c) They exhibit vigorous star-forming activity. f) Some show evidence for prior collision or close encounter with another galaxy. (Irregular galaxies are typically smaller than spiral or normal ellipticals, of irregular form, and without spiral arms. Irr I galaxies are often characterized by lots of gas, dust, and associated star formation. Irr II galaxies have forms that indicate prior collisions or close encounters with other galaxies. Irregular galaxies are one of the most common types of galaxies.)
Not only does the central engine of active galaxies and quasars require a black hole, but ________ is also needed to provide the energy radiated. a) a collision with another galaxy b) an accretion disk of matter c) a very strong magnetic field d) a source of very high energy electrons e) a high rate of rotation of the black hole
b) an accretion disk of matter
Within 30 Mpc of the Sun, there are about a) few million galaxies. b) few thousand galaxies. c) 3 galaxies. d) 30 galaxies.
b) few thousand galaxies.
How would we get distances to the nearest galaxies (a few Mpc)? a) trig parallax b) period-luminosity relation for Cepheids c) Hubble's law (V = Hr) d) radar reflectione) main sequence fitting
b) period-luminosity relation for Cepheids
If the light from a galaxy fluctuates in brightness very rapidly, the region producing the radiation must be a) very hot. b) very small. c) rotating very rapidly. d) very large.
b) very small
By looking at the graph, what can we say about the galaxies that have the lowest speeds? a) They are moving away from Earth and are farther from Earth than galaxies with high speeds. b) They are moving toward Earth and are farther from Earth than galaxies with high speeds. c) They are moving away from Earth and are closer to Earth than galaxies with high speeds. d) They are moving toward Earth and are closer to Earth than galaxies with high speeds.
c) They are moving away from Earth and are closer to Earth than galaxies with high speeds. (This fact also follows from Hubble's law. Note that this applies to galaxies outside the Local Group. Within the Local Group, some galaxies move toward us, attracted by the gravity of the Milky Way.)
Which of the following is NOT one of the basic types of galaxy? a) spiral b) lenticular c) globular d) irregular e) elliptical
c) globular
Astronomers classify elliptical galaxies by a) the number of stars they contain. b) their colors. c) how flattened they appear. d) their diameters.
c) how flattened they appear.
Why do astronomers hypothesize that a massive black hole lies at the center of M87? a) Historical records show that a supermassive star at the center of M87 exploded as a supernova, leaving behind a black hole. b) Time-lapse images from space telescopes show stars falling to the center of M87 and then disappearing from view. c) Images of M87 made with powerful telescopes show a well-defined black region devoid of any stars. d) A very small region at the center of M87 releases an enormous amount of energy.
d) A very small region at the center of M87 releases an enormous amount of energy. (The video shows that no matter how much we zoom in, we still cannot resolve the bright source at the galactic center. The brightness of the source (and the fact that it is shooting out a jet of particles) tells us that it is releasing an enormous amount of energy. The fact that we cannot resolve its structure tells us that it is very small in size. Calculations show that the only way that such a small region can release so much energy is if its central power source is the infall of matter into a supermassive black hole.)
The third image in the video (with the most detailed view of the galactic center) is labeled "gas disk." Which of the following best describes what we are seeing in this photo? a) The bright central region is the bulge of the galaxy, and around it we see spiral arms. b) The bright central region is a place where many young stars are being born, and the surrounding material is the gas from which these stars are made. c) The black background in this photo is the supermassive black hole, and we see bright spots on top of it where nearby gas is emitting light. d) The black hole is located deep within the bright central region, and around this region we see gas that is orbiting the central black hole.
d) The black hole is located deep within the bright central region, and around this region we see gas that is orbiting the central black hole. (The bright center marks where most of the energy is coming from, and from Part A you already know that the energy source is thought to be a supermassive black hole. The immense gravity of the black hole causes surrounding gas (and stars) to orbit around it.)
Quasar spectra a) contain emission lines from unknown elements. b) look like the spectra of stars. c) show no spectral lines. d) are strongly redshifted.
d) are strongly redshifted.
Which type of galaxy can grow to the greatest mass and possess the largest number of globular clusters? a) spiral b) globular c) irregular d) elliptical e) lenticular
d) elliptical
According to "Galaxy Energy Spectra", active galaxies a) emit most of their energy at long wavelengths. b) emit very little energy at high frequencies. c) emit most of their energy in the visible part of the spectrum. d) emit large amounts of energy at all wavelengths.
d) emit large amounts of energy at all wavelengths.
Question 7Most of the galaxies (99%) are a) moving around randomly. b) showing Doppler blueshifts. c) moving in circles. d) rushing away from us. e) approaching us.
d) rushing away from us.
What do you need to know in order to estimate the distance of galaxies where we can no longer see individual stars/clusters/nebulae? a) trig parallax b) period-luminosity relation for Cepheids c) main sequence fitting d) supernovae give us a reasonable guess e) we cannot do it without V = Hr
d) supernovae give us a reasonable guess
Suppose that galaxy B is twice as far from Earth as galaxy A. Hubble's law predicts that galaxy B will be moving away from Earth with approximately _____. a) the same velocity as galaxy A b) four times the velocity of galaxy A c) half the velocity of galaxy A d) twice the velocity of galaxy A
d) twice the velocity of galaxy A (As the graph shows, Hubble's law (the straight-line fit to the data) predicts that a galaxy's recession velocity is proportional to its distance from Earth. Hubble's law therefore predicts that a galaxy twice as far away moves at twice the speed, a galaxy three times as far away moves at three times the speed, and so on.)
According to Hubble's law, with H0 = 70 km/s/Mpc, what is the recessional velocity of a galaxy at a distance of 180 Mpc? Express your answer using two significant figures.
70x180 = 12,600 v-rec = 1.3×10^4 km/s
If H0 = 85 km/s/Mpc? Express your answer using two significant figures.
85x180 = 15,300 v-rec = 1.5×10^4 km/s
What is an even larger galaxy cluster than the Virgo Cluster?
Abell 1689
A certain quasar has a redshift of 0.25 and an apparent magnitude of 13. Part A Using the data from Table 24.2 in the textbook, calculate the quasar's absolute magnitude. Express your answer using two significant figures.
As per the table, a redshift of 0.25 = 3300x10^6 ly (3300x10^6 ly)(0.25pc/1 ly) = 825000000 = 825x10^6 pc 13-(5log10((825x10^6 pc)/10 pc)) = -26.5822697427 M = -27
What allows the measurement of galaxies up to 25 Mpc away?
Cepheid variables
What forms the typical irregular galaxy?
Irr Type I - random shape (megallanic cloud) Type II - product of a shockwave explosion shape
What is the Hubble's tuning fork?
It is a tuning fork shaped diagram into which galaxies are organized morphologically - no true evolution of the galaxies in isolated galaxies Exclusions: gravitational pull, explosions, or collisions
What is a standard candle?
any object whose absolute magnitude is known and can be used to determine distance using their apparent magnitude - any object whose luminosity is known independently from its apparent brightness
Redshifted means that it is moving ________ from source and is ________.
away; positive
What are the qualities of a Seyfert galaxy?
changes the amount of radiation emitted up to twice every six months
Synchotron radiation produces a _______ spectrum
continuous non-thermal
_______ galaxies may bridge the gap between spiral galaxies and quasars. a) Hickson b) Arp c) Core-halo d) Seyfert e) Hubble
d) Seyfert
If the galaxy in Figure 24.11 ("Galaxy Rotation") in the textbook were smaller and spinning more slowly, then, in order to represent it correctly, the figure should be redrawn to show a) greater blueshift. b) greater redshift. c) larger combined amplitude. d) narrower combined line.
d) narrower combined line.
You see a distant (main-sequence!) B-type star like Rigel in a rather distant galaxy. What two things do you need to know in order to estimate its distance? a) how fast it is moving toward or away from youb) the apparent brightness (flux or apparent magnitude) c) the intrinsic brightness of main-sequence B-type stars like Rigel d) a and b e) b and c
e) b and c
You see a distant car in the night. What two things must you know in order to estimate its distance? a) how fast it is moving toward or away from you (Doppler shift) b) the apparent brightness (flux) of the distant headlights c) the intrinsic brightness of the headlights (e.g., 500 or 1000 watts) d) a and b e) b and c
e) b and c
Elliptical galaxies are filled with what types of stars?
old, red giants or white dwarfs
What does an active galaxy look like?
star-formation rings surrounding a very luminous core
What are the three types of non-stellar active galaxies?
Seyfert galaxies, radio galaxies, and quasars
The Milky Way Galaxy belongs to the
Local Group
According to Hubble's law, with H0= 70 km/s/Mpc, how long will it take for the distance from the Milky Way Galaxy of the Virgo Cluster to double?
((16.5 Mpc)(3.08x10^19 km/1 Mpc)) = 5.1x10^20 km ((70 km/s Mpc)(16.5 Mpc)) = 1155 km/s ((5.1x10^20 km)/1155 km/s) = 4.4155844 s Accepted my answer Computer's Correct Answer = 3.1x10^17
Match the words in the left-hand column to the appropriate blank in the sentences in the right-hand column. Use each word only once. 1. Our entire solar system orbits around the center of the ________ about once every 230 million years. 2. The Milky Way and Andromeda galaxies are among a few dozen galaxies that make up our ________. 3. The Sun appears to rise and set in our sky because Earth ________ once each day. 4. You are one year older each time Earth ________ about the Sun. 5. On average, galaxies are getting farther apart with time, which is why we say our ________ is expanding. 6. Our ________ is moving toward the star Vega at about 70,000 km/hr.
1. Milky Way 2. Local Group 3. rotates 4. orbits 5. universe 6. solar system
Part E How does this answer change if H0 = 55 km/s/Mpc ? Express your answer using two significant figures.
4,000/55 = 72.7272727 D = 73 Mpc
How many galaxies are within 1 Mpc?
50 galaxies that are gravitationally bound together
A certain quasar has a redshift of 0.25 and an apparent magnitude of 13. Part C Compare the apparent brightness of the quasar, viewed from a distance of 10 pc, with that of the Sun as seen from Earth.
F=L/4πd^2 (21.04x(10^38))/4π(10(3.08x(10^16))^2 = 1.5883174x10^72 apparent brightness of a quasar/apparent brightness of the Sun 1.5883174x(10^72)/1.4x(10^3) = 1.1345125x10^75 The apparent brightness of a quasar is 1.1x10^75 times greater than the apparent brightness of the Sun.
What methods are used to measure the galaxy?
Radar ranging to about 1 pc Stellar Parallax to about 200 pc Spectroscopic Parallax to about 10,000 pc Variable Cycle Stars to about 25 Mpc Tully-Fisher to about 200 Mpc Standard Candles to about 1 Gpc
A supernova of luminosity 1 billion times the luminosity of the Sun is used as a standard candle to measure the distance to a faraway galaxy. From Earth, the supernova appears as bright as the Sun would appear from a distance of 15 kpc . What is the distance to the galaxy?
Steps 1) 15 kpc = 15,000 pc 2) √(10^9x(3.828x10^26)/(3.828x10^26)) = 3.16x10^4 3) (15,000 pc)(3.16x10^4) = 474000000 4) 4.7 * 10^8
How does the rotation of a galaxy result in spectral line broadening? (Check all that apply.) a) The shifted lines from the two moving sides of the galaxy combine with the unshifted line from the center, resulting in a broader frequency distribution. b) Line widths from different elements are stretched at different rotation speeds. c) Light from opposite sides of the galaxy is shifted in different directions, causing the spectral lines to move to higher or lower frequencies relative to the unshifted line. d) The spectral lines from center, right, and left sides of the galaxy cancel out when adding.
a) The shifted lines from the two moving sides of the galaxy combine with the unshifted line from the center, resulting in a broader frequency distribution. c) Light from opposite sides of the galaxy is shifted in different directions, causing the spectral lines to move to higher or lower frequencies relative to the unshifted line.
Clouds of gas and dust as well as new star formation are typically seen in which of the following galaxy types? (Choose all that apply.) a) irregular b) elliptical c) spiral
a) irregular c) spiral (We usually see evidence of massive young stars and new star formation associated with clouds of gas and dust.)
Assuming that the bright core of M87 is powered by a supermassive black hole, which of the following best describes the source of energy that makes the core appear so bright? a) The black hole emits intense light as its huge mass is squeezed to infinite density at the black hole's singularity. b) Gravitational potential energy is converted to thermal energy as matter from the surrounding gas disk spirals into the central black hole. c) The immense gravitational force exerted by the central black hole in M87 triggers nearby stars to explode as supernovae. d) Gas and dust clouds form stars at a rapid rate due to forces from the central black hole in M87.
b) Gravitational potential energy is converted to thermal energy as matter from the surrounding gas disk spirals into the central black hole. (The black hole itself does not emit any light. Rather, the bright light comes from hot gas surrounding the black hole. This gas becomes hot in the process of falling toward the black hole because a large fraction (up to 40%) of its gravitational potential energy is converted into thermal energy (through friction in the disk) as it falls inward. Most of this energy is ultimately radiated away as light, explaining why the central region is so bright.)
