Astronomy Final: 15 and 16

Which of the following is not evidence of spiral arms in the Milky Way

Which of the following is not evidence of spiral arms in the Milky Way

Spiral Arm Tracers

star formation, hot main sequence stars, OB association

Using star counts, William and Caroline Herschel concluded that

the Milky Way Galaxy is disk-shaped

Show how this affects the appearance of a galaxy by dragging labels to the following images in order from most edge on to most face on. Assume all of the galaxies are actually perfectly round in shape and that any apparent elongation is due purely to their orientation.

#24 a,b,d,e,f,c

Which of the following observations support the idea that the only place in the Milky Way where active star formation is occurring today is in the spiral arms?

-Spiral arms in the Milky Way's disk are traced out by higher gas density, OB associations, and open clusters. -OB associations consist of very hot stars with extremely short lifetimes. -Globular clusters contain no gas and have no high-mass stars. -The halo of the Milky Way has almost no gas or dust.

Galaxy A is receding from us at x km/s, while galaxy B's recession velocity is 3x km/s. Based on Hubble's law, which statement is true?

A is 1/3 as far from us as B.

A galaxy is observed moving away from ours at 12535 km/s. What is its distance from us, in megaparsecs?

Assume a Hubble's constant value of 69 km/s/Mpc. 181.67Mpc

Which of the following cosmic distance ladder methods uses cyclical changes in a star's brightness over time to determine distance?

Cepheid variables

When removing the effects of orientation, galaxies also have intrinsically different shapes that make them appear different from one another. Edwin Hubble classified galaxies based on these shapes, as shown in the following "tuning fork" diagram. Based on Hubble's tuning fork diagram, match the type of galaxy to its description.

E0- smooth basketball-shaped bulge with no spiral arms Sc- relatively small bulge surrounded by open, knotty spiral arms Sa- relatively large central bulge surrounded by tight, smooth spiral arms E5- smooth american football-shaped bulge with no spiral arms

Study the distribution and ages of stars in the figure, and use your observations

Globular clusters formed before the gas from which our galaxy formed had time to collapse into a disk and The cloud of gas from which our galaxy formed was originally spheroidal in shape

A galaxy has been determined to be 68 Mpc from us. At what velocity, in kilometers per second, is it receding

Hubble's constant value of 69 km/s/Mpc so 4692 km/s

Which of the following galaxy types is most likely to be clearly identifiable, regardless of orientation?

Irr

What role did interstellar dust play in the quest to determine the shape and size of our galaxy

It obscured some regions and made others appear dimmer and redder

If you compare the processes of star formation and spiral galaxy formation, you may have noticed that they share some similarities. Even though galaxy formation occurs on size scales several billion times larger in volume (and mass), the laws of physics governing it are the same ones governing star formation. Which of the following characteristics do the processes of star formation and spiral galaxy formation not have in common?

Most of the mass driving the self-collapse is dark matter with some gas

The orbital properties of the stars within the innermost 0.03 parsecs of the galactic center, as plotted in the following diagram, indicate that there are 4 million solar masses within the tiny, central region. What do these observations likely imply about the very center of our galaxy

Most of the mass in the center of our galaxy is invisible

The color of a galaxy is a combination of the light from all its stars, which can possibly span all spectral types (temperatures). This image of a spiral galaxy demonstrates a distinct difference in color between the galaxy's central bulge and its outer spiral-armed disk. On the basis of the colors and lifetimes of different types of stars, which of the following statements best describes the current state of the bulge and disk?

New stars are forming mostly in the disk.

What is at the very center of our galaxy? This question is difficult to answer because the center is completely obscured to our eyes behind a large amount of dust. On the basis of what you know about dust from previous chapters, what can be done to improve our view of the galaxy's center?

Observe it in the infrared

The age of the Milky Way Galaxy is about 13 billion years, but our Solar System is less than 5 billion years old. If the Sun had been one of the very first stars, how would the Sun and its evolution differ

The Sun would have lower metallicity

How did dust affect Shapley's RR Lyrae measurements

The apparent brightnesses were fainter than they would be if there were no dust

Label the parts of the Milky Way Galaxy

The bulge is the central spheroid of stars in a spiral galaxy. Then there is the thin, round disk with the spiral pattern in it. Surrounding both is the thin, diffuse halo containing stars and dark matter. The Sun happens to be about halfway out from the center of the galaxy.

Given that Shapley calculated the size of the Milky Way based on the stars' apparent brightness, how did not including the effects of gas and dust affect Shapley's calculation

The distance calculated to each globular cluster was too large, and thus his size for the Milky Way was too large

Based purely on your observations of this plot, which of the following statements best describes the visible distribution of mass within that galaxy?

The highest concentration of mass is in the center of the galaxy, and it decreases with increasing distance from the center. #23

Which statement(s) about galaxy groups is/are true? -Interactions between massive and less-massive galaxies affect only the smaller galaxies. -Galaxy mergers are rare in galactic evolution. -Galaxies in a group are all moving away from each other. -The largest galaxies tend to have satellite galaxies. -Tidal streams can result from galaxy interactions.

The largest galaxies tend to have satellite galaxies. Tidal streams can result from galaxy interactions.

The bottom two graphs are rotation curves, which show how fast objects within a galaxy are orbiting as a function of their distance from the center. The center graph is the predicted orbital velocity we would expect based on how much mass we see from stars and gas. The bottom graph is the observed velocity

The observations show higher velocities than is predicted, mostly in the outer regions of the galaxy, indicating that there is more mass in the outer regions than we can see

Given that elliptical galaxies are relatively round, ranging in shape from spheres to more squished spheroids similar to an American football, which of the following statements most accurately describes the orbits of stars in an elliptical galaxy

The stars all have irregular orbits in all directions about the center

We have seen that the disks of spiral galaxies contain stars that move in circles in the same direction around the central bulge. The disks contain many bright blue stars that have formed recently, giving them their distinct colors. The disks also often contain bright spiral-shaped arms with darker regions in between. On the basis of your observations of the video, which of the following most accurately describes the spiral arms?

The stars move in and out of the arms while they rotate around the galaxy center.

The nearly edge-on view of the spiral galaxy shown gives us some clues as to why the level of recent star formation is different between bulges and disks. Consider the type of environment in which new stars form, and use your observations of the picture to choose the statement that best describes why there is more star formation in the disk

There is more cold, dense gas in the disk than in the bulge

The relative motion of stars with respect to the spiral arms suggests that the arms are not made out of stars, despite their appearance. Rather, they are spiral density waves of energy that move through the galaxy, compressing gas within the peaks of the waves. Of the two images, this is especially visible in the image at right.What effect would you expect this to have on stars

There will be more star formation inside the spiral arms

Which of the following is not evidence that it is a supermassive black hole that powers active galactic nuclei?

We see a small dark spot at the base of the jets seen coming from some active galaxies.

Which of the following objects is most likely to exist at the very center of our galaxy, considering your knowledge of the properties of these objects

a supermassive black hole

Population I

believed to be younger stars, located mostly in galactic disk, almost all hot blue stars

Where is the Sun located in this view

below the light- the Sun is located 8 kiloparsecs (kpc) from the center of the Milky Way or slightly more than halfway out from the center to the edge

(1) blazars, which are radio-loud (meaning bright in radio waves) extremely compact quasars; (2) Type I Seyfert galaxies, which show the broadest emission lines, indicating fast-moving gas; (3) Type II Seyfert galaxies show only narrower emission lines, indicating that the material is moving less rapidly.

c,a,b

Astronomers determined that elliptical galaxies have dark matter by

calculating that the average stellar orbital velocity is greater than the expected escape velocity based on the luminous matter.

Galaxies are typically classified based on their "morphology" or appearance. This tradition goes back to Hubble, who classified galaxies as spirals, barred spirals, ellipticals, or irregulars. He further subdivided the spirals based on the tightness of the spiral pattern and the size of the central bulge (based on what he thought they would look like "face on"). To help visually present this classification scheme, he came up with what is today called the Hubble tuning-fork diagram. Select the galaxy images and place them in their proper locations on the tuning-fork diagram shown below.

check diagram

formation of a star and spiral galaxy in order, from earliest to latest

cloud like to clearest planet like

This interactive shows views of the Milky Way galaxy, the galaxy we reside in, from various angles. After examining these views, determine which of the following everyday objects best matches the shape of the Milky Way.

dinner plate

Which of the following structures is/are found in all spiral galaxies?

disk spiral arms bulge

A galaxy is observed to be spheroid and to have increasing stellar density toward the center. What is its galaxy classification?

elliptical

illustrate evidence for dark matter in the Milky Way Galaxy

evidence is the line graph of distance from galaxy center on x-axis and orbital velocity on y-axis

#16 diagram

galaxy 3,2,4,1 left to right of the line

Not Spiral Arm Tracers

globular cluster, cool main sequence stars

Outside the Spiral Arms

globular clusters dwarf galaxies bulge

With which of the four fundamental forces must dark matter interact?

gravity

Population II

have lower metallicity, located mostly outside galactic disk

If there were no dark matter, the orbital period of the Sun around the galactic center would be

longer- with no dark matter, there would be a smaller gravitational force acting on the Sun and holding it in its orbit around the galaxy. This would mean a lower velocity and a longer period.

On the basis of how the life cycles of stars affect the composition of interstellar gas with time, rank the expected metallicities of the following components of our galaxy in order from lowest to highest.

lowest- halo bulge thin disk -highest

Inside the Spiral Arms

open clusters the Sun OB associations

Which method of determining distance would be most appropriate for a ground-based observer trying to find accurate distances out to approximately 100 parsecs? (Choose the lowest applicable rung on the cosmic distance ladder.)

parallax

Compare two Milky Way disk stars, one 3 billion years old and one 5 billion years old. The younger one is more likely to

reach smaller heights as it oscillates above and below the disk

The unified model of AGNs

says that the orientation of the observer accounts for the differences among the types of AGNs.

Which of the following describe(s) characteristics of AGNs that point to a black hole as the central engine?

short timescales for variability in brightness, compact size of the core, relativistic velocity of jets

spiral, barred spiral, elliptical

spiral- any round and spiraling barred spiral- spirals but is not round elliptical- does not spiral but is on old star that round with dust around #15

Hubble's law says that

the more distant the galaxy is, the faster it appears to be receding from us.

The large number of stars in each cluster assures that each will contain many RR Lyrae stars. Like Cepheids, RR Lyrae stars are unstable in size and vary periodically in brightness, as shown in the top plot of the following image. More luminous RR Lyrae stars have longer periods between peaks in brightness, as shown by the bottom plot. To build a three-dimensional map of globular cluster distribution in the Milky Way, we need to determine each cluster's distance from us. Which of the following measurements would allow you to determine each cluster's distance from us?

the period and apparent brightness of RR Lyraes in each cluster

The following image shows that the central 5 parsecs of the Milky Way (marked toward the bottom of the image) are extremely dense, with hundreds of thousands of stars packed into this relatively small region. What property of these stars can we measure to determine how much mass is at the center of the galaxy

their velocities as they orbit the center

In the following diagram, the magnitudes and colors for a globular cluster are plotted in the H-R diagram below the cluster image. The top of the main-sequence line is the turnoff point, where all the stars brighter than that have run out of hydrogen in their cores and evolved off the main sequence. Based on the figure, estimate how old this cluster is.

10 billion years

Spiral arms are blue because they contain many bright, high-mass stars, which outshine the fainter red stars in that location. The space in between the arms lacks these blue stars but does have a large number of fainter red stars, as shown in the figure.

Both red and blue stars form inside the spiral arms. Then both stars begin to move out of the arms, but the blue stars die before they can get very far.