exam 4 study guide chapters 14, 15, 16, 18

The CMB is essentially uniform in all directions in the sky. This is an example of

isotropy

In every direction that astronomers look, they see the same Hubble's law, with the same slope. This is an example of

isotropy.

The observable universe is spherical because

light always travels at the same speed, in every direction.

The habitable zone is the place around a star where

liquid water can exist on the surface of a planet.

Extremophiles are organisms that

live in extreme conditions.

The distances to galaxies used to establish Hubble's law are found from:

standard candles, such as supernova.

The orbits of stars in the bulges of spiral galaxies most closely resembles the orbits of:

stars in an elliptical galaxy.

The CMB and the Big Bang theory are related because

the Big Bang theory predicted the existence of the CMB.

Based on what you have learned, which of the following measurements would we use to determine which galaxies are moving toward or away from the Milky Way?

the Doppler shift of spectral lines within the galaxy's spectrum

Scientists think that terrestrial life probably originated in Earth's oceans because

the earliest evidence for life on Earth comes in ocean-dwelling forms. energy was available there. all of the chemical pieces were there.

Each of the following images shows a type of galaxy. Identify each based on observed characteristics. (You may need to use the scrollbar under the Categories to view all of the choices.)

- barred spiral galaxy: central bar shape (looks round) - dwarf elliptical: small yellow dot - giant elliptical: big yellow dot (like a sun) - unbarred spiral: more slanted looking than the barred spiral

Evidence of a supermassive black hole at the center of the Milky Way comes from

- direct observations of stars that orbit it. - X-rays from material that is falling in. - strong radio emission from the region of the accretion disk.

Galaxies can appear differently depending on their orientation to our line of sight. For spiral galaxies, this is analogous to the figure showing coins tossed into the air. All the coins are round, but only face-on coins appear as such. Edge-on coins appear thin and flat, while the others appear as something in between. Given this concept, order the galaxies from most edge-on to most face-on. Assume that all the galaxies are perfectly round disks, like the coins.

- most edge on: green flat spiral, orange red spiral where you can see the circle in the middle, blue on the edge and yellow in the middle spiral, green, blue, yellow, brown, red (multicolor) that looks like its face on but is slanted - most face on: the only one that is centered, and is not slanted one bit

Supermassive black holes

- occur in most, perhaps all, large galaxies. - are "fed" by disturbed gas when galaxies interact.

This figure represents Hubble's tuning fork, a way of classifying galaxies based on their physical appearance. Label the types of galaxies shown on the tuning fork.

--<==> (Hubble tuning fork) - on the long end (on the left): ellipticals - on the first edge on the left (<): S0 - Bottom of the middle (==): barred spirals - top of the middle (==): spirals - on the last edge on the right (>): irregulars

Based on their descriptions, identify various galaxies on the Hubble tuning fork diagram.

--<==> (Hubble tuning fork) - on the long end (on the left, small red/yellow dot): Prominent central bulge; spherical shape; old red stars - on the bottom side of the middle (==): Elongated bulge and disk; mix of old and young stars - on the end (right tip >): no arms or bulge, mostly young stars - on the top side of the middle (==): roundish central bulge and disk, mix of old and young stars

Based on their physical characteristics, place the given galaxies in the proper place on Hubble's tuning fork.

--<==> (Hubble tuning fork) - on the long end on the left: small red/yellow dot - on the edge on the right (>): faint cloud looking stuff - on the bottom of the middle (==): slanted spiral - on the top of the middle (==): central spiral

The fact that the universe is expanding suggests that in the past, it was smaller, perhaps even infinitely so (a singularity), and since then, it has grown to the size it is today. Some event at the beginning of the universe, the Big Bang, provided the initial energy for this expansion. How quickly it expanded after that point, and whether it will stop or turn around and collapse, depends partly on the amount of mass in the universe. We describe this with the average density of the universe, where density is ρ = M/V, or mass per unit volume of space (e.g., number of grams per cubic centimeter). Recall that the force of gravity exists between all objects with mass.Given what you know of gravity and the definition of the density of the universe above, which of the following statements are correct?

A higher density will cause the universe's expansion to slow more with time.

Which of the following pieces of evidence support(s) the theory that the Milky Way is a spiral galaxy?

A.The 21-cm radiation emitted from neutral hydrogen clouds shows the existence of spiral arms. B.Most stars in our galactic neighborhood share the same relative motion around the galactic center. D.Ongoing star formation occurs in clouds of gas and dust.

Using the graph, sort the organisms according to whether or not they need oxygen to survive.

Anaerobic (do not need oxygen) - cyanobacteria Aerobic (needs oxygen) - Arthropods - Reptiles - Vertebrates

Using the information in the graph, determine why the first forms of life on Earth would have been extremophiles.

Atmospheric oxygen levels were too low to be a useful source of energy.

The following image depicts the chemical evolution of the Milky Way through various stages. Match the descriptions of some of these stages to the appropriate location in the evolution.

Chronological Order: An interstellar medium with just hydrogen and helium A supernova ejecting elements into space A star undergoing nucleo-synthesis A chemically enriched interstellar medium

The following images are intended to depict the stellar "recycling" that takes place in the universe as the death of stars provide the raw materials necessary for the birth of other stars. Label the stages in this process.

Chronological Order: Star formation Stellar nucleo-synthesis Supernovae and stellar mass loss Interstellar medium

Study the distribution and ages of stars in the figure, and use your observations to determine which of the following statements are correct.

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

The following graph shows the expansion of the universe over time, plotted at different matter density parameters (ΩΩm). Label each line with the correct description of the universe's fate.

Graph: C (Red line)-This universe continues to get larger forever. B (Green Line)-This universe expands but reaches a more or less constant size. A (Blue Line) - This universe ends as a singularity.

Hubble's law and the Big Bang theory are related because

Hubble's law is an observation that led to the development of the Big Bang theory.

As revealed by the cosmic microwave background, which of the following are properties of the young universe? (Select all that apply.)

It was dense; It was uniform on large scales; It was hot.

Sort the following tools and techniques with the characteristics they helped discover: Black hole in the center

Kepler's laws applied to star motions

Sort the following tools and techniques with the characteristics they helped discover: Age

Main-sequence turnoff of globular clusters

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.

Which of the following statements are true of the Milky Way?

The Milky Way has globular clusters The Milky Way has two major arms The Milky Way is mostly dark matter.

Dark energy has been hypothesized to solve which problem?

The expansion of the universe is accelerating.

Our Milky Way Galaxy is a giant spiral galaxy. For this figure, label the various, basic parts of the galaxy and indicate the total diameter of the galaxy.

The galaxy extends 300,000 lys big glowy thing is the Galactic Halo small little dots: Globular Clusters little baby clouds: Magellan Clouds the galaxy itself: the Galactic Disk

We see distant galaxies that appear to be moving faster than the speed of light! This apparent paradox comes about because the shifts in wavelength we observe owing to the expansion of the universe are not actually caused by the Doppler shift of light from a moving source, but rather by something else entirely. The following figure demonstrates this effect: as light travels through expanding space, the space between its crests (or peaks) is also expanding. How will this affect light according to how long it has been traveling through this expanding space?

The longer the light has been traveling, the more strongly redshifted it will be.

The following figure shows the estimated relative amounts of water on the moons Europa and Titan and on Earth. These moons in our Solar System likely have more liquid water than all the oceans on Earth. How can this be true when the moons are so much smaller than Earth?

The oceans on these moons are likely much deeper than Earth's.

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.

What can we infer from the fact that nearly all galaxies are moving away from us?

The universe is expanding.

in the following figure, why does ant A see paper clip E receding from it the fastest? (Pic: shows rainbow colored paperclips representing time in 3 rows, with each ant going across three rows)

There is more space to stretch between them.

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.

How would the light we observe on Earth from a high-redshift galaxy compare to the light observed from a low-redshift galaxy?

We will see the high-redshift galaxy as it was earlier in time than the low-redshift galaxy.

The "edge" of the observable universe is

a consequence of the fact that light travels at a finite speed.

Parallel universes are

a hypothesis.

The following image shows a few stars' orbits around the innermost 0.03 parsecs of the galactic center. Their extreme orbital speeds indicate they are orbiting an object with 4 million solar masses. Considering the following objects and their properties, which is most likely to exist at the very center of our galaxy?

a supermassive black hole

In general, older stars have lower __________ than younger stars.

abundance of heavy elements

We appear to be at the center of the observable universe because

all the light from all directions has had the same amount of time to get here.

The Urey-Miller experiment produced ______ in a laboratory jar.

amino acids

When they look into the universe, astronomers observe that nearly all galaxies are moving away from the Milky Way. This observation suggests that

an observer in a distant galaxy would make the same observation.

All the light in an AGN outburst travels

at the same speed.

All the light in an AGN outburst is emitted

at the same time.

In the Hubble scheme for classifying galaxies, what type of galaxy is the Milky Way?

barred spiral

The actual universe is likely __________ the observable universe.

bigger than

How do astronomers detect dark matter?

by comparing luminous mass to gravitational mass

The cosmological constant accounts for the effects of

dark energy.

Which of the following contributes the largest percentage of total mass of a spiral galaxy?

dark matter

If astronomers were to ignore any cosmological constant, the future of the universe could be determined solely from the

density of the universe.

Hubble's law was discovered using measurements of two properties of a galaxy: _______ and _______.

distance; recession velocity

Where in the universe did the Big Bang take place?

everywhere in the universe

Determine if the following statement is true, false, or neither:If a galaxy's redshift measured from Earth implies that it is moving 8,000 km/s away from us owing to the expansion of the universe, an observer in every other galaxy in the universe will also measure a redshift for that galaxy corresponding to a velocity of 8,000 km/s.

false

Identify the two problems of cosmology that are solved by inflation.

flatness; horizon

There are many different methods of determining the distances of remote objects. Each method works best for a certain range of distances. Label the figure with the proper method of finding distances for each class of objects.

from left to right (small to big) - solar system: radar - nearby stars: parallax - Milky Way: spectroscopic parallax - nearby galaxies: cepheid variable stars - distant galaxies: type 1a supernovae

Astronomers observe two galaxies, A and B. Galaxy A has a recession velocity of 2,500 km/s, while galaxy B has a recession velocity of 5,000 km/s. This means that

galaxy B is twice as far away as galaxy A.

Which property is detectable for both dark matter and the supermassive black hole at the center of the Milky Way?

gravity

The orbits of stars in elliptical galaxies:

have random orientations.

Cosmic rays are

high-energy particles.

In astronomy, isotropy means that the universe is the same __________, and homogeneity means that the universe is the same __________.

in all directions; in all locations

The following NASA image shows the Whirlpool galaxy. Identify the parts of the galaxy by dragging them to the appropriate target.

in the center: Central Bulge on the outside curved bit: Spiral Arm

Where are the youngest stars in the Milky Way Galaxy?

in the disk

In the phrase "theory of evolution," the word theory means that evolution

is a well-tested, well-corroborated scientific explanation of natural phenomena.

The best evidence for dark matter in the Milky Way comes from the observation that the rotation curve

is quite flat at great distances from the center.

Which location best represents the location of the Sun in the Milky Way Galaxy?

middle of spiral arm, orion arm

In general, the Milky Way has:

more abundant heavy elements as time passes.

Astronomers know that dark matter is present in galactic halos because the speeds of orbiting stars _________ far from the center of the galaxy.

remain about constant

Galaxies are classified according to their

shape

What types of stars indicate recent star formation in a region?

short-lived, hot, massive stars, like O- and B-type stars

Currently, star formation rates are highest in

spiral galaxies

The size of the Milky Way is determined from studying __________________ in globular clusters.

standard candles

Detailed observations of the structure of the Milky Way are difficult because

the Solar System is embedded in the dust and gas of the disk.

The light that comes to us from active galactic nuclei comes from a volume about the size of

the Solar System.

Looking toward the galactic center, we see no redshift or blueshift. This tells us:

the Sun and the center are not moving toward or away from each other.

All life on Earth must eventually come to an end because

the Sun will make the planet uninhabitable.

In spiral galaxies, stars form predominantly in:

the arms of the disk.

The cosmic microwave background looks like the spectrum of a blackbody at the low temperature of 2.73 K because:

the light has been redshifted since the Big Bang.

The cosmological redshift in Hubble's law is distinct from the redshift arising from the Doppler effect because:

the redshift happens as the photon moves through expanding space.

The length of time that it takes for the light from the outburst to pass the observer indicates

the size of the AGN.

Older stars are found farther from the midplane of a galactic disk because

the stars have lived long enough to move there.

Astronomers will never directly observe the first few minutes of the universe because

the universe was opaque at the time.

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

Globular clusters are important to understanding the Milky Way because

they reveal the size of the Milky Way and Earth's location in it.

If the main-sequence turnoff of a star cluster occurs near the very top of the main sequence, then the cluster is

very young.

The vast majority of antimatter in the early universe

was annihilated with matter.

As shown in the two images, the stars in a spiral galaxy either orbit irregularly in all directions or together in one direction. Match each stellar orbit to the correct location in a spiral galaxy.

- Bulge of spiral galaxy: arrows going in every direction - Disk of spiral galaxy: arrows going the same exact direction

Which of the following statements regarding the expansion of the universe are correct?

- More distant galaxies appear to be moving more quickly away from any particular galaxy than those that are closer to that galaxy. - From the vantage point of each galaxy, most other galaxies will appear to be moving away.

As applied to the universe, what is the meaning of critical density?

Above this density, the universe will eventually collapse.

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?

B. Observe it in the infrared.

According to the figures, what is true about how ant A and ant E observe each other? (Pic: shows rainbow colored paperclips representing universe A and universe E, the ants are moving towards each other)

Both ants see the other moving away at the same speed.

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. Think about what you have learned about stars and galaxies so far, and determine which of the following statements is correct.

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.

Sort the following tools and techniques with the characteristics they helped discover: Rotation curve

Doppler shift of 21-cm line in H II clouds

Sort the following tools and techniques with the characteristics they helped discover: Size

Globular clusters as standard candles

Why is the Milky Way Galaxy not expanding together with the rest of the universe?

Local gravity dominates over the expansion of the universe.

Sort the following tools and techniques with the characteristics they helped discover: High star formation

Spectral analysis of star atmospheres