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Astro 18 > Module 12 > Flashcards

Module 12 Flashcards

1
Q

What does the Milky Way Galaxy look like?

A

It is a vast spiral galaxy holding more than 100 billion stars with a disk approximately 100,000 light-years in diameter and a central bulge surrounded by a dimmer halo.

The galaxy’s disk is about 1000 light-years thick, and most bright stars are found in the disk.

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2
Q

How do stars orbit in our galaxy?

A

Stars in the disk orbit in roughly circular paths, while halo stars have more random and less organized orbits.

The orbits also differ in thickness and velocity depending on the region of the galaxy.

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3
Q

What is galactic recycling?

A

It is the process by which matter cycles from stars into interstellar space and back into new stars, maintaining the galaxy’s ecosystem.

This process is essential for the birth of new stars and the evolution of life.

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4
Q

What do halo stars tell us about our galaxy’s history?

A

They provide insights into the formation and evolution of the Milky Way Galaxy.

Halo stars are older and can indicate past interactions and the galaxy’s growth.

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5
Q

How did our galaxy form?

A

The Milky Way formed from the gravitational collapse of gas and dust in the early universe, leading to the formation of stars and clusters.

This process involved complex interactions over billions of years.

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6
Q

What is the evidence for a black hole at our galaxy’s center?

A

Observations of stars orbiting rapidly around a massive, compact object suggest the presence of a supermassive black hole.

The mass of this black hole is estimated to be millions of times that of the Sun.

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7
Q

What are the characteristics of disk stars’ orbits?

A

Disk stars orbit the galactic center in circular paths, moving in the same direction and nearly the same plane, with periodic up-and-down motion.

This motion contributes to the thickness of the disk.

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8
Q

How do halo stars’ orbits differ from those of disk stars?

A

Halo stars have random orbital orientations and can swoop high above and below the disk, often moving at high velocities.

This results in less organized and puffier halo structures.

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9
Q

What is the shape of the Milky Way Galaxy?

A

It has a spiral shape with a central bulge and surrounding halo, resembling a flat disk with spiral arms.

The shape is difficult to discern from within the galaxy.

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10
Q

Fill in the blank: The Milky Way’s disk is filled with _______.

A

interstellar gas and dust.

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11
Q

True or False: The Milky Way is one of about 100 billion galaxies in the observable universe.

A

True.

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12
Q

What major role does interstellar medium play in our understanding of the Milky Way?

A

It obscures our view of the galaxy, leading to misconceptions about its size and shape until its effects were understood.

This understanding helped astronomers refine their models of the galaxy.

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13
Q

What did Harlow Shapley discover about the Milky Way?

A

He determined that globular clusters are centered on a point tens of thousands of light-years from the Sun, indicating the true center of the galaxy.

This finding contradicted earlier beliefs about the Sun’s position in the galaxy.

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14
Q

What is the role of the European Space Agency’s GAIA mission?

A

It has measured proper motions for over a billion stars, providing valuable data on their orbits and the structure of the Milky Way.

This mission enhances our understanding of stellar movements across the galaxy.

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15
Q

What is the angular rate of motion for a star that moves 1 arcsecond over 10 years?

A

0.1 arcsecond per year

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16
Q

What mission has measured proper motions for over a billion stars?

A

European Space Agency’s GAIA mission

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17
Q

What is the typical orbital speed of the Sun around the Milky Way?

A

About 220 kilometers per second

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18
Q

How long does it take the Sun to complete one orbit around the galactic center?

A

About 230 million years

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19
Q

What law allows us to determine the mass of a large object based on the orbital motion of a smaller object?

A

Newton’s version of Kepler’s third law

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20
Q

Why can we only calculate the mass within the Sun’s orbit using its orbital motion?

A

Net gravitational forces from mass outside the orbit cancel out

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21
Q

What is the total amount of mass within the Sun’s orbit around the Milky Way?

A

About 100 billion times the mass of the Sun

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22
Q

What does the orbital speed of distant stars in spiral galaxies suggest about the galaxy’s mass distribution?

A

Most of the mass resides far from the center and is distributed throughout the halo

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23
Q

What term is used to describe mass in the galaxy that does not emit detectable light?

A

Dark matter

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24
Q

What is the percentage of heavy elements in the galaxy’s gaseous content by mass?

A

About 2%

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25
What are the two lightest elements present in the early universe?
Hydrogen and helium
26
What is the star-gas-star cycle?
The process of stars forming from gas, shining, and returning material back to the interstellar medium
27
How do low-mass stars return mass to the interstellar medium?
Through stellar winds and planetary nebulae
28
What happens to high-mass stars at the end of their lives?
They explode as supernovae
29
How do supernovae affect the interstellar medium?
They create shock fronts that compress and heat surrounding gas
30
What phenomenon can cosmic rays generated by supernovae cause?
Genetic mutations in living organisms
31
What is a superbubble?
A large cavity of hot gas formed by the overlap of multiple supernova explosions
32
What model describes the cycling of gas between the Milky Way's disk and halo?
Galactic fountain model
33
What is the primary component of the interstellar medium in the galaxy?
Hydrogen
34
Fill in the blank: The mass of the galaxy within a distance r from the center can be calculated using the _______.
Orbital velocity law
35
True or False: Sound can travel through the interstellar medium.
False
36
What is the galactic fountain model?
A model suggesting superbubbles and blowouts play a role in the galaxy-wide recycling system.
37
How do superbubbles affect the galactic disk according to the galactic fountain model?
They blow gas out of the galactic disk, which cools into gas clouds that rain back down.
38
What type of gas is primarily found in the Milky Way?
Atomic hydrogen gas.
39
What is the composition of atomic hydrogen gas in the Milky Way by mass?
* 71% hydrogen * 27% helium * 2% heavier elements
40
What spectral line is used to map the distribution of atomic hydrogen gas?
21 centimeters.
41
What is the estimated total amount of atomic hydrogen gas in the Milky Way?
About 5 billion solar masses.
42
What are the two forms of atomic hydrogen gas?
* Large, tenuous clouds of warm atomic hydrogen (10,000 K) * Smaller, denser clouds of cool atomic hydrogen (100 K)
43
How long can matter remain in the atomic hydrogen stage of the star-gas-star cycle?
For millions of years.
44
What is the role of magnetic fields in atomic hydrogen clouds?
They may provide support to clouds that gravity would otherwise cause to collapse.
45
What small component do clouds of atomic hydrogen contain?
Interstellar dust.
46
What happens to hydrogen atoms as the temperature drops in a cool cloud of atomic hydrogen?
They combine into molecules, primarily hydrogen molecules (H2).
47
What are molecular clouds and where are they found?
The coldest, densest collections of gas in the interstellar medium, often congregating into giant molecular clouds.
48
What is the estimated total mass of molecular clouds in the Milky Way?
About 5 billion solar masses.
49
What phenomenon occurs when stars form in a large molecular cloud?
A cluster of stars is born.
50
What effect do newly formed massive stars have on their surrounding molecular cloud?
Their radiation erodes the surrounding gas.
51
What is the ultimate fate of gas in the star-gas-star cycle?
Some gas becomes permanently locked away in brown dwarfs and stellar remnants.
52
What is the expected time frame for the cessation of star formation in the Milky Way?
About 50 billion years from now.
53
What do different states of interstellar gas indicate about the Milky Way?
Different regions are in various stages of the star-gas-star cycle.
54
What do the dark patches in the x-ray image of the Milky Way correspond to?
Bright regions of long-wavelength infrared emission from dust.
55
What are ionization nebulae?
Colorful, wispy blobs of glowing gas near hot stars, ionized by ultraviolet photons.
56
What causes the blue colors in reflection nebulae?
Starlight reflected from dust grains.
57
How do spiral arms of the galaxy relate to star formation?
They are home to molecular clouds and numerous clusters of young, bright, blue stars.
58
What evidence suggests that spiral arms are regions of active star formation?
Presence of hot blue stars, ionization nebulae, and enhanced amounts of molecular gas.
59
Do spiral arms move with the stars in the galaxy?
No, stars orbit at approximately the same speed.
60
What is the general shape and structure of the Milky Way Galaxy?
The Milky Way Galaxy is a spiral galaxy consisting of a thin disk, a central bulge, and a spherical halo surrounding the disk.
61
How do stars in the Milky Way travel in relation to their distance from the center?
Stars near the center travel in smaller circular orbits and complete their orbits more quickly than stars further out.
62
What phenomenon causes the spiral arms of galaxies to appear as they do?
The spiral arms are caused by disturbances called spiral density waves that propagate through the gaseous disk.
63
What is the impact of spiral density waves on star formation?
Spiral density waves cause gas clouds to pack more densely together, triggering the formation of new star clusters.
64
What are ionization nebulae also known as?
Ionization nebulae are also known as emission nebulae and H II regions.
65
What distinguishes halo stars from disk stars?
Halo stars have disorderly orbits, are generally very old, and contain smaller proportions of heavy elements compared to disk stars.
66
What is the typical age of halo stars?
Halo stars are generally at least 12 billion years old.
67
What is the composition of disk stars in terms of heavy elements?
Disk stars have heavy-element proportions near 2%, similar to that of our Sun.
68
What is the composition of halo stars in terms of heavy elements?
Halo stars can have heavy-element proportions as low as 0.02%.
69
Why can't new stars form in the halo of the Milky Way?
The halo does not contain the cold, dense molecular clouds required for star formation.
70
What is the primary model for the formation of the Milky Way Galaxy?
The galaxy formed from a giant protogalactic cloud of hydrogen and helium gas, along with dark matter.
71
What role does gravity play in the formation of the Milky Way?
Gravity caused the protogalactic cloud to contract and fragment, leading to the formation of stars.
72
What does the law of conservation of angular momentum explain about the Milky Way's disk?
It explains how the remaining gas settled into a flattened, spinning disk.
73
What is the evidence for a black hole at the center of the Milky Way?
Stars near the center exhibit orbits indicating a massive object, inferred to be a black hole of about 4 million solar masses.
74
What is Sagittarius A*?
Sagittarius A* (Sgr A*) is a source of radio emission at the center of the Milky Way, associated with the black hole.
75
What unusual behavior has been observed from Sgr A*?
Sgr A* exhibits relatively faint x-ray emissions, with occasional large x-ray flares.
76
What might cause the x-ray flares observed from Sgr A*?
They may be caused by energy released from comet-size lumps of matter being torn apart by the black hole's tidal forces.
77
What is the significance of the Milky Way's stellar winds and explosions?
They mix new heavy elements into the gas of the Milky Way, contributing to the recycling of materials for new stars.
78
How does the Milky Way Galaxy function as a 'recycling plant'?
It converts gas expelled from each generation of stars into the next generation, allowing heavy elements to solidify into planets.
79
What type of galaxy is the Milky Way?
Spiral galaxy ## Footnote The Milky Way Galaxy has a thin disk, central bulge, and spherical halo.
80
What is the diameter of the Milky Way Galaxy?
About 100,000 light-years ## Footnote This measurement refers to the diameter of the thin disk.
81
What does the disk of the Milky Way contain?
Interstellar medium of gas and dust ## Footnote The halo contains only a small amount of hot gas and virtually no cold gas.
82
How do stars in the disk of the Milky Way orbit?
In about the same plane and in the same direction ## Footnote Halo stars have orbits that are randomly inclined to the disk.
83
What is the significance of the orbital motions of stars in the Milky Way?
They allow us to determine the distribution of mass in our galaxy ## Footnote This includes understanding the different types of star orbits.
84
How is gas recycled in the Milky Way?
Through the star-gas-star cycle ## Footnote Stars form from gas clumps, explode as supernovae, and their gas contributes to new star formation.
85
Where do stars tend to form in the Milky Way?
In spiral arms ## Footnote These regions are characterized by the presence of hot, massive stars and ionization nebulae.
86
What do halo stars tell us about the Milky Way's history?
They are old, low-mass stars with a smaller proportion of heavy elements ## Footnote This indicates they formed early in the galaxy's history.
87
How did the Milky Way form?
From the collapse of protogalactic clouds of hydrogen and helium gas ## Footnote This process led to the formation of a spinning disk around the galactic center.
88
What evidence suggests a black hole exists at the center of the Milky Way?
Orbits of stars near the center indicate a black hole about 4 million times as massive as the Sun ## Footnote This black hole powers a bright source of radio emission known as Sgr A*.

Astro 18 (12 decks)

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