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intro to the universe > exam 3 > Flashcards

exam 3 Flashcards

1
Q

what is a light year

A

the distance that light travels in 1 year

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2
Q

low luminosity =

A

low mass

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3
Q

What 2 types of stars in our local neighborhood are more luminous and massive than the Sun?

A

F and A types

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4
Q

Why are low-mass dwarfs so hard to find?

A

They put out very little light

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5
Q

Stars fainter than the Sun cannot be seen with the unaided eye, unless they are very nearby (True/False)

A

True

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6
Q

Why type of telescopes help find cool, low-mass stars?

A

infrared

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7
Q

Why are the stars that appear the brightest to us not the closest to us?

A

they emit a very large amount of energy that they don’t have to be nearby to look bright

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8
Q

The vast majority of stars are much smaller and fainter than our Sun (True/False)

A

True

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9
Q

The temperature and luminosity of stars are related (True/False)

A

True

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10
Q

What is the spectral classes for stars?

A

A system used to categorize stars based on the characteristics of their light spectrum, primarily determined by their surface temperature
- The temperature defines the star’s “color” and surface brightness

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11
Q

What is the HR diagram?

A

A scatter plot that graphs the relationship between a star’s luminosity (brightness) and its surface temperature

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12
Q

What is temperature also known as?

A

spectral class

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13
Q

How is the HR diagram plotted?

A
  • temperature increases toward the left
  • luminosity increases toward the top
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14
Q

The majority of stars in the H-R diagram are seen where?

A

Along the main sequence

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15
Q

What does the main sequence tell us?

A

Hotter stars are more luminous than cooler stars
- relationship between temperature and luminosity

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16
Q

Stars in the upper-right region of the H-R Diagram have what?

A

Low temperature and high luminosity
- supergiants

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17
Q

What type of stars are in the lower-left part of the H-R diagram with high surface temperatures and low luminosity?

A

White Dwarfs

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18
Q

Why is it difficult to plot a representative H-R diagram?

A

most stars are so faint that we cannot see those outside of our immediate neighborhood

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19
Q

90% of all stars are located on the main sequence, meaning that stars must spend 90% of their lives in that activity or life stage (True/False)

A

True

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20
Q

What 2 quantities determine the structure of stars?

A

the total mass and composition of a star

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21
Q

Stars located at the upper left part of the H-R Diagram are what?

A

stars with the largest masses that are the hottest and most luminous

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22
Q

Stars located at the lower right part of the H-R Diagram are what?

A

least massive stars that are the coolest and have the least luminosity

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23
Q

White dwarfs are dying stars (True/False)

A

True

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24
Q

What type of stars is more abundant in the solar neighborhood?

A

red dwarf stars

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25
Q

What type of stars are most commonly observed to the unaided eye?

A

main sequence stars, like our Sun, which are bright and relatively close to Earth

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26
Q

What are the main properties of white dwarf stars?

A

extremely dense, small, very hot, low luminosity

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27
Q

Once a star has reached the main-sequence stage of its life, it derives its energy from the conversion of….

A

hydrogen to helium from the process of nuclear fusion in its core

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28
Q

Where is the zero-age main sequence located on the H-R Diagram?

A

the left-hand edge

29
Q

What does zero-age mean?

A

It marks the time when a star stops contracting, settles onto the main sequence, and begins to fuse hydrogen in its core

30
Q

What does the zero-age main sequence on the H-R Diagram show?

A

it shows where stars of different masses but similar chemical composition can be found when they begin to fuse hydrogen

31
Q

When does a star move away from the zero-age main sequence?

A

When a star’s luminosity and temperature begin to change

32
Q

What dictates how many years a star remains in the main-sequence band?

A

its mass

33
Q

Why do more massive stars have shorter lifetimes that lower mass stars?

A

Massive stars have more fuel which they burn through much quicker

34
Q

Stars spend around 90% of their lives fusing hydrogen into helium (True/False)

A

True

35
Q

The expansion of a star’s outer layers causes the temperature at the surface to decrease, making the star’s color become redder (True/False)

A

True

36
Q

Red supergiants and red giants have “split personalities” because…

A

their cores are contracting while their outer layers are expanding

37
Q

Bigger stars die faster (True/False)

A

True

38
Q

Where are Global Clusters located?

A

In the Halo and central buldge
- very far from the Sun

39
Q

Why kind of stars are found in Global Clusters?

A

very old stars

40
Q

Where are Open Clusters located?

A

in the disk

41
Q

Why are Open Clusters considered “open”?

A

the stars usually appear well separated from one another, even in the central regions

42
Q

What are Stellar Associations?

A

A group of extremely young stars

43
Q

Where are Stellar Associations located?

A

regions rich in gas and dust required to form new stars

44
Q

What is escape velocity?

A

the speed needed to overcome the gravity of some object or group of objects

45
Q

What is the basic “life story” of a star

A

starts as a protostar, then lives most of its life as a main sequence star, and eventually moves off the main sequence towards the red-giant region

46
Q

Are low-mass stars more common than high-mass stars?

A

Yes

47
Q

Global Clusters have a relatively small abundance of elements heavier than hydrogen and helium (True/False)

A

True

48
Q

What is the final event in the life of the core?

A

the collapse/contracting of the core due to an absence of helium leaving the star without a source of pressure to balance the gravity

49
Q

White dwarfs are far denser than any substance on Earth (True/False)

A

True

50
Q

What is a degenerate star/ white dwarf?

A

A highly compressed state of electrons where all available energy levels are filled, preventing further collapse due to gravity

51
Q

when is it considered to be the time of a star’s death

A

the end of all fusion reactions

52
Q

What makes a star a true white dwarf?

A

nuclear fusion in the interior has ceased

53
Q

When does a white dwarf become a black dwarf?

A

when it no longer shines

54
Q

Whether or not a star becomes a white dwarf depends on what?

A

how much mass is lost in the red-giant earlier phases of evolution

55
Q

White Dwarfs have masses less than 1.4 (True/False)

A

True

56
Q

What is a supernova?

A

a massive explosion that occurs when a star reaches the end of its life

57
Q

At their maximum brightness, the most luminous supernovae have about _____ times the luminosity of the Sun

A

10 billion

58
Q

One of the elements formed in a supernova explosion is radioactive ________

A

nickel

59
Q

What did William Herschel discover about the Milky Way?

A

it has the shape of a disk / wheel, and the Sun must be near the hub of the wheel

60
Q

Why did Herschel incorrectly conclude that the Sun must’ve been near the hub of the wheel?

A

because interstellar dust absorbs the light from stars, Herschel could see only those stars within about 6000 light-years of the Sun

61
Q

The stars, gas, and dust are not spread evenly throughout the disk but are concentrated into a ________ and a series of ________.

A

central bar / spiral arms

62
Q

what are barred spirals?

A

galaxies with that have bar-shaped concentrations of stars in their central regions

63
Q

what shape do central bulges take?

A

peanut

64
Q

Where are the thin and thick disks, and central bulge located?

A

in the halo

65
Q

Our galaxy has 2 major spiral arms (True/False)

A

True

66
Q

what is differential galactic rotation?

A

stars and matter in larger orbits in the galaxy trail behind those in smaller ones

67
Q

the very bright radio source in the nucleus of the galaxy is known as what? (black hole)

A

Sagittarius A

68
Q

black holes emit no radiation (True/False)

A

True

69
Q
A

intro to the universe (3 decks)

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