exam 3

Question 1

what is a light year

Answer 1

the distance that light travels in 1 year

Question 2

low luminosity =

Answer 2

low mass

Question 3

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

Answer 3

F and A types

Question 4

Why are low-mass dwarfs so hard to find?

Answer 4

They put out very little light

Question 5

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

Answer 5

True

Question 6

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

Answer 6

infrared

Question 7

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

Answer 7

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

Question 8

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

Answer 8

True

Question 9

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

Answer 9

True

Question 10

What is the spectral classes for stars?

Answer 10

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

Question 11

What is the HR diagram?

Answer 11

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

Question 12

What is temperature also known as?

Answer 12

spectral class

Question 13

How is the HR diagram plotted?

Answer 13

• temperature increases toward the left
• luminosity increases toward the top

Question 14

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

Answer 14

Along the main sequence

Question 15

What does the main sequence tell us?

Answer 15

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

Question 16

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

Answer 16

Low temperature and high luminosity
- supergiants

Question 17

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

Answer 17

White Dwarfs

Question 18

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

Answer 18

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

Question 19

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)

Answer 19

True

Question 20

What 2 quantities determine the structure of stars?

Answer 20

the total mass and composition of a star

Question 21

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

Answer 21

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

Question 22

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

Answer 22

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

Question 23

White dwarfs are dying stars (True/False)

Answer 23

True

Question 24

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

Answer 24

red dwarf stars

Question 25

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

Answer 25

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

Question 26

What are the main properties of white dwarf stars?

Answer 26

extremely dense, small, very hot, low luminosity

Question 27

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

Answer 27

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

Question 28

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

Answer 28

the left-hand edge

Question 29

What does zero-age mean?

Answer 29

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

Question 30

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

Answer 30

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

Question 31

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

Answer 31

When a star's luminosity and temperature begin to change

Question 32

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

Answer 32

its mass

Question 33

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

Answer 33

Massive stars have more fuel which they burn through much quicker

Question 34

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

Answer 34

True

Question 35

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)

Answer 35

True

Question 36

Red supergiants and red giants have "split personalities" because...

Answer 36

their cores are contracting while their outer layers are expanding

Question 37

Bigger stars die faster (True/False)

Answer 37

True

Question 38

Where are Global Clusters located?

Answer 38

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

Question 39

Why kind of stars are found in Global Clusters?

Answer 39

very old stars

Question 40

Where are Open Clusters located?

Answer 40

in the disk

Question 41

Why are Open Clusters considered "open"?

Answer 41

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

Question 42

What are Stellar Associations?

Answer 42

A group of extremely young stars

Question 43

Where are Stellar Associations located?

Answer 43

regions rich in gas and dust required to form new stars

Question 44

What is escape velocity?

Answer 44

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

Question 45

What is the basic "life story" of a star

Answer 45

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

Question 46

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

Answer 46

Yes

Question 47

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

Answer 47

True

Question 48

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

Answer 48

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

Question 49

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

Answer 49

True

Question 50

What is a degenerate star/ white dwarf?

Answer 50

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

Question 51

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

Answer 51

the end of all fusion reactions

Question 52

What makes a star a true white dwarf?

Answer 52

nuclear fusion in the interior has ceased

Question 53

When does a white dwarf become a black dwarf?

Answer 53

when it no longer shines

Question 54

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

Answer 54

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

Question 55

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

Answer 55

True

Question 56

What is a supernova?

Answer 56

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

Question 57

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

Answer 57

10 billion

Question 58

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

Answer 58

nickel

Question 59

What did William Herschel discover about the Milky Way?

Answer 59

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

Question 60

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

Answer 60

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

Question 61

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

Answer 61

central bar / spiral arms

Question 62

what are barred spirals?

Answer 62

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

Question 63

what shape do central bulges take?

Answer 63

peanut

Question 64

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

Answer 64

in the halo

Question 65

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

Answer 65

True

Question 66

what is differential galactic rotation?

Answer 66

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

Question 67

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

Answer 67

Sagittarius A

Question 68

black holes emit no radiation (True/False)

Answer 68

True