CoK 2

Question 1

Most of the bright stars are NOT among the stars that are very close to us. Why then do they look so bright to us?

Answer 1

these stars are intrinsically so luminous that they can easily can be seen across great distances

Question 2

most of the stars we can see with the unaided eye from earth are

Answer 2

more luminous than the sun

Question 3

the most common kinds of stars in the galaxy have

Answer 3

low luminosity compared to the sun

Question 4

two stars that are gravitationally associated and orbit each other are called

Answer 4

binary stars

Question 5

if the most common type of star in our galaxy are M-type “red drawf” stars why don’t we see very many of them in the sky

Answer 5

red drawfs have intrinsically low luminosity so they’re faint and hard to detect

Question 6

how can we tell that what appears like a single star in out telescopes is actually a binary star system

Answer 6

their spectra will contain the absorption line of two stars

Question 7

when one of the stars is moving towards earth in its orbit, we observe

Answer 7

that the lines in its spectrum show a blueshift

Question 8

the HR diagram plots the luminosity of stars against their

Answer 8

surface temperature

Question 9

if a of the stars we can possibly detect could be independently plotted on an HR diagram, 90% of them would fall into the region called

Answer 9

the main sequence

Question 10

white drawfs are very hot but are also very small compared to the main sequence stars. as a result they are located in the _________ region of the HR diagram

Answer 10

lower left

Question 11

on the HR diagram, where would you find the most massive main sequence star

Answer 11

toward the upper left of the main sequence

Question 12

what would be a reasonable classification for a red giant star

Answer 12

M2III

Question 13

in order for a cold atom of hydrogen to emit a 21-cm wave, it must first be in a slightly higher energy state. what event usually kicks the hydrogen atom up to this higher state

Answer 13

gas atoms within the cloud collide

Question 14

an HII region is

Answer 14

a region around a hot star where hydrogen atoms are ionized

Question 15

the red color we see on a lot of phtotgraphs of nubulae comes from

Answer 15

hydrogen

Question 16

Given the presence of dust throughout the disk of the Milky Way Galaxy, what is the best technique for learning about more distant regions of our galaxy’s disk?

Answer 16

Look for radiation at long wavelengths, for example in the infrared region of the spectrum.

Question 17

Interstellar extinction refers to the phenomenon that foreground dust has on the appearance of background stars. In particular, dust can make stars appear ______ and ______ than they would if the foreground dust wasn’t present.

Answer 17

fainter; more red

Question 18

the dust in the dust clouds in interstellar space consists of

Answer 18

pieces of ice ranging from several meters to a kilometer in diameter

Question 19

a Herbig-Haro (HH) object is

Answer 19

where a jet from a star in the process of being born collides with and lights up a nearby cloud of interstellar matter.

Question 20

Astronomers identify the “birth” of a real star (as opposed to the activities of a protostar) with what activity in the star?

Answer 20

When nuclear fusion reactions begin inside its core.

Question 21

when does a protostar “arrive” on the main sequence and “switch on” to become a star?

Answer 21

when it begins fuding hydrogen into helium in its core

Question 22

why do all stars spend most of their lives on the main sequence

Answer 22

stars fuse hydrogen on the main sequence and every star is mostly made of hydrogen

Question 23

As a star’s core contracts, it gets hotter. What happens to the star’s outer layers?

Answer 23

they expand and cool

Question 24

When does a star “leave” the main sequence and begin its post-main sequence evolution?

Answer 24

when the core fuses the last of its hydrogen into helium

Question 25

As a star becomes a giant, its outer layers are expanding. Where does the energy for expanding these layers come from?

Answer 25

from the fusion of hydrogen into helium in a shell surrounding the core

Question 26

when the outer layers of a star like the sun expand, and it becomes a giant, which way does it move on the HR diagram

Answer 26

toward the upper right

Question 27

what happens whne the core of a star reahes a temp of 100 million K

Answer 27

three helium nuclei begin fusing carbon

Question 28

mass of the sun during its lifetime

Answer 28

the sun will lose a significant amount of mass during and after its red giant phase

Question 29

Why is it easier for red giants to lose mass than main sequence stars?

Answer 29

red giants are so big, the gravity at their surface is less

Question 30

why is the lifetime of planetary nebulae so short

Answer 30

because planetary nubulae expand too far from their white drawf and no longer be ionized

Question 31

Planetary nebulae are rich in “metals” such as carbon, nitrogen, oxygen, and even neon. What eventually becomes of this gas?

Answer 31

It dissipates into the interstellar medium and seeds the next generation of stars with “metals”.

Question 32

Compared to a main sequence star, a white dwarf will always

Answer 32

be smaller in radius

Question 33

When a low-mass star (M < 8M⊙) finally dies, it leaves behind

Answer 33

white drawf

Question 34

Which star will leave behind the white dwarf with the smallest radius?

Answer 34

A 2M⊙ star.

Question 35

Even though high mass (> 8 M⊙) stars have far more hydrogen than low mass stars, they run out of their fuel faster and leave the main sequence much sooner. Why is this?

Answer 35

They fuse their hydrogen fuel hotter and faster than low-mass stars

Question 36

Iron fusion cannot support a star because iron

Answer 36

absorbs energy when it undergoes fusion.

Question 37

What prevents the core of a massive star (~ 8 - 20 M⊙) from ultimately collapsing into a black hole?

Answer 37

neutron degeneracy pressure

Question 38

A Type II supernova is also known as

Answer 38

a core-collapse supernova

Question 39

What percentage of the energy in a Type II supernova is released in the form of electromagnetic radiation?

Answer 39

1%

Question 40

Heavy elements are returned to the interstellar medium by ______

Answer 40

• strong stellar winds during the second red giant, or asymptotic giant branch, phase.
• planetary nebulae.
• supernovae

Question 41

A neutron star will be detected from Earth as a pulsar by its regular radio pulses only if Earth lies

Answer 41

almost directly in line with the magnetic axis of the neutron star at some time during its rotation.

Question 42

The synchrotron emission in pulsars comes from _____.

Answer 42

charged particles forced to accelerate by moving along curved paths within a magnetic field

Question 43

The long duration gamma ray bursts likely come from ___ while the short duration GRBs are likely _____

Answer 43

core collapse supernovae with a black hole remnant; merging neutron stars

Question 44

Supernova remnants are the result of shocked gases exploded from a massive progenitor star. Although these gases emit light at all wavelengths, which of these are the most energetic?

Answer 44

x-rays