ISP 205 exam 3

Which two factors primarily determine the characteristics of a star?

its mass and its stage of life

Star A is identical to Star B, except that Star A is twice as far from us as Star B. Therefore...

both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A

Which of the following statements about spectral types of stars is not generally true?

The spectral type of a star can be used to determine its distance.

Sirius is a star with spectral type A and Rigel is a star with spectral type B. What can we conclude?

Rigel has a higher surface temperature than Sirius.

To calculate the masses of stars in a binary system, we must measure their...

orbital period and average orbital distance

HR diagram letters hottest to coolest

OBAFGKM

The approximate main-sequence lifetime of a star of spectral type O is

3 million years

Why do O stars exhibit weak hydrogen absorption lines?

At these high temperatures, nearly all the hydrogen is ionized, and is therefore unable to interact with light.

Approximate composition of stars

3/4 hydrogen, 1/4 helium and 2% heavier elements

The total amount of power (in watts, for example) that a star radiates into space is called its

luminosity

According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples?

its apparent brightness will decrease by a factor of 9

If Star A is closer to us than Star B, then Star A's parallax angle is

larger than that of Star B

what spectral type is our sun

G

what does the HR diagram represent

luminosity and surface temperature

on an HR diagram, stellar radii..

increase diagonally from the lower left to the upper right

On an H-R diagram, stellar masses

can be determined for main sequence stars but not for other types of stars

How is the lifetime of a star related to its mass?

More massive stars live much shorter lives than less massive stars.

What is the common trait of all main-sequence stars

They generate energy through hydrogen fusion in their core

What do we mean by the main-sequence turnoff point of a star cluster, and what does it tell us?

It is the spectral type of the hottest main-sequence star in a star cluster, and it tells us the cluster's age

What is a white dwarf?

the exposed core and remains of a star that ran out of fuel for nuclear fusion. supported by electron degeneracy pressure

The spectral sequence sorts stars according to..

surface temperature

You see two main-sequence stars with the same spectral type. Star 1 is dimmer in apparent brightness than Star 2 by a factor of 100. What can you conclude, assuming there is no absorption of either star's light by interstellar gas or dust?

Star 1 is 10 times more distant than Star 2

Which of the following stars are brightest at ultraviolet wavelengths?

O and B

Which of the following is the most numerous type of main-sequence star?

An M star

On the main sequence, stars obtain their energy by

converting hydrogen to helium

A star of spectral type G lives approximately how long on the main sequence?

10 billion years

Which comparison between low-mass stars and high-mass main-sequence stars is true?

Low-mass stars are cooler and less luminous than high-mass stars.

what is a main sequence turn off point

the point on the HR diagram where the star leaves the main sequence

You observe a star cluster with a main-sequence turn-off point at spectral type G2 (the same spectral type as the Sun). What is the age of this star cluster?

10 billion years

A brown dwarf is

an object not quite massive enough to be a star

What kind of gas cloud is most likely to give birth to stars?

a cold, dense gas cloud

When does a protostar become a main-sequence star?

when the rate of hydrogen fusion becomes high enough to balance the rate at which the star radiates energy into space

What is the approximate range of masses that newborn main sequence stars can have?

0.1 to 150 solar masses

What would you be most likely to find if you returned to the solar system in 10 billion years?

a white dwarf

list the stages of life for a low-mass star in the correct order

protostar, main-sequence star, red giant, planetary nebula, white dwarf

The main source of energy for a star as it grows in size to become a red giant is....

hydrogen fusion in a shell surrounding the central core

Which of these stars does not have fusion occurring in its core?

a red giant

What would stars be like if hydrogen had the smallest mass per nuclear particle?

What would stars be like if hydrogen had the smallest mass per nuclear particle?

What happens when a main-sequence star exhausts its core hydrogen fuel supply?

The core shrinks while the rest of the star expands.

In order to predict whether a star will eventually fuse oxygen into a heavier element, you mainly want to know what fact about the star?

its mass

Why is iron significant to understanding how a supernova occurs?

Iron cannot release energy either by fission or fusion.

what is a protostar

a star that is still in the process of forming

Which part of the electromagnetic spectrum generally gives us our best views of stars forming in dusty clouds?

infrared

The overall helium fusion reaction is..

three helium nuclei fuse to form one carbon nucleus

What is a planetary nebula

gas ejected from a low-mass star in the final stage of its life

After a supernova explosion, the remains of the stellar core

may be either a neutron star or a black hole

Why is Supernova 1987A particularly important to astronomers?

It is the nearest supernova to have occurred at a time when we were capable of studying it carefully with telescopes.

What did Carl Sagan mean when he said that we are all "star stuff"?

that the carbon, oxygen, and other elements essential to life were created by nucleosynthesis in stellar cores

What eventually halts the gravitational collapse of an interstellar gas cloud that forms an object that is massive enough to become a star?

the central object becoming hot enough to sustain nuclear fusion in its core

What is the fate of an isolated brown dwarf?

it will remain a brown dwarf forever.

What percentage of a star's total lifetime is spent on the main sequence?

90%

Compared to the star it evolved from, a red giant is..

cooler and brighter

How many helium nuclei fuse together when making carbon?

3

What happens to the core of a star after it ejects a planetary nebula?

It becomes a white dwarf.

Why does stellar main-sequence lifetime decrease with increasing stellar mass?

Higher core temperatures cause fusion to proceed much more rapidly.

Which element has the lowest mass per nuclear particle and therefore cannot release energy by either fusion or fission?

iron

What happens when the gravity of a massive star is able to overcome neutron degeneracy pressure

the core contracts and becomes a black hole

What types of stars end their lives with supernovae?

stars that are at least several times the mass of the Sun

Which event marks the beginning of a supernova?

the sudden collapse of an iron core into a compact ball of neutrons

After a supernova event occurring in a high-mass star, what is left behind?

either a neutron star or a black hole

Which type of star spends the shortest time as a main sequence star?

O star

Identify the correct sequence of life events for a high mass star.

main sequence, red supergiant, supernova, neutron star

Which of the following properties describes a low-mass star?

has longer lifetimes than high mass stars

The luminosity of light emerging from the star's gaseous surface is equal to the...

rate of energy generated from nuclear reactions in the star's core

How will an isolated, one solar-mass star die?

as a white dwarf

which mass of stars are more common

lower mass

T or F: stars with high masses live longer than stars with lower masses

false

T or F: Stars spend about 90% of their lifetime on the main sequence

True

Degeneracy pressure stops the crush of gravity in all the following except

a very massive main sequence star

A teaspoonful of white dwarf material on Earth would weigh

a few tons

Which of the following is closest in mass to a white dwarf?

the sun

What is the ultimate fate of an isolated white dwarf?

it will cool down and become a cold black dwarf

Suppose a white dwarf is gaining mass because of accretion from a binary companion. What happens if its mass reaches the 1.4 solar mass limit?

the white dwarf suddenly detonates carbon fusion and creates a supernova explosion

what hypothetical observations would contradict our theories about the formation and evolution of white dwarfs?

discovery of a white dwarf with a mass 1.5 times that of the Sun (1.5 Msun)

What is the upper limit to the mass of a white dwarf?

1.4 solar masses

Which of the following is closest in size (radius) to a white dwarf?

the earth

What kind of star is most likely to become a white-dwarf supernova?

a white dwarf star with a red giant binary companion

After a massive-star supernova, what is left behind?

either a neutron star or a black hole

A paperclip with the density of a neutron star would weigh (on the Earth)

more than Mt. Everest

Which of the following is closest in size (radius) to a neutron star?

a city

From a theoretical standpoint, what is a pulsar?

a rapidly rotating neutron star

What causes the radio pulses of a pulsar?

As the neutron star spins, beams of radio radiation sweep through space. If one of the beams crosses the Earth, we observe a pulse.

Parallax

we see this universe differently in June and January because of orbit

how long will the sun live before it runs out of hydrogen

10 ^ 12 years

A 10 solar mass star has a luminosity 100 times that of the sun. How long will it live?

-10^-9

How does the lifetime of a .1 solar mass star compare with the current age of the universe

...

why do luminosities vary so much?

big stars fusion rates are much faster which makes their life shorter

Which statement best describes the main sequence

the main phase of a stars life

what spectral type is the sun

G

what are LTY stars

stars that are not massive enough to fuse hydrogen in their cores

when does the collapsing stop

when gravity is balanced by gas pressure outward

what happens when a star runs out of hydrogen

the core will retract and heat up

in a main sequence star, what happens if the reaction rate increases slightly

expand and cool off

when the sun becomes a red giant will the sun survive?

no it will crash into the sun

if black holes dont suck, then why does gas fall into the black hole

friction in the gas causes it to heat up and lose energy

suppose we see a star in orbit around an object. what info do we need to determine its mass? ***

orbital period and its distance from the object

suppose you fly to just outside the event horizon while your friend stays a safe distance away. when you return, your watch says one hour has passed. How much time has passed according to your friends watch

years

luminosity

apparent brightness, distance energy per second

which stars are fusing Helium in their cores

A stars (main sequence)

what holds stars together

their own gravity