Unit 2

Provided following are various stages during the life of a high-mass star. Rank the stages based on when they occur, from first to last

- contracting cloud of gas and dust - protostar - main-sequence O star - red supergiant - supernova - neutron star

Provided following are various elements that can be produced during fusion in the core of a high mass main sequence star. Rank these elements based on when they are produced, from first to last.

- helium - carbon - oxygen - iron

Suppose you measure the parallax angle for a particular star to be 0.1 arcsecond. The distance to this star is

10 par sec

what is the average length of time between solar maximums

11 years

What is the overall fusion reaction that converts mass into other forms of energy in the Sun's core?

4 hydrogen nuclei become 1 helium nucleus

According to modern science, approximately how old is the Sun?

4.5 billion

What is the smallest mass a newborn star can have?

80 times the mass of Jupiter

inverse square law

A physical quantity varies inversely as another quantity squared.

radiation zone

A region of very tightly packed gas in the sun's interior where energy is transferred mainly in the form of light.

"white dwarf limit (1.4 solar masses)".

A white dwarf in a close binary system will explode as a supernova if it gains enough mass to exceed the

what causes solar activity

All of these features are created by magnetic fields, which form and change easily in the convecting plasma in the outer layers of the Sun.

What causes the radio pulses of a pulsar?

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

The ____ is the process by which hydrogen fusion proceeds in high-mass stars.

CNO cycle

What element(s) should you expect to be most abundant in the star when it reaches Stage 6?

Carbon At Stage 6 the star has become a white dwarf, which is essentially the leftover core after all fusion has ceased. Because the last stage of fusion was helium fusion, in which helium fuses to make carbon, the white dwarf should be composed largely of carbon. (Some oxygen can also be produced during the late stages of helium fusion, so white dwarfs are often made of both carbon and oxygen.)

Rank the following layers of the Sun based on the pressure within them, from highest to lowest

Core, radiation zone, convection zone, photosphere

Solar Thermostat

Decline in core temperature causes fusion rate to drop, so core contracts and heats up. Rise in core temperature causes fusion rate to rise, so core expands and cools down

Parallax formula

Distance in ly: 3.26ly/parallax angle in arcsec Distance in pc: 1/parallax angle in arcsec Only stars within 120pc have parallax angles great enough to calculate their distance

The star expels its outer layers into space almost immediately upon the end of Stage

During Stage 5 the star has an inert carbon core surrounded by shells of helium and hydrogen fusion. Because the core will never become hot enough for carbon fusion, this is the last stage of the star's life, and at the end of this stage it expels its outer layers as a planetary nebula.

Listed following are the different layers of the Sun. Rank these layers based on their distance from the Sun's center, from greatest to least.

GREATEST: corona, chromoshere, photosphere, convection zone, radiation zone, core LEAST

The most abundant molecule in molecular clouds is

H2

What is interstellar reddening?

Interstellar dust absorbs more blue light than red light, making stars appear redder than their true color

what is brightness and luminosity?

Luminosity is a measure of power, and apparent brightness is a measure of power per unit area.

Which of the following statements about a globular cluster is true?

Most stars in the cluster are yellow or reddish in color.

- usually very strong magnetic field - sometimes appears as a pulsar

Neutron star

The spectral sequence in order of decreasing temperature is

OBAFGKM

Why does the energy produced by fusion in the solar core take so long to reach the solar surface?

Photons take hundreds of thousands of years to get out of the sun because their paths zigzag repeatedly. Because the plasma is so dense, photons can only travel a fraction of a millimeter before colliding with an electron and deflecting in a new direction

Which statement best describes the solar neutrino problem?

Solar neutrinos were detected but in fewer numbers than predicted by theoretical models.

Which statement accurately describes the length of Stage 1 compared to Stages 2 through 5?

Stage 1 lasts nearly 10 times as long as Stages 2 through 5 combined.

During which of the labeled stages on (Figure 1) at left, is the star generating energy through helium fusion in its central core (along with hydrogen fusion in a surrounding shell)?

Stage 4 is the star's helium core-fusion stage, when it generates energy both from helium fusion in the central core and hydrogen fusion in a surrounding shell

Parsec (pc)

The distance to an object with a parallax angle of 1 arcsecond; approximately equal to 3.26 light-years.

Chromosphere

The middle layer of the sun's atmosphere

corona

The outer layer of the sun's atmosphere.

electron degeneracy pressure

The radius of a white dwarf is determined by a balance between the inward force of gravity and the outward push of

What is the energy balance of the sun?

The rate at which energy radiates from the surface of the Sun must be the same as the rate at which it is released by fusion in the core.

Observationally, how can we tell the difference between a white-dwarf supernova and a massive-star supernova?

The spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white-dwarf supernova does not

At which of the first five labeled stages is the star in energy balance?

The star is in energy balance when its core energy production matches the amount of energy it radiates into space. As explained in the video, this is true only when the star is a main-sequence star with hydrogen core fusion and when it is a helium core-fusion star. It is out of energy balance at all other times, which is why it is either contracting or expanding.

Suppose a white dwarf is gaining mass because of accretion in a binary system. What happens if the mass someday reaches the 1.4-solar-mass limit?

The white dwarf undergoes a catastrophic collapse, leading to a type of supernova that is somewhat different from that which occurs in a massive star but is comparable in energy.

Why are Cepheid variables so important for measuring distances in astronomy?

Their luminosity can be inferred from their period

What do we mean when we say that the Sun is in gravitational equilibrium?

There is a balance within the Sun between the outward push of pressure and the inward pull of gravity

Why do sunspots appear dark in pictures of the Sun?

They actually are fairly bright but appear dark against the even brighter background of the surrounding Sun.

What effects are jets and magnetic fields thought to have on a protostar?

What effects are jets and magnetic fields thought to have on a protostar?

What makes us think that the star system Cygnus X-1 contains a black hole?

What makes us think that the star system Cygnus X-1 contains a black hole?

Which of the following correctly describes how the process of gravitational contraction can make a star hot?

When a star contracts in size, gravitational potential energy is converted to thermal energy.

_____________________are no longer generating energy through nuclear fusion

White dwarfs

Which star spends the longest time in the protostellar phase of life?

a 1 solar mass star

Astronomers estimate that new stars form in our galaxy at the rate of about

a few (2-3) per year.

What is the greatest mass a newborn star can have

a few hundred solar masses

Plasma

a gas in which atoms are ionized because of the high temperature. The Sun is essentially a giant ball of hot gas or, more technically...

What is the CNO cycle?

a type of hydrogen fusion that uses carbon, nitrogen, and oxygen atoms as catalysts

Listed following are events or phenomena that occur during either the part of the sunspot cycle known as solar minimum or the part known as solar maximum. Match these items to the correct part of the sunspot cycle

all are solar maximum except : occurs about 5 to 6 years after a solar maximum (on average)

Which of the following statements about apparent and absolute magnitudes is true? A) The magnitude system that we use now is based on a system used by the ancient Greeks over 2,000 years ago that classified stars by how bright they appeared. B) A star with apparent magnitude 1 is brighter than one with apparent magnitude 2. C) The absolute magnitude of a star is another measure of its luminosity. D) A star's absolute magnitude is the apparent magnitude it would have if it were at a distance of 10 parsecs from Earth. E) All of the above are true.

all of the above

Which of the following statements about an open cluster is true?

all stars in a cluster are approx the same age

Sunspots

areas of gas on the sun's surface that are cooler than the gases around them

Why are neutrinos so difficult to detect?

because they rarely interact with matter

what pushes out a star? what is trying to crush a star?

between the outward push of internal gas pressure and the inward pull of gravity.

-viewed from afar, time stops at its even horizon - size defined by its schwarzchild raduis

blackhole

A(n) "white dwarf supernova"

can occur only in a binary system, and all such events are thought to have the same luminosity.

how does parallax depend on distance?

cause of the shift

Which of the following layers of the Sun can be seen with some type of telescope? Consider all forms of light, but do not consider neutrinos or other particles

chromosphere, photosphere, corona

A(n) "accretion disk"

consists of hot, swirling gas captured by a white dwarf (or neutron star or black hole) from a binary companion star.

The following figures show various stages during the life of a star with the same mass as the Sun. Rank the stages based on when they occur, from first to last.

contracting cloud of gas and dust, protostar, main sequence G-star, red giant, planetary nebula, white dwarf

In which of the following layer(s) of the Sun does nuclear fusion occur?

core

what are the layers of the sun?

core, radiative zone, convective zone, photosphere, chromosphere, corona

which of the following is closest in size to a white dwarf

earth

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

either a black hole or a neutron star

There is no upper limit to the mass of a neutron star

false

in order to understand star clusters, we need to be able to estimate their ages. What technique do scientists use for this

finding the main-sequence turnoff point of the stars

Stars that are cooler than the Sun yet 100 to 1,000 times as luminous as the Sun are classified as ______________

giants

Based on its surface temperature of 5,800 K, what color are most of the photons that leave the Sun's surface?

green

Carbon can be converted into oxygen in the cores of high-mass stars if carbon nuclei undergo a _____ .

helium capture reaction

Betelgeuse is a supergiant star that will eventually supernova, which means that by mass it is classified as a ____

high mass star

If you wanted to observe stars behind a molecular cloud, in what wavelength of light would you most likely observe?

infared

absolute magnitude

is the apparent magnitude it would have if it were at a distance of 10 parsecs (32.6 light-years) from Earth

What is the ultimate fate of an isolated white dwarf?

it will cool down and become a black dwarf

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

larger than that of Star B

What type of star is our Sun?

low-mass star

Stars are classified on the basis of their spectral type and ___________________

luminosity class

The ____________________is greater for low-mass stars than it is for high-mass stars.

main-sequence lifetime

Hydrogen fusion in the Sun requires a temperature (in Kelvin) of

millions of degrees

A _____ has a density higher than the density of a white dwarf.

neutron star

What powers the sun?

nuclear fusion

A(n) "massive star supernova"

occurs when fusion creates iron in the core of a star.

A(n) "nova"

occurs when hydrogen fusion ignites on the surface of a white dwarf in a binary system.

Which layer of the Sun do we normally see?

photosphere

Which of the following sequences correctly describes the stages of life for a low-mass star?

protostar, main-sequence, red giant, white dwarf

The arrows on each protostar's curve on the diagram's indicate that __________.

protostars change in surface temperature and luminosity as they develop

Cepheids are examples of ________________________

pulsating variable stars

Corona, Chromosphere, , photosphere, convection zone, radiation zone, core

ranking from outermost layer of sun to inner

If the distance between us and a star is doubled, with everything else remaining the same, the luminosity

remains the same, but the apparent brightness is decreased by a factor of four.

how does the activity of the sun affect earth?

research remains

solar activity

short-lived phenomena on the Sun, including the emergence and disappearance of individual sunspots, prominences, and flares; sometimes called solar weather

when is the sun most active?

solar maximum, when sunspots are most are most numerous

when is the sun least active?

solar minimum- least sunspots

core

source of the Sun's energy: nuclear fusion transforming hydrogen into helium.

The stars known as________________________ are the very largest and brightest of all the stars

supergiants

____ actually occurred about 150,000 years ago in the Large Magellanic Cloud.

supernova 1987a

The debris from the death of a high-mass star forms a ___ several light years across.

supernova remnant

What types of stars end their lives with supernovae

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

What do astronomers mean when they say that we are all "star stuff"?

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

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

the Sun

When we refer to the solar thermostat, we are referring to the idea that __________.

the Sun's core temperature naturally stays stable

what is parallax?

the apparent change in position of an object when you look at it from different places

apparent magnitude

the brightness of a star when viewed from Earth

The energy balance that contributes to the solar thermostat is a balance between

the energy released in the core by fusion and the energy radiated from the Sun's surface into space

Astronomers can measure a star's mass in only certain cases. Which one of the following cases might allow astronomers to measure a star's mass?

the star is a member of a binary star system

Photoshere

the visible surface of the sun

White dwarfs are so called because

they are both very hot and very small

What does Einstein's general theory of relativity tell us about two co-orbiting white dwarfs?

they will emit gravitational waves that carry energy and angular momentum away from the system, causing the white dwarfs to gradually spiral inward toward each other and eventually merge

All pulsars are neutron stars, but not all neutron stars are pulsars.

true

Which of these elements had to be made in a supernova explosion?

uranium

How do we know what happens at the event horizon of a black hole?

we dont know for sure : we only know what to expect based on the predictions of general relativity

When does a protostar become a true star?

when nuclear fusion begins in the core

convection zone

where hot gas moves up toward the surface and cooler gas moves deeper into the interior

- has a mass no greater than 1.4M SUn -typically about the size (diameter) of Earth - in a binary system, it can explode as a supernova -supported by electron degeneracy pressure

white dwarf