Physics 1080 Exam 3

Very young star clusters have main-sequence turnoffs

at the top left of the main sequence

Sunspot structure:

dark umbra with surrounding penumbra.

Left of H-R diagram

hottest stars

Hawking radiation

how black holes lose energy

apparent magnitude

how bright the star appears to us in the sky

When hydrogen is fused into helium, energy is released from

conversion of mass to energy

Sunspots:

cooler (4200 K) areas in the photosphere caused by solar magnetic field loops

absolute magnitude

how bright the star would be at a distance of 10 parsecs from us

The solar wind

creates a teardrop-shaped bubble around the Solar System

Order the following objects from smallest to largest, according to their radii.

1 Msun black hole 1.5 Msun neutron star 1 Msun white dwarf 1 Msun star

Supernova: Core Collapses

1. Core collapses and its temp rises 2. Photodisintegration and neutrino cooling reduce core pressure 3. Collapse accelerates 4. Core collapses until it reaches nuclear densities. 5. Core collapse stops, bounces back, driving a shock wave through star. 6. Shock wave takes only hours to rip through the star

1 arcminute

1/60 of a degree

1 arcsecond

1/60 of an arcminute 1/3600 of a degree

How many years worth of energy in Sun

10 billion

least luminous stars

10^-4 Lsun more common than light luminosity stars

Most luminous stars

10^6 Lsun

Sun shows an __-year sunspot cycle

11

Solar Magnetic field flips every

11 years 22 year cycle

Suppose an atom has three energy levels, specified in arbitrary units as 10, 7, and 5. In these units, which of the following energies might an emitted photon have?

2,3,5

Place the following steps which lead some low-mass stars in binary systems to become novae or supernovae in the correct order. Note that the first step is given. Step 1: Two low-mass main sequence stars orbit each other.

2. Star 1 (the more massive star) begins to evolve on the main sequence 3. Star 1 fills its Roche lobe and begins transferring mass to Star 2 4. Star 2 gains mass, becoming hotter and more luminous 5. A white dwarf orbits a more massive main sequence star 6. Star 2 fills its Roche lobe and begins transferring mass to the white dwarf 7. The white dwarf becomes either a nova or supernova

Highest-mass stars appear to be greater than

200 Mo, but are rare

What nuclei enter the final collision? (If there are multiple nuclei that are the same, only select it once.)

3He

The Sun has been around a long time, about

4.6 billion years

What is the temperature of the test star?

5800 K

_____% of atoms in Sun are hydrogen

90

Newton's Law of Gravity

A less massive star moves faster on a larger orbit

The Sun rotates once every 25 days relative to the stars. The Sun rotates once every 27 days relative to Earth. Why are these two numbers different?

Earth moves in its orbit during this time

In order for an electron to jump up two energy levels in an atom at once, it requires

More energy than to jump up one energy level a precise amount of energy a bluer photon than to jump up one energy level

In a high-mass star, hydrogen fusion occurs via the

CNO cycle

Rank the layers of the Sun in order from lowest to highest density

Convective Zone, Radiative Zone, Core

Are the nearest stars generally hotter or cooler than the Sun?

Cooler

Fusion occurs in the ____ of the Sun

Core

The Sun's structure exhibits many distinct layers. Starting from its center, place the layers in order.

Core Radiative Zone Convective Zone Photosphere Chromosphere Corona

Rank the layers of the Sun in order from highest to lowest temp

Core, Radiative Zone, Convective Zone

________stars emit more energy and run out of hydrogen fuel in their cores faster.

More massive

How does the spectrum of a distant star reveal the star's chemical composition?

Dark lines, also called absorption lines, within the spectra are "fingerprints" for the different atoms and molecules within a star's atmosphere

Electron-degenerate

Describing the state of material compressed to the point at which electron density reaches the limit imposed by the rules of quantum mechanics.

Sort the nuclei below into the nuclei that entered into the reaction and the nuclei that resulted from the reaction.

Entered: Hydrogen and Deuterium Resulted: Helium-3

Think about how you would expect the temperatures in the star to vary between each of the layers shown, and use this to sort the following elements in order of increasing temperature at which they burn in a nuclear fusion reaction.

H He C Ne O S

A pulsar occurs when a neutron star

Has a magnetic axis that is not aligned with the rotation axis

Cepheid variables

High mass stars become supergiants Periods from 1-100 days More luminous stars have shorter periods

Fusion requires:

High temperature, to collide protons together at high speed 2) High densities, to insure collisions.

How does the energy production in a high-mass, main-sequence star differ from energy production in the Sun?

High-mass stars use carbon in a process that fuses hydrogen to helium and High mass stars produce energy at a faster rate

Wien's Law

Hotter means bluer

As you move up the H-R diagram, what happens to the radius

It increases

What is a gamma ray?

It is a high energy photon

If a star is found directly to the right of the Sun on the H-R diagram, what can you conclude about its temp?

It is cooler than the Sun

When the core of a star runs out of fuel and nuclear fusion stops, what will happen to the star?

It will collapse

If it were possible to watch a high-mass star move to the right along one of the post-main-sequence lines, what would happen to the star's size?

It would become much larger

If it were possible to watch a high-mass star move along the topmost of these post-main-sequence lines, what would you observe to be happening to the star in terms of its luminosity?

It would remain about the same

Are the nearest stars generally more or less luminous than the Sun?

Less luminous

RR Lyrae variables

Low-mass stars on the horizontal branch Less luminous than Cepheid variables

Far right of main sequence

M stars: cooler, smaller, and fainter than Sun

Lowest-mass stars have

M= 0.08 Mo

Recall that conservation of angular momentum causes collapsing objects to rotate faster. With that in mind, sort the following objects in order of the rotational speed you would expect them to have when they first form, from slowest to fastest.

Main sequence star white dwarf neutron star black hole

Low-mass stars

Mass is less than 8 Mo

mass transfer.

Material can flow from the giant star to the companion.

Far left of main sequence

O stars: hotter, larger, more luminous than sun

Full sequence

OBAFGKM 10 subgroups (0-9)

What surrounds the white dwarf at the center?

Planetary nebula

Which particle carried away the other positive charge?

Positron

Did the gamma ray ever enter the reaction, or was it produced by the reaction

Produced by the reaction

Why do astronomers think that neutron stars were formed in supernova explosions?

Pulsars sometimes have material around them that looks like the ejecta from supernovae

What changed about the star as you dragged it down the H-R diagram to simulate the White Dwarf phase?

Radius and temperature decrease

What changed about the star as you dragged it across the H-R diagram to simulate Planetary Nebula Ejection?

Radius decreases and temperature increases

Star: larger, more luminous, cooler, redder ->

Red Giant

Which of the following statements most accurately describe your observations of this plot?

Redder main-sequence stars are fainter on average than bluer main-sequence stars. The spectral type of a star uniquely determines its color.

What do the images tell you about the relationship between sunspots and solar flares?

Solar flares happen where there are sunspots

From the vantage point of Earth in the diagram shown, how will the parallax of Star A compare to that of Star B?

Star A has twice the parallax of Star B

An eclipsing binary system has a primary eclipse (star A is eclipsed by star B) that is deeper than the secondary eclipse (star B is eclipsed by star A). What does this tell you about stars A and B?

Star A is brighter than Star B

How do the temperatures of the brightest stars in the sky compare to the temperature of the nearest stars?

The brightest stars are hotter than the nearest stars

Identify the statement that best describes how the latitude of sunspots varies over a sunspot cycle, which is defined to begin at solar minimum.

Sunspots are at higher latitudes at the beginning of a cycle, and lower latitudes at the end of the cycle

As a star leaves the main sequence, it moves up and to the right on the H-R diagram. Grab the cursor (the X on the H-R diagram), and move it up and to the right. How does the test star's temperature change?

Temperature decreases

What triggers a supernova explosion

The "furnace" at the core turns off

Suppose Jupiter were not a planet, but instead were a G5 main-sequence star with a mass of 0.8 MSun. How could this affect the Sun as the G5 star came to the end of its life?

The G5 may have transferred all its mass to the Sun, causing the Sun to explode as a Type I supernova. The Sun would have already become a white dwarf, and as the G5 swelled into a red giant, material from it would be transferred to an accretion disk around the Sun, making the Sun explode as a nova.

Albireo, a star in the constellation of Cygnus, is a binary system whose two components can be seen easily with even a small telescope. Viewers describe the brighter star as "golden" and the fainter one as "sapphire blue." What does this tell you about the relative temperatures of the two stars?

The blue star is hotter than the gold star

How do the luminosities of the brightest stars in the Sky compare to the luminosities of the nearest stars?

The brightest star are more luminous than the nearest stars

The solar corona has a temperature of more than a million kelvins; the photosphere has a temperature of only about 6000 K. Why isn't the corona significantly brighter than the photosphere?

The corona has a much lower density

Which of the following statements about massive stars having the shortest lifetimes is NOT true?

The higher a star's mass, the greater the percent of heavier elements from which it formed, and heavier elements burn hotter and faster.

How will the motion of the red marble placed at the edge of the flat sheet and given an initial velocity in the direction of the arrow compare with its motion on the curved sheet with a large mass in its center?

The marble will travel in a straight line on the flat sheet and in a line curving toward the central mass on the curved sheet

An experienced astronomer can take one look at the H-R diagram of a star cluster and immediately estimate its age. Select the statement that explains how this is possible.

The most massive stars remaining on the main sequence indicate the cluster's age

As you move left across the H-R diagram, what happens to the radius?

The radius decreases

Which of the following describe how a more evolved high-mass star will differ from when it was on the main sequence?

The star will become redder in color, larger in diameter, change spectral type

As a star leaves the main sequence, it moves up and to the right on the H-R diagram. Grab the cursor (the X on the H-R diagram), and move it up and to the right. What changes about the image of the test star next to the Sun?

The test star becomes larger, brighter, and redder

Explosion of White dwarf called

Type 1a supernova

Middle stars

Type A strong hydrogen absorption about 10,000K

Outer layers blow off in tremendous explosion called a

Type II supernova

Cool stars

Type M Many different elements (iron, oxygen, silicon,) or molecules <4500 K

Hottest stars

Type O Weak absorption by hydrogen and helium >20,000 K

Rank the objects from least to greatest mass, according to the stars that produce each.

White Dwarf Neutron Star Black Hole

What is at the center of the nebula?

White dwarf

Pulsar

a rapidly rotating neutron star

Which of the following stars will have the longest lifetime?

a star 1/20 as massive as the Sun

Which of these hypothetical situations would allow the temperature of the Sun's core to rise enough for carbon fusion to be possible?

add mass to the sun

Coronal material flows

along the magnetic field away from the Sun.

In older clusters, high- mass stars have

already died

Absorption

an electron absorbs the energy of a photon to jump to a higher energy level

Emission

an electron emits a photon and drops to a lower energy state, losing energy

Star clusters

are bound groups of stars, all made at the same time. They are "snapshots" of stellar evolution

Outer layers expand and cool ->

asymptotic giant branch of HR diagram

Chromosphere:

ayer directly above the photosphere. ▪ Higher temperature than the photosphere. • Due to magnetic field

Must always maintain ____ between pressure and gravity

balance

The Sun must be in ____________ to exist for billions of years.

balance

Limb darkening

because we look through less material at the edge it appears darker, like an outline.

Most stars are in

binary systems

top of H-R diagram

brightest stars

Electrons can only have

certain energies

Parallax

change in position caused by a change in position of observer

Solar wind:

charged particles flowing away from the Sun through coronal holes, where magnetic field lines extend away from the Sun.

If the mass of a core of a high-mass star is greater than 3 solar masses, it will

collapse to a black hole

Speeds depend on the Sun's

composition and the depth of the convection zone.

Density, pressure, and temperature ______________ away from the center of the Sun.

decrease

High Mass stars:

defined as having mass > 8 solar masses

Degenerate matter is different from ordinary matter because

degenerate-matter object gets smaller as it gets more massive

As the helium core shrinks,

density and temp increase

Special relativity

dictates light moves at a speed c, regardless of their motion

Parsec

distance at which the parallax is equal to one arcsecond 206,000 AU= 3.26 light-years

Each type of atom has a unique set of

energies bookshelf analogy

Photon's energy is equal to the

energy difference between two levels

If a spaceship approaches you at 0.5c, and a light on the spaceship is turned on pointing in your direction, how fast will the light be traveling when it reaches you?

exactly c (speed of light)

Levels above ground state are

excited states

Elements heavier than iron originated in the

explosions of high-mass stars

Fusion of iron or more massive elements requires an

external energy source

More mass -> more pressure -> higher temperatures ->

faster nuclear reaction rates

An accretion disk around a white dwarf in a binary system

feeds material onto the white dwarf

The layers in a high-mass star occur in order of

fusion temperature

Once the star has an iron core, it can

generate more energy by fusion

Stars begin burning helium to carbon when the temperature rises in the core. This temperature increase is caused by

gravitational collapse

Because the helium is not fusing, _____ begins to win over the pressure, causing the helium core to shrink.

gravity

Lowest energy state is called

ground state

The interior of an evolved high-mass star has layers like an onion because

heavier atoms fuse closer to the center, where the temperature and pressure are higher

Eventually much of the hydrogen in the core is converted to

helium

Key difference: heavier elements (C, Ne, O, etc.) can undergo fusion in

high-mass stars

Young clusters still have

high-mass stars on main-sequence.

Solar flares and coronal mass ejections are

highly energetic eruptions

After the helium flash, the stars are on the

horizontal branch of the HR diagram

A white dwarf is located in the lower left of the H-R diagram. From this information alone, you can determine that it is very

hot

prominences

hot rising gas in the chromosphere constrained by magnetic fields

Main-sequence stars fuse ______ and _____ in their cores

hydrogen and helium

If a star has very strong hydrogen absorption lines, that means

hydrogen is abundant in the star because it is absorbing at these wavelengths The temp is right for hydrogen to make lots of transitions

spectroscopic binary

individual stars cannot be resolved in images

As stars expand and cool, they can pass through a portion of the H-R diagram called the

instability strip

Main-sequence turnoff

is the highest mass of stars still on main- sequence.' Location gives cluster age

Star's structure changes when

it uses fuel

Corona

layer above the chromosphere. ▪ Very hot • T=1-2millionK. Emits x-rays can extend for several radii Very low density Only seen with the naked eye during solar eclipses

Convective zone:

layer in between the radiative zone and the surface of the Sun.

Radiative zone:

layer just outside core of the Sun

Photosphere:

layer where the light is emitted into space= apparent surface of the Sun Average temp: 5800 K

A neutron star is

left over from the death of a massive star

Imagine you are on a spaceship. A second spaceship rockets past yours at 0.5 c . You start a stopwatch and stop it 10 seconds later. For an astronaut in the other spaceship, the number of seconds that have ticked by during the 10 seconds on your watch is

less than 10 seconds

Radiation transports energy by moving __________, while convection transports energy by moving __________.

light; matter

Brightness of a star is measured by

logarithmic magnitude

Observed brightness depends on both

luminosity and distance

Sunspots, flares, prominences, and coronal mass ejections are all caused by

magnetic activity on the Sun

What is the single most important property of a star that will determine its evolution?

mass

Star's life depends primarily on

mass and composition

General relativity

mass distorts spacetime

Solar maximum

most sunspots and activity

As Earth orbits the Sun

nearby star change their positions against the background stars

The physical model of the Sun's interior has been confirmed by observations of

neutrinos and seismic vibrations

Type II supernova can leave behind a neutron-degenerate core called a

neutron star mass between 1.4 solar masses and 3 solar masses

The atom an go from one energy state to another but

never have energy in between

As ___________ collects on the white dwarf, nuclear reactions can start on the surface->gets much brighter temporarily ->

nova

A prosper becomes a star when

nuclear fusion begins

Hydrostatic equilibrium:

outward pressure = inward force of gravity at every point in the Sun

Radiative transfer:

photons travel from hotter to cooler regions (light moves energy)

A ___shines because the dust and gas are hot.

planetary nebula

Ejected material creates

planetary nebula

Hertzsprung-Russell diagram

plot of luminosity vs. temperature

The structure of the Sun is caused by a balance between forces due to

pressure and gravity

Hydrostatic equilibrium in the Sun means that

pressure balances the weight of overlying layers

The structure of the Sun is determined by both the balance between the forces due to _______ and gravity and the balance between energy generation and energy _______.

pressure; loss

Fusion process

proton-proton chain

Doppler shifts can be converted into

radial velocities

As energy moves out from the Sun's core toward its surface, it first travels by _______, then by _______, and then by _______.

radiation; convection; radiation

As a star leaves the main sequence, it moves up and to the right on the H-R diagram. Grab the cursor (the X on the H-R diagram), and move it up and to the right. Ordinarily, the hotter an object is, the more luminous it is. In this case, the temperature has gone down, but the luminosity has gone up. How can this be?

radius is smaller

With luminosity and temperature we can calculate

radius of a star

Suppose you are studying a star with luminosity of 7.0000 Lsun and the surface temp of 3300K. According to the H-R diagram, this star is a

red giant

Gravitational waves

ripples that travel through spacetime at the speed of light

Convection:

rising/falling of hot/cool gas

How do supernovae impact their surroundings

shock wave heats interstellar medium most atoms heavier than iron are made in the explosion injecting these elements into the interstellar medium

Black holes

singularities in spacetime gravity so strong that even light cannot escape

Mass of 4 H nuclei is

slightly greater than 1 He nucleus

The greater the parallax the _____ the distance

smaller

Luminosity is usually expressed in the term of

solar luminosity

As the star expands,

some of its material leaves as a stellar wind

Helioseismology:

sound waves move through the Sun, making surface and interior waves.

Emission line

specific wavelength of emitted light

Depth perception comes from

stereoscopic vision

When core shrinks, its gravitational pull gets

stronger

Visual binary

take pictures showing 2 stars \

Higher mass leads to higher

temp and pressure in the core faster nuclear fusions

Absorption lines help determine a star's

temperature, composition, density, pressure

What property of the image of the test star indicates that its temperature has changed?

test star becomes redder

We can find the age of the stars in a cluster from .

the H-R diagram

Luminosity

the amount of light energy emitted by an object star's intrinsic brightness

The temperature and density of the Sun change abruptly at the interface between

the chromosphere and the corona

Energy production peaks in the

the core of the Sun.

Gravitational lensing

the effect of gravity on the path of light

A planetary nebula forms from

the ejection of mass from a low-mass star

The energy required to begin nuclear fusion in a protostar comes from

the gravitational potential energy of the protostar

An astronaut who falls into a black hole would be stretched because

the gravity changes dramatically over a short distance

What is the immovable object in a supernova explosion

the innermost core

Sunspots change in number and location during the solar cycle. This phenomenon is connected to

the magnetic field of the Sun

Once hydrogen is exhausted from the core, the star leaves

the main sequence

Ultimately, the Suns' energy comes from

the mass of hydrogen nuclei

Chandrasekhar limit.

the maximum mass of a white dwarf above which it collapses. Approximately 1.4 solar masses.

For low-mass star binaries

the more massive star evolves first it can only expand so much before it begins to lose material

Only direct way to measure the distance to a star is from

the parallax

The fact that the speed of light is a universal constant forces us completely to rethink classical physics completely. This is an example of

the self-correcting nature of science

Mass loss means that

the star cannot hold onto the outer layers easily

Post-main-sequence stars lose up to 50 percent of their mass because

the star swells until the surface gravity is too weak to hold material

Eclipsing binary

the total light coming from the star system decreases when one star passes in front of the other

Sunspots appear dark because

they are cooler than their surroundings

Spaghettification

tidal forces cause objects falling into the black hole to stretch greatly

Within seconds of helium ignition, the thermal pressure increases

to the point that the helium core literally explodes (helium flash). not seen

Astronomers cannot use parallax to find the distance to most stars. This is because the stars are

too far away

Astronomers use two points in Earth's orbit to get the best possible parallax measurement. Even better measurements would be possible with observations from

two points in orbit of Mars, separated by half a Martian year

As a star leaves the main sequence, its position on the H-R diagram moves

up and to the right

To find the masses of both stars in a binary system, you must find the _____ of each star, the _____ of the orbit, and the average ____ between the stars

velocities; period; distance

Schwarzschild radius

velocity equals the speed of light

In the proton-proton chain, four hydrogen nuclei are converted to a helium nucleus. This does not happen spontaneously on Earth because the process requires

very high temps and pressures

What may happen to a neutron star near this 3 solar mass limit that is in a close binary and is accreting (i.e., stealing) mass from its companion

when the neutron star grows to 3 solar masses, it will collapse

Atmosphere:

where the density drops very rapidly with increasing altitude.

Leftover carbon core of a star is

white dwarf

When the second star is a giant, it can dump material onto the

white dwarf