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