Chapter 12-15
A visual binary star system has rotation period, P=10 years. The semi-major axis of the orbit of one of the stars is 5 AU. What is the combined mass of the binary star system?
8 solar masses
The Sun will leave the main sequence in about ___ years from now.
5 billion
A star has a parallax angle of 0.2 arc seconds, which means it is at a distance of
5 parsecs
A star radiates most strongly at 400 nanometers. What is its surface temperature?
7,250 K
The Sun is composed of about ____ and ___ plus 2% other elements
71% hydrogen 27% helium
The strong gravitational field of a white dwarf slows down the speed of escaping light, and results in the gravitational redshift.
False
Wien's law implies that a blue star is cooler than a red star.
False
The ___ a period ____, that coincides with ____.
Maunder Minimum is; of low sunspot activity; the "little ice age" in the late 17th century
The magnetic fields in sunspots can be detected by the fact that some lines in the spectrum of a gas split into two or more lines by the action of magnetic fields.
True
The fast rotation of neutron stars is a consequence of the law of conservation of angular momentum.
True
The hottest (O and B type) stars are usually binary stars, while the coolest (M type) stars are usually single stars.
True
The ideal gas law implies that raising the temperature and density of a gas increases the pressure of the gas.
True
The interior of a white dwarf behaves like a degenerate gas, i.e., the temperature has little effect on the pressure.
True
The luminosity class of. astra can be determined from the width of the spectral lines of the star.
True
The masses of stars are generally in the range of 30 to 0.1 solar masses.
True
The pulsation in the luminosity of variable stars is driven by the changing opacity of their atmosphere.
True
The spectral lines of white dwarfs are redshifted, because their high gravity reduces the energy carried by light escaping from the white dwarf.
True
The study of an eclipsing binary star systems provides information about the radii of stars
True
The surface temperature of a white dwarf is higher than the surface temperature of the Sun.
True
From the center out, the correct order of the parts of the Sun is
core, radiative zone, convection zone, photosphere, chromosphere, corona.
The solar wind is created in the Sun's ___
corona
What is the Sun's outermost atmosphere called?
corona
The luminosity of a star is determined by the star's ____ and _____
diameter; surface temperature
The method of standard candles can be used to measure a star's ___.
distance
The diameter of the Sun is determined by measuring its ____ and ____.
distance; angular size
____ binary star systems are important because they allows astronomers to determine the mass and the ___ of the stars in the system
eclipsing; diameter
Black holes emit radiation in the form of ______ waves known as Hawking radiation.
electromagnetic
Generally speaking, activity on the surface of the Sun is primarily driven by
electromagnetism.
When a massive star begins to run out of hydrogen to fuse, its outer layers of gas ____.
expand and cool
Two important properties of young pulsars are
extremely rapid rotation and a strong magnetic field.
The Sun rotates _____ at its equator than at its poles.
faster
The Sun produces its energy through ___
fusion of hydrogen into helium
The main source of energy in main sequence stars is
fusion of hydrogen to helium
The Sun's core is generating energy in the form of ____.
gamma rays
If a spinning object's radius shrinks by a factor of 5, its rotation velocity will
get five times faster
The escape velocity inside a black hole is
greater than the speed of light
Why do white dwarfs have high temperatures?
heat left over from their formation
The triple alpha process produces energy by fusing ___ into ____
helium; carbon
White dwarfs have a surface composed of a thin layer of ____________.
hydrogen and helium
The CNO cycle produces energy by fusing
hydrogen into helium
The Sun's composition by the % of mass is 71% ____, 27% ___, and 2% ___.
hydrogen; helium; other elements
Compared to the Sun, white dwarfs have higher ____ and lower ____.
surface temperatures; luminosities
Luminosity (absolute brightness) of a star depends on its ___________.
temperature and radius
During a star's main sequence portion of its life it does not change size appreciably. This observation indicates that
the Sun produces about the same amount of energy as it radiates into space
Although the Sun's core has a density much greater than rock it is considered a gaseous object because...
the Sun's high internal temperature prevent the atoms from bonding together to form a liquid or a solid
Stars on the main sequence have different luminosities because
they have different masses
A M type star 1,000 times more luminous than the Sun will be located near the ___ part of the H-R diagram.
top right
The star Aldebaran is cooler and much more luminous than the Sun. Where do you expect to find Aldebaran in the H-R diagram?
top right
The temperature at the ___ of the Sun's chromosphere is higher than the temperature ____.
top; at the base of the chromosphere
The Sun converts mass to energy through the proton-photon chain.
True
The Sun is a G2V type star.
True
The Sun rotates slower near its poles than near its equator
True
Why do sunspots appear dark?
they are cooler than their surroundings
A star has a parallax of 0.04 arc seconds. What is its distance?
25 parsecs
A star of absolute magnitude ___ appears 2.51 times brighter than a star of apparent magnitude 4
3
Approximately how massive is the Sun as compared to the Earth?
300,00 times
The mass of an entire hydrogen atom is converted into energy during the proton-proton chain.
False
The more mass a white dwarf has the larger it is.
False
The more massive a star is, the longer it lives because it has more hydrogen to fuse into helium
False
The sequence OBAFGKM orders the stars in decreasing temperature and decreasing mass.
False
What is a planetary nebula?
It is a shell of gas ejected from a star late in its life.
Millisecond pulsars rotate about ______ times per second.
1,000
How big is the Sun compared to the Earth, by diameter, approximately?
100 times bigger
About how long is the solar cycle (evidenced by sunspots)
11 years
The temperature of the Sun's core is about ____
15,000,000 K
The Sun is about how far from Earth?
150,000,000 km
Approximately how long does energy take to the travel from the core to the surface of the Sun?
16 million years
Light travels for about ___ to reach the Sun's surface from the Sun's core, and about ___ to reach the Earth from the Sun's surface
16 million years; 8 minutes
A star of apparent magnitude 6 appears ___ times brighter than a star of apparent magnitude 7
2.51
The Sun rotates now with a rotation speed of about 2 km/sec. If its radius shrank to the size of the Earth, about how fast would it spin?
200 km/sec
About how long is the solar cycle (evidenced by the polarity of the Sun's magnetic field)?
22 years
Why can high-mass stars "burn" helium more easily than low-mass stars?
A high-mass star's core is already very hot, so it already needs to compress its core a little to burn helium.
What is a pulsating star?
A star whose luminosity changes as it regularly expands and contracts
A star that is hot and has low luminosity must have ___________________.
A very small radius
When a high-mass star's core collapses the star could
All of these choices are correct
Which of the following is a remnant of a dying star?
All of these choices are correct
Which of the following statements about the helium flash is correct?
All of these choices are correct
What determines how rapidly a star burns up its fuel?
All of these choices are correct.
What makes a gas cloud contract to form stars?
All parts of the cloud are gravitationally attracted to all other parts, collapsing the cloud
What is the main sequence?
An approximately straight line on the H-R diagram along which most stars lie.
The solar cycle is a result of the
Differential rotation of the Sun
Parallax measurements of the distances to the nearest stars use _____ as a baseline.
Earth's orbit
The mass of a black hole can be determined by _____________.
Applying the modified version of Kelper's Third Law, if the black hole is in a binary system
Which of the following stars has the hottest stellar surface temperature?
B2
A Type la supernova results in the formation of a neutron star.
False
A black hole is an object with escape velocity about half the speed of light.
False
A chunk of material from the interior of a white dwarf would weigh about 100 times more than an Earth rock of the same size.
False
A star approaching the Earth will show spectral lines that are shifted to longer wavelengths
False
According to the ideal gas law, the only way to have high pressure is by having high density.
False
All stars ultimately leave behind a white dwarf and an expanding planetary nebula after they exhaust their nuclear fuel.
False
Comparison of the number of sunspots and the surface temperature of the Earth shows a correspondence right up to the present day.
False
Convection in the outer layers of a star like the Sun helps mixing and makes more hydrogen available for burning.
False
If the Sun were instantly replaced by a black hole of the same mass as our Sun, the Earth would be sucked into the black hole.
False
Interstellar clouds usually form groups of stars that leave the main sequence at the same time
False
Massive stars burn their fuel less rapidly than low-mass stars.
False
Measuring stellar masses using binary stars is difficult because binary stars are rare.
False
Neutron stars must have a mass smaller than the Chandrasekhar limit.
False
Pulsars are rotating white dwarfs
False
The apparent magnitude of a star tells us how bright the star would appear if placed at a distance of 10 pc from the Sun.
False
The average density of the Sun is about the same as that of Jupiter.
False
The light produced in the Sun's core is able to pass freely through the Sun.
False
___ is the most significant force that determines the evolution of stars
Gravity
Which of the following statements about the evolution of high-mass stars is NO T correct?
High-mass stars stop fusing elements once they reach a carbon-filled core
What is the difference between spectroscopic and visual binaries?
In a visual binary we can see two distinct stars; in spectroscopic binaries, the images of the two stars can not be resolved.
____ can be used to measure the ____ of nearby stars.
Interferometry; radius
What makes a star stop contracting?
It gets hot enough that its pressure builds up, pushing back against the force of gravity.
Which of the following stellar spectral types is cooler than our Sun?
K
What stars form the slowest?
K and M
Which of the following stars is reddish in color?
K9
Which of the following statements would explain the fact that larger molecules, such as amino acids, do not produce spectral lines in the OBAFGKM classification?
Larger molecules break apart at the high temperatures of stellar atmospheres.
Lines from molecules are strongest in ___ type stars.
M
The Chandrasekhar limit is the largest ____ a white dwarf can have.
Mass
Since nuclear fusion in the Sun creates energy from matter, why doesn't it violate the law of conservation of energy?
Matter and energy are equivalent, as expressed by Einstein's equation E=mc^2
Why are astronomers interested in detecting neutrinos from the Sun?
Neutrinos give information about the nuclear reactions in the Sun's core.
Which of the following can actually escape a black hole?
None of these choices are correct
What makes a star shine?
Nuclear fusion of light elements
Which of the following stars in hottest?
O
Eighty percent of ____ type stars have orbiting companions.
O and B
The energy released when a star explodes in a supernova can be more than the nuclear fusion energy produced by the same star throughout its entire lifetime.
True
Sunspots are dark because they are
Slightly cooler regions meaning they emit less light than the surrounding areas
Star A and Star B have the same temperatures, but Star A is more luminous than Star B. Based on this information, which of the following must be the case?
Star A is larger than Star B.
At which observatory listed below are scientists trying to capture neutrinos?
Super Kamiokande, Japan
Which is denser?
The Earth (a solid object)
Which is more massive?
The Sun (a gaseous giant)
Why does the number of sunspots change over time?
The Sun's magnetic field changes in strength and shape with time.
Why does the star's core get hotter as the core shrinks?
The core is compressed and compression heats a gas
The spectrum of a star shows the 656 nm absorption line shifted to 658 nm. Which of the following can we conclude about this star?
The star is approaching us with an approximate speed of 900 km/sec
What holds the Sun together?
The sun's gravity
How is the composition of the Sun today different than when it was formed 4.6 billion years ago?
There is now more helium and less hydrogen.
What characteristic do all stars on the main sequence share?
They are all fusing hydrogen into helium in their cores.
What happens to the star's outer layers as the fuel in its core is used up?
They expand and cool
Why are supernova explosions important for our existence?
They liberate from the star's core the heavy elements of which we and Earth are made.
A gravitational wave can carry energy away from two very dense objects if they are orbiting each other or collide.
True
A star of absolute magnitude 1 is about 2.51 times more luminous than a star of absolute magnitude 2.
True
As stars evolve their temperature and luminosity changes, therefore their spectral type (OBAF, etc) changes as well.
True
Astronomers use theory to determine the temperature of the Sun's core, because they cannot measure the core temperature directly.
True
Before turning into a white dwarf, a star like the Sun will spend most of its life as a main sequence star
True
Coronal holes are cooler parts of the corona from which the solar wind escapes.
True
In the core of high-mass stars the energy is transported by convection currents.
True
Iron does not release energy when it is fused.
True
Large interstellar clouds can collapse to form several stars approximately at the same time.
True
Main sequence stars are in hydrostatic equilibrium
True
Nova explosions involve a binary system of a white dwarf and a companion star and can occur in the same system repeatedly.
True
One method of measuring the distance between the Earth and the Sun is by bouncing radar waves off the Sun.
True
One parsec is equal to 3.26 light years
True
Red giants are huge because their outer layers have expanded to a very low density tenuous atmosphere
True
Seismic waves observed at the surface of the Sun provide clues about the temperature and the density of the solar interior.
True
Starting from the core, the internal temperatures of the Sun decreases gradually until reaching the photosphere.
True
Stellar luminosities vary much more than stellar masses
True
The temperature of a protostar can reach 1,5000 K but they are very hard to detect in visible wavelengths because of their low luminosity and because they are surrounded by dust.
True
Typically, if the mass of a white dwarf increases, the white dwarf shrinks and then explodes if the mass exceeds 1.4 solar masses.
True
White dwarfs have magnetic fields as much as 100 million times larger than the Earth's magnetic field.
True
A ____ happens when a single high-mass star explodes.
Type II supernova
In ____ stars most of the electrons in the hydrogen atom are above level 2 and in ___ stars most of the electrons are below level 2, therefore the ___ are essentially absent in both types.
Type O, Type M; Balmer Lines
A ____ happens when a white dwarf in a binary system accumulates more mass than the Chandrasekhar limit.
Type la supernova
The law of conservation of angular momentum states that when an object of a fixed mass changes its radius R, its rotation velocity V, will change so that
VR = constant
If stars rotate with periods of tens of days, why does a neutron star rotate several to thousands of times a second?
When a neutron star collapses, its rotation rate speeds up because of conservation of angular momentum
When do we say that a star is born?
When fusion of hydrogen atoms into helium atoms start
Type la supernovas involve a ____
White dwarf
____ are hot compact stars whose mass is comparable to the Sun's and size to the Earth.
White dwarfs
This recurring event happens in the case of a binary system in which one of the companions is a neuron star.
X-ray bursts
A solar prominence is essentially
a plasma confined to a magnetic tube sticking out of the surface of the Sun
What kind of object does a main sequence star become on first using up its core hydrogen?
a red giant
A cool but very luminous star must have
a very large radius
What is a T-Tauri star?
a young star that exhibits variable light and outflowing gas
The parallax of a star is ___ usually measured in ____.
an angle; arc seconds
A light source at a distance of 1 meter that emits 50 Watts of visible radiation has the same ____ as a source emitting 200 Watts and is located ____.
apparent brightness; 2 meters away
The relative brightness of the stars as we see them in our sky is represented by their
apparent magnitude
Gravitational waves
are traveling distortions of space and time
A ____ is a region where jets of gas from young stars impact and heat the gas surrounding the young star.
bipolar outflow
Differences in apparent magnitude correspond to ratios of
brightness
How do astronomers test models of stellar evolution?
by comparing the paths in the H-R diagram predicted by models with the H-R diagrams of star clusters
The change in rotation rate of a spinning object caused by its size change is a consequence of
conservation of angular momentum
As a star like the Sun evolves into a red giant, its core
contracts and heats
When a massive star begins to run out of hydrogen to fuse, its core ___
contracts and heats
The Sun's energy comes from ___.
conversion of mass into energy
If left in isolation a white dwarf will eventually
cool off and become a black dwarf
What is the escape velocity at the event horizon of a black hole?
speed of light
A protostar is not ____.
hydrostatic equilibrium
When a spinning object changes its size, its rotation rate
increases or decreases, depending on whether it shrinks or expands
Because protostars are at a low temperature and surrounded by dust and gas, astronomers must observe them with ____________.
infrared and radio telescopes
Protostars shine brightest in
infrared spectrum
The Sun formed from the gravitational collapse of a cold ___.
interstellar cloud
From what do stars form?
interstellar clouds
The photosphere
is the layer of the Sun where it transitions from being opaque to transparent
After a star leaves the main sequence, ______________________.
it now fuses hydrogen into helium in a shell outside the core
What of the following most directly determines how much fuel a star has?
its mass
What determines how long a star stays on their main sequence?
its mass and luminosity
If a star is in hydrostatic equilibrium
its radiation pressure outwards and gravitational forces inwards are in balance.
The temperature of black holes is estimated to be ____.
less than 1 millionth of a degree
A method for identifying a black hole is to
look for their effects on nearby companions.
The amount of energy emitted by a star each second is the ___ and is measured in ____.
luminosity; watts
The Zeeman effect, in which energy levels of electrons are shifted and produce a corresponding split in spectral lines are observed, is used to measure ___ at the Sun's surface.
magnetic field strength
In comparison to main sequence stars, which of the neutron star properties listed is not considered extreme.
mass
The most important property that determines the evolution of a star is its
mass
A binary star is a pair of stars that orbit around each other. By detecting this orbital motion, and using Kepler's Laws and the Law of Gravitation, one can directly measure the stars'
masses
Binary star systems are very important because they allow
measurement of star masses
One way to probe the rate of nuclear reactions in the center of the Sun is by studying the ___ produced because _____.
neutrinos; they pass out of the Sun without undergoing a random walk
___ are hot compact remnant stars whose mass is typically between one and several times that of the Sun, but their size is only 10 km or less.
neutron stars
This event recurs and happens when one of the companions in the binary system is a white dwarf.
nova
What powers the Sun?
nuclear fusion of hydrogen into helium
The process in which two or more lighter elements combine to form a single heavier element is called
nucleosynthesis
Brown dwarfs are
objects massive enough to fuse deuterium but not massive enough to sustain hydrogen fusion
If Star A is twice as far as Star B, and they are identical in all other ways, then the brightness of Star A would be
one-fourth the brightness of Star B
In the Sun, nuclear fusion occurs
only in the core
What is the visible surface of the Sun called?
photosphere
Which part of the Sun is covered with granules?
photosphere
The first pulsars were observed using _______ telescopes.
radio
After the hydrogen in the star's core is depleted the core
shrinks and heats up
If a star has an apparent magnitude of 8 and an absolute magnitude of 6 it is
slightly farther than 10 parsecs away
An isolated black hole will
slowly evaporate away through the emission of Hawking radiation.
Astronomers use ____ to determine the magnetic field of white dwarfs.
the Zeeman splitting of spectral lines
The study of eclipsing binary stars is very important because it allows astronomers to determine
the diameters of stars
Hydrostatic equilibrium is a balance between ____ of a star and ___.
the internal pressure; gravity
The fast rotation of neutron stars is a consequence of
the law of conservation of angular momentum
What distinguishes the spectral type of a star?
the lines in its spectrum
In which stage of a star's evolutionary cycle
the main sequence
A main sequence star has 3 times the mass of the Sun. Using ____ we find that the star is ____ times more luminous than the Sun.
the mass-luminosity relation; 9
The period-luminosity law of pulsating variable stars indicates that
the more slowly a star pulsates, the more luminous it is
What is the specific 3-step energy generating process in the Sun called?
the proton-photon chain
If a star exhibits no Doppler shift in its emitted light, it must be true that _______________.
the star is neither moving toward nor away from the Earth
What is solar seismology?
the study of the Sun's interior by analyzing waves in the Sun's atmosphere
Which of the following gives evidence of the solar wind?
the tails of comets
Nearby stars have larger parallax angles, therefore their distances in parsecs are smaller.
true
If the Sun's rotation carries two sunspots around the side out of sight, you might see them again in about
two weeks
Where are red giants on the H-R diagram?
upper right
Astronomers know what the solar interior is like by
using locally-tested physics combined with observations to build a mathematical model of what the Sun should be like in its interior
The Balmer lines correspond to wavelengths in the ____ part of the spectrum of a ____ atom.
visible; hydrogen
In which binary system can we observe both the stars separately and follow their orbits around each other?
visual binary system
What is left when a planetary nebula dissipates?
white dwarf
When the outer envelope of a red giant escapes, the remaining carbon core is called a
white dwarf
Which of the following objects do you expect to find at the center of planetary nebula?
white dwarf
____ are remnants of low-mass stars.
white dwarfs
Yellow dwarfs have ____ spectral lines than red giants.
wider