final exam HW solutions
After it experiences a "helium flash" a star like the Sun will have a brief period of stability, fusing helium into carbon (and sometimes oxygen). During this brief stable stage, the star
none of the above - gets to be even larger in diameter than it was as a red giant -increases tremendously in luminosity -is able to fuse many of the heaviest elements (such as iron and gold) in its superhot core -returns to the position on the H-R diagram that the star had in its main-sequence stage
Where in the Sun does fusion of hydrogen occur?
only in the core
What do we call the antiparticle of the electron (e+)?
positron
A white dwarf, compared to a main sequence star with the same mass, would always be
smaller in diameter
An H-R Diagram plots the luminosity of stars against their
surface tempetature
When a star first begins the long path toward becoming a red giant, a layer of hydrogen around the core begins to undergo fusion. If this layer was too cold to do fusion throughout the main sequence stage, why is it suddenly warm enough?
the core is collapsing under its own weight and heating up from the compression; this heats the next layer up
Which of the following is a characteristic of degenerate matter in a white dwarf star?
the electrons get as close to each other as possible and resist further compression
The region around a black hole where everything is trapped, and nothing can get out to interact with the rest of the universe, is called
the event horizon
Ninety percent of all stars (if plotted on an H-R diagram) would fall into a region astronomers call
the main sequence
In the formula E = mc^2, the letter c stands for
the speed of light
Which of the following statements is FALSE about gamma-ray bursts?
they can currently be used to measure cosmological distances in our universe
When the core of a star reaches a temperature of about 100 million degrees (K), something new happens in the core. What is this new event?
three helium nuclei begin fusing carbon (element number 6)
Which of the following supernovae types can be used for measuring distances throughout our universe?
type Ia
According to Kelvin and Helmholtz, if gravitational contraction alone could explain the Sun's total energy output over the course of its entire life, what is the life expectancy of our Sun?
100 million years
What is the formula for the first step (Step 1) in the proton-proton chain?
1H + 1H → 2H + e^+ + ν
What is the formula for the second step (Step 2) in the proton-proton chain?
2H + 1H → 3He + γ
What is the formula for the third step (Step 3) in the proton-proton chain?
3He + 3He → 4He + 1H + 1H
What scientist devised the equation that tells us how mass and energy can be converted between each other?
Albert Einstein
Who devised these spectral classes (as well as the mnemonic)?
Annie Jump Cannon
A white dwarf with a surface temperature of around 30,000 Kelvin will be a very luminous star
Flase
What is the spectral class (including its sub-class) of our Sun?
G2
Someone suggests that astronomers build a special gamma-ray detector to detect gamma rays produced during the proton- proton chain in the core of the Sun, just like they built a neutrino detector. Explain why this would be a fruitless effort
Gamma rays produced in the center of the Sun are absorbed and re-emitted so many times that they almost never escape the Sun
The event horizon of a black hole is also referred to as the black hole's
Schwarzschid Radius
As our Sun goes through its dying phases, its core will still never become hot enough to fuse Carbon
True
At the end of the p-p chain of nuclear fusion in the Sun, hydrogen nuclei have been converted into
a helium nucleus
According to the formula E = mc^2
a little bit of mass can be converted into a substantial amount of energy
Deep inside a black hole (and hidden from our view) is the compressed center, where all the "stuff" of the star goes. Astronomer call this central point
a singularity
A group of graduate students, bored during a cloudy night at the observatory, begin to make bets about the time different stars will take to evolve. If they have a cluster of stars which were all born at roughly the same time, and want to know which star will become a red giant first, which of the following stars should they bet on?
a type O main sequence star
The event in the life of a star that begins its expansion into a giant is
almost all the hydrogen in its core that was hot enough for fusion has been turned into helium
Why can a star with a mass like our Sun not fuse (produce) further elements beyond carbon and oxygen?
because they just cannot get hot enough for the fusion of heavier nuclei
Two stars that are physically associated (move together through space) are called
binary stars
Two stars that are physically associated (move together through space) because they are gravitationally bound to one another are called
binary stars
As the core of a low-mass star is becoming a white dwarf, the rest of the star's material
blows off as a planetary nebula, gently moving away from the remnant core
Stars that do not have what it takes to succeed as a star (i.e. do not have enough mass to fuse hydrogen into helium at their centers) are called
brown dwarfs
Really massive stars differ from stars with masses like the Sun in that they
can fuse elements beyond carbon and oxygen in their hot central regions
Which of the following is a characteristic of degenerate matter in a neutron star?
electrons and protons join together in the nucleus to make neutrons and neutrinos
As the core of a high-mass star is becoming a neutron star or a black hole, the rest of the star's material
explodes outward as a supernova, rapidly moving away from the remnant core
What is the name of the process where a nucleus is split up into smaller nuclei or particles by forcing it apart?
fission
Astronomers identify the main sequence on the H-R diagram with what activity in the course of a star's life?
fusing hydrogen into helium in their cores
What is the name of the process where nuclei or particles are slammed together in order to make a new nucleus?
fusion
Is the neutrino involved in any of the proton-proton chain ("pp chain") fusion reactions?
it is an ending product in step 1
Measurements show a certain star has a very high luminosity (100,000 times the Sun's) while its temperature is quite cool (3500° K). How can this be?
it must be quite large in size
What happens to the positron created during the p-p chain of nuclear reactions inside the Sun?
it quickly meets an electron and both annihilate one another, emitting pure energy in the form of a gamma- ray photon
If you trace back the history of a carbon atom in your little finger through all of cosmic history, where did this atom most likely originate?
it was fused from 3 helium nuclei in the core of a red giant star long before the Sun existed
How long a main sequence star remains on the main sequence in the H-R diagram depends most strongly on
its mass
The most common kinds of stars in the Galaxy have
low luminosity compared to the Sun
Stars on the main sequence obey a mass-luminosity relation. According to this relation,
luminosity is proportional to mass to the fourth power (luminosity increases strongly with mass)
Stars that lie in different places on the main sequence of the H-R diagram differ from each other mainly by having different
masses
Which of the following statements comparing a neutron to a neutrino is FALSE?
neutrons are harmless to humans, whereas neutrinos are dangerous
Which of the stars with the following spectral classes will most likely leave behind a black hole after it goes supernova?
O
What are the spectral classes of stars?
O B A F G K M
Biologists tell us that life on Earth took billions of years to evolve into astronomy students and other examples of intelligent life. If we want to search for planets with intelligent life-forms that evolved over the same period of time that we did, what sorts of stars should we not bother searching around?
O and B type stars
What is the mnemonic that is used for remembering these spectral classes?
Oh Be A Fine Guy/Gal Kiss Me
Which of the following statements is FALSE about pulsars?
Pulsars were first detected at optical wavelengths
Is it involved in any of the proton-proton chain ("p-p chain") fusion reactions?
- it is a starting product in step 2 - it is an ending product in step 1
Which of the following statements comparing a neutron to a neutrino is true?
- neutrons are much heavier than neutrinos; neutrinos have such a low mass that they were once believed to be mass-less - neutrons interact with other matter all of the time, whereas neutrinos very rarely interact with other matter - both neutrons and neutrinos have no charge - neutrons are an important component of the atomic nucleus, whereas neutrinos are not
What are the sub-classes? Please explain how these work relative to the classes above
-0-9 -sub A class: A0, A1, A2, A3....., A9 -Temperature decreases as you move from 0 to 9, meaning an A0 star is the hottest A class star and an A9 star is the coolest A class star
Based on the mass that each of these stars are born with, select the most probable final state of their remnant core:
-0.2 solar masses: white dwarf -0.5 solar masses: white dwarf -1 solar masses: white dwarf -1.5 solar masses: white dwarf -2 solar masses: white dwarf -2.5 solar masses: white dwarf -5 solar masses: white dwarf -8 solar masses: white dwarf -12 solar masses: neutron star -50 solar masses: black hole -100 solar masses: black hole
Based on the final mass that each of these stars has, just before ending their life, select the most probable final state of their remnant core:
-0.2 solar masses: white dwarf -0.5 solar masses: white dwarf -1 solar masses: white dwarf -1.5 solar masses: neutron star -2 solar masses: neutron star -2.5 solar masses: neutron star -5 solar masses: black hole -8 solar masses: black hole -12 solar masses: black hole -50 solar masses: black hole -100 solar masses:
What is the mnemonic that is tacked onto the end of the mnemonic that you wrote down in part b that includes the three spectral classes for brown dwarfs?
-Lets talk, yo -Lats talk, you
Which of the following stages will our own Sun go through in the future?
-giving off a planetary nebula -expanding to become red giant -spending a long time on the main sequence -eventually fusing helium into carbon
1) The maximum mass that a white dwarf can have and still be able to support itself via electron degeneracy pressure is 2) This maximum mass is referred to as the
1) 1.4 solar masses 2) Chandrasekhar limit
1) About how long does it take a photon, once formed within the core of our Sun, to make its way out to the surface? 2) About how long does it take a neutrino, once formed within the core of our Sun, to make its way out to the surface?
1) >100,000 years 2) 2 seconds
1) If the white dwarf in this photo (before stealing matter from the red giant) has a mass identical to our Sun's mass, what will happen when 0.3 solar masses of the red giant star becomes accreted onto the white dwarf (i.e., falls onto the white dwarf and becomes part of its mass)? 2) If the white dwarf in this photo (before stealing matter from the red giant) has a mass 1.3 times the mass of our Sun, what will happen when 0.3 solar masses of the red giant star become accreted onto the white dwarf (i.e., falls onto the white dwarf and becomes part of its mass)?
1) a nova is possible 2) a white dwarf explosion supernova is possible
1) What is the isotope of Hydrogen that we call "Heavy Hydrogen"? 2) How many protons does this "Heavy Hydrogen" nucleus have? 3) How many neutrons does this "Heavy Hydrogen" nucleus have?
1) deuterium 2) 1 3) 1
1) star with the smallest radius? 2) star with the largest radius?
1) neutron star 2) red supergiant
1) the strongest of the four forces 2) the weakest of the the four forces 3) which force has the shortest range? 4) what is the force responsible for nuclear fusion? 5) what is the force responsible for nuclear fission?
1) strong nuclear force 2) gravity 3) strong nuclear force 4) weak nuclear force 5) strong nuclear force
1) The energy required to split a specific atomic nucleus is the same amount of energy that is released whenever that same atomic nucleus is formed 2) What name do we give to this energy?
1) true 2) binding
What are the spectral classes for Brown Dwarfs?
I, T, and Y
Fusion within the cores of massive stars can fuse up to (but not including) what element on the periodic table?
Iron
Which of the following types of stars will spend the longest time (the greatest number of years) on the main sequence?
K
