Lecture 11 - Our Star Flashcards
what are the 6 parts of the sun? and what happens in each
- solar core –> nuclear reactions, creates heat
- H and He gas but no nuclear reactions
- convection zone –> sends out energy via convection (hot gas rises, cool gas falls)
- photosphere –> visible surface of sun
- chromosphere –> middle layer of solar atmosphere, radiates most of sun’s UV light
- corona –> outer layer of solar atmosphere
how do nuclear reactions compare to chemical reactions?
nuclear reactions more efficient for producing energy
NUCLEAR FISSION
- what happens
- how does final mass compare to initial mass
- equation
- what happens to energy
- what is produced and why is this bad
- break atoms apart
- M > m+m
- M = m+m +energy
- energy released via E = mc2
- releases unstable radioactive nuclei –> dangerous if not handled properly
NUCLEAR FUSION
- what happens
- equation
- what happens to energy
- fuse 2 atoms together
- m+m = M + energy
- energy released via E = mc2
does the sun use nuclear fusion or fission? why?
FUSION
- sun has soup of hot gas with bare, positively charged atomic nuclei
- efficient and clean, no radioactive byproduct
is mass conserved in nuclear reactions?
YES
what is the 3rd type of nuclear reactions?
nuclear decay
describe the binding energy graph
energetically favourable to undergo FUSION of lighter elements to form iron –> increasing binding energy
energetically favourable to undergo FISSION of heavier elements to form iron –> decreasing binding energy
what is special about iron?
most stable element with lowest binding energy
why is it hard to start fusion on Earth?
requires A LOT of energy because light nuclei don’t know they prefer to be fused –> like charges repel so much have enough energy to push them together at high speed so nuclear force can take over
requires a lot of energy, but a lot is produced in return
why can the sun undergo fusion?
pressure, density, and heat at core of sun is large enough for nuclear fusion to occur easily —> overcomes energy requirement
what elements does the sun fuse? what is the process called and how does it work (3 steps)?
H fuses to He
via PP CHAIN
1. fuse 2 H protons to make DEUTERIUM (p+n)
2. deuterium interacts with another proton to make HELIUM 3 (p+p+n)
3. Two Helium 3 collide to form HELIUM 4 (p+p+p+n) and 2 extra protons
what is deuterium made of?
POSITRON –> antielectron
NEUTRON –> tiny mass
how much H is converted to He per second?
how long will it take for sun to run out of H?
4 million tons of H converted to He per second
takes 4 billion years to run out
what is released from fusion in the sun?
energy and radiation propagate outwards
light released (not particles) thru convective zone as heat
equation for release of energy from the sun
E = 0.007 (4m)c^2
4m = mass of 4 protons involved (6 protons enter, 2 protons leave)
energy difference btwn initial and starting products is 0.7%
how do you calculate # of atoms if sun was all hydrogen?
M_sun/M_Hatom
how do you calculate how much energy could be extracted from whole sun with pp chain?
E = mc^2
E = 0.007(# of atoms[10^57])mass of H*c^2
how do you determine how long the sun will last based on the watts it emits?
W = J/s
J/(J/s) =time
what would happen if the core temp increased? why does this happen?
high temp = more energy = more collisions = more fusion
higher core pressure exceeds gravity pressure so the core can expand and cools down
low temp = less energy = less collisions = less fusion
reaches gravitational equilibrium and energy balance is restored
BECAUSE SUN IS A SOLAR THERMOSTAT
3 pieces of evidence for standard solar model
- fusion is the only way that the sun could produce enough energy
- sun composition is mostly H (76% H and 22% He)
- we can detect neutrinos from sun
what do quarks form?
protons and neutrons
what are 2 particles that are similar to electrons?
muons and tau
what are neutrinos
produced due to fusion –> most abundant particles with mass in the universe
what is the solar neutrino problem?
HOMESTAKE mine detected too few neutrino reactions by a factor of 3
could solar model have been wrong? could the experiment have been wrong?
what was the solar neutrino solution? how did they solve the problem?
the solar model was correct but the homestake experiment only detected ELECTRON NEUTRINOS, which is only 1 type of neutrinos out of 3
SUDBURY NEUTRINO OBSERVATORY –> sensitive to all types of neutrinos
what is helioseismology?
studies oscillations of sun, vibrations of sun to see how heat works in the sun, internal movements and structure of sun
supports solar model very well
temperature of core, photosphere, chromosphere, corona
- CORE –> 15 million K
- PHOTOSPHERE –> 5700 K
- CHROMOSPHERE –> 10,000 K
- CORONA –> 1,000,000 K
describe the visibility of the photosphere
deepest visible region
density of gas is low enough (opacity is low enough) to let light leave from convection zone
(below photosphere, gas is dense and opaque)
how is light transported in the radiation zone?
energy transported upwards by photons
what is solar wind?
flow of charged particles from surface of sun into solar system
what is gravitational eqb?
sun wants to collapse under gravity but fusion energy exerts
what is energy balance of the sun?
rate at which energy radiates from the surface of the sun is EQUAL TO the rate at which energy is released by fusion
what is the purpose of gravitational contraction?
when did gravitational contraction stop?
provided energy that heated the core as the sun was forming
contraction stopped when fusion began
how can we detect the sun’s corona?
X-ray photos detect corona where magnetic fields trap hot gas
what is the role of the sun’s magnetic field?
allows for high core temperature
describe TRACE detection of magnetic field loops
UV light shows loops as highly ionized iron atoms traveling thru magnetic fields
what are sunspots?
what are they caused by?
what do they indicate?
dark regions in photosphere that are cooler than their surroundings
caused by magnetic fields that inhibit convection
only indicate temperature, they are not shadows!
what are solar flares? what are they caused by?
lots of high energy plasma escapes, allowing X-rays and charged particles to go into space
due to reconnection event of magnetic field lines in coronal holes
what leads to solar wind?
solar flares
what leads to auroras? why don’t they hit earth?
large mass ejections from solar flares
don’t hit earth bc of earth’s magnetic field
how do sunspots vary?
number of sunspots varies in 11-year cycle
what happens at the peak of solar cycle?
SOLAR MAXIMA
how long is the solar cycle?
22 years but the sun’s magnetic field flips every 11 years
