Final Exam Flashcards
What are the interior layers on the sun?
- Core: where energy is generated
- Radiation zone: radiation carries energy outward
- Convection zone: churning plasma carries energy outward
What is the photosphere
“Surface” layer of the sun that is visible to the human eye; includes sun spots and granulations in which the hot spots will bubble up to the surface, cool, and sink down into the convention zone
What are the outer layers of the sun
- Chromosphere: thin layer containing hot gas
- Corona: extremely hot and emits mainly x-rays
- Solar wind: layer not actually on the sun but surrounding it in which particles are expelled into
What makes it so that the sun doesn’t explode/implode?
Hydrostatic equilibrium created by the balance between gravity and pressure
What is the main source of the sun’s energy
Nuclear fussion
What elements is the sun mostly composed of
Hydrogen and helium
When nuclei fuse what happens to their mass
sum of fused nuclei is less than the sum of initial masses. Lost mass is converted to energy
How does the energy from the core reach the sun reach the surface and how long does it take?
Gamma rays slowly work their way out from the core to the surface, exchanging energy with the solar matter along the way, turning them into visible wavelenghts (radiative diffusion); takes hundreds of thousands of years
What evidence is there that the sun goes through radiative diffusion?
- Sunquakes: measurement of the movement of the sun’s surface using doppler shift of visible light shows oscillation spots that are congruent with sun spots
- 2 neutrinos from the core emergy for each helium fussion reaction but are very hard to detect. Can be detected using underwater experiments which show observations consistent with expectations from nuclear fission
what are the 7 primary types of stellar spectra from hottest to coldest and what are the subclasses of each class
O B A F G K M
Oh Be A Fine Guy, Kiss Me
from 0 - 9 where 0 is the hottest and 9 is the coldest
What is a brown dwarf
- Too cool/small to initiate p-p fusion
- Has a mass .075x smaller than the sun
- undergoes deuterium fusion; still generates energy
What are stars mostly composed of
Hydrogen and Helium; mostly H
Why are there typically narrow spectral lines for bigger stars
- broad spectral lines are due to a high number of particle collisions. Larger stars have a greater volume thus, low pressure meaning particles are less likely to collide with each other
- Gas is more likely to stay ionized when pressure is low thus, in large stars there are a lot of ionized atoms which have different spectra than neutral atoms
In the H-R diagram, what is the relationship between luminosity and size of stars for a given temperature
Higher the luminostiy, bigger the star
On the H-R diagram where are the 4 types of stars that are not on the main sequence
White dwarfs bottom left, red giants mid way up to the right, red super giants top right and toward the center, and blue giants somewhat bottom right of the main sequence line
What stars are on the main sequence of the H-R diagram
Stars fusing H in their cores
What are star clusters
Stars that all formed about the same time, born from giant clouds of gas
If a neutral dust/gas cloud is between us and a star what will the absorption lines look like
Absorption lines of the star’s surface will be broad due to high pressure, there will be additional narrower lines from the dust cloud, if the star is in binary there will be broad lines that move back and forth due to star oscillation of each other
What are the first 4 steps that a star goes through when getting off of the main sequence
- H core is exhausted
- Left w/ contracting He core
- Heat from contraction raises temp of H layer until it goes through fusion
- creates more energy resulting in layer expansion - Star becomes red giant
- He core contracts and heats up
- He flash results from rapid onset of He fusion
- He core expands and star contracts - Red giant stabilized as core goes through fusion
- Once He core is exhausted, goes into another core collapse with C and O
What happens to an initially low mass star after it goes through a C and O core collapse
- Gravitational potential energy ignited fusion of He shell
- He flash occurs and H shell ignites P-P fusion - Star expands into 2nd red giant phase
- Star goes from red giant to white dwarf
- In doing so, star ejects shells of gas which form planetary nebulae
- Remnant star is very hot and dense
What happens to an initially high mass star after it goes through a C and O core collapse
- Left w/ an iron core
- Takes energy - Star goes into supernova explosion
- Shells stop producing energy resulting in increase in mass
- Core contracts but is stopped by degenerate electrons
- Electron save core but sudden contraction stop causes rest of star to be blown apart - Star becomes neutron star or black hole
- Black hole if star was initially > 40x the sun
- Neutron star if star was initially 10-40x the sun
Explain what the Chandrasekhar limit is
White dwarfs shrink as the mass in the star increases
- As a star increases in mass, electrons become more tightly packed resulting in a smaller radius
- Theoretical models show that the maxiumum mass that a star can end its life with and still become a white dwarf is 1.4x the sun
What does the end of life look like for main sequence star in a binary system
- One becomes a red giant, dumping mass onto the other
- This star grows in size, becoming a red giant
- The two stars will exchange mass back and forth until one becomes a white dwarf
What is a cephid variable
large yellow star that is anywhere from 10^3-10^5 time as luminous as the sun
Why are cephid star’s useful
Can be used to determine the distacne to stars close to them. Find period of star to get luminosity, use that to get apparent brightness, and then use the inverse square law (1/r^2) to get distance
What is the relationship between magnitude and brightness
lower magnitude = brighter star
What are the products of p-p fusion cycle
4He nuclei, neutrinos, gamma rays and positrons
How long does it take initially high and initially low mass stars to reach their end of life and what do they become
Takes initially low mass stars ~100 million years to become white dwarfs. Initially high mass stars end up as neutron stars or black holes
Why do different stars have different spectral lines
They are all mostly made of H and He but they have different surface temperatures which affect the ionization states of different elements thus, there are different absorption lines for different elements
Why do larger stars stay on the main sequence for less time compared to smaller stars?
Bigger stars have a higher temperature thus, higher rate of fusion meaning they use up the H in their cores faster
What are the ways we can determine the masses of two stars in a visually binary system
- measure period and semi-major axis visually
- Use Kepler’s 3rd law to get M1 and M2
- Find location of center of mass, relative to either star giving M1 and M2
what are the ways astronomers use to identify binary systems despite the two stars not being close enough to see their separate images?
Spectral lines of binary systems show periodic variation in double absorption lines as doppler shift of each star varies in its orbit (red shift=decrease and away, blue shift = increase and towards).
Periodic dips in light curve when one star passes in front of the other
What is the white dwarf
Star with no nulear reactions going on in the core, which is primarily made of C and O
What is a protostar
Star of uniform composition from center to surface that contains H but has no others rxns going on in the core
Arrange the following in order of their evolution: white dwarf, protostar, main sequence, red giant: after He flash, and red giant: before He flash
Protostar, Main sequence, red giant: before He flash, red giant: after He flash, and white dwarf
The force needed to maintain a body at constant speed in outer space is equal to _____
Zero. Speed is constant so there is no acceleration thus, no force needed
