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76 Cards in this Set
- Front
- Back
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From the center outward, list the layers of the sun in the correct order
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Core, radiation zone, convection zone, photosphere, corona
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Two stars, Freddy and Barney, are the same size. Fred has the spectral type F; Barney has B. Which is more luminous and why?
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Barney is more luminous bec spectral type B is more luminous than F
More -> less Spectral types: O B A F G K M L T |
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A 10 solar mass star is more than ten times more luminous than a 1 SM star?
True or False? |
True.
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Where does light come from?
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Accelerating charges produce light- electromagnetic radiation
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Transverse Waves
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Displacement is perpendicular to the direction of the motion of the wave.
EX: light Obeys equation c = λf, where λ is the wavelength, f is the frequency, and c is the velocity (speed of light) |
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What is diffraction?
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The bending of light around an obstacle
Proven by young's double slit experiment |
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What is a photon?
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The energy of a particle of light
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An atom consists of:
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An atom consists of a small, dense nucleus (containing protons and neutrons) surrounded by electrons
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So if a nucleus the size of an orange (10 cm) was located at the center of Yankee Stadium, where would the electron be?
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Rockafellar center
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Photons (lightwaves) are emitted from an atom when
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an electron moves from a higher energy level to a lower energy level
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Photons can be absorbed by an atom when
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an electron moves from a lower energy level to a higher energy level
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Each chemical element produces...
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its own unique set of spectral lines when excited
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Continuous spectrum
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Law #1- The excited atoms within a hot dense object give off light of all colors (wavelengths) and produce a continuous spectrum -- a complete rainbow of colors (range of wavelengths) without any spectral lines
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Emission line spectrum
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Law #2 – The excited atoms within a hot, cloud of gas give off only particular colors (wavelengths) of light and produce an emission line spectrum - a series of bright spectral lines against a dark background.
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Absorption line spectrum
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Law #3 – When the light from a hot dense object passes through a cool cloud of gas, the atoms within the cloud can absorb particular colors (wavelengths) of light and produce a absorption line spectrum - a series of dark spectral lines among the colors of the rainbow.
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What physical situation does a star like the sun present?
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A hot dense core surrounded by a low density outer atmosphere
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What spectra are stars?
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All stars produce dark line absorption spectra
(tutorial; light & atoms) |
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What happens when you put all of the colors or light together?
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White
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If you pass white light through a prism,
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it separates it into its components
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What can we learn by analyzing starlight?
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A star's temperature
A star's chemical composition |
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Black body curve
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A graph of an object's energy output vs. wavelength
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Peak wavelength of a blackbody curve tells us
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about the object's temp and color
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The longer the peak blackbody wavelength,
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The cooler (redder) the temp
[shorter bluer, hotter] |
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Stefan-Boltzmann Law
Thermal Radiation Law 1 |
Emitted power (per square meter of surface)
= sigma T ^ 4 where (Greek letter sigma) is a constant with a measured value of = 5.7 x 10-8 watt/m2 x K4) and T is one the Kelvin scale (K). |
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Wien’s law
Thermal Radiation Law 2 |
Relates the temperature of an object to the wavelength of the peak in the blackbody curve.
λpeak = (2.9 x 106)nm / Tkelvin The higher the object’s temperature, the shorter the wavelength of the peak for the light emitted by the object. |
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What color is our sun
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The Sun emits all wavelengths of electromagnetic radiation (light); however, the wavelength of light it emits most intensely is in the green part of the spectrum.
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Tutorial
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Blackbody radiation pg 57
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Short- long wavelength
7 parts of the electromagnetic specta are: |
gamma rays, x-rays, UV rays, visible (sight), infrared, microwaves, and radio - long wavelengths.
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How does the sun shine?
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High temp allows nuclear fusion to happen at the core.
Neutrinos created during fusion fly directly through the Sun This excess mass becomes energy. That is ~ 0.7% of the original Hydrogen mass is converted into energy during the Hydrogen fusion. This mass becomes energy according to E = mc2. Energy gradually leaks out of radiation zone in form of randomly bouncing photons |
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the order of magnitude of stars (1st mag, 2nd mag, etc.)
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Is the order in which they become visible as our sun sets
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Apparent magnitude
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how bright an object appears from earth
-denoted by letter 'm' -the larger the number, the dimmer the object |
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absolute magnitude
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how bright the star actually is, its intrinsic brightness
-denoted by 'M' -compares the brightness of all the stars as if they were all the same distance away from Earth, 10 pc gives a number that indicates the actual brightness or luminosity of the star. |
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Inverse square law
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Apparent brightness also decreases as 1/ r^2
so as distance doubles: brightness is decreased by 1/4 distance halves: brightness increases by 4 times |
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How do we determine the absolute magnitude of a star?
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We imagine having them all lined up together at the same distance (10 parsecs or 32 light years), then compare the brightness of each star
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How can we estimate a star's distance from earth based on its two magnitudes?
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When m = M, then the star is located exactly 10 pc away
When m<M, then the star appears brighter than it would if it were 10 pc away so it must be closer than 10 pc When m>M, then the star appears dimmer than it would if it were 10 pc away so it must be farther than 10pc |
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Aparent and absolute magnitude lecture titurial
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p 33
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Where do stars come from & why
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Stars condense from clouds of gas and dust that exist throughout the disk of the galaxy
Step 1.) Gas/dust cloud collapses =>the center becomes very very hot and very very dense Step 2.) Fusion =>As the gas cloud collapses due to gravitational forces, the core becomes hotter and denser, Eventually, reaching a point where nuclear fusion can occur Step 3.) Balance =>Fusion produces radiation (light) that creates an outward pressure. During hydrostatic equilibrium a balance between the gravitational collapse of the star pushing inward and the outward pressure produced by photons from nuclear fusion in the core. |
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What is the significance of the main sequence?
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All Main Sequence stars are in hydrostatic equilibrium because nuclear fusion of hydrogen is producing enough outward pressure to balance gravitational collapse
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Stars spend most of their life time as:
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A main sequence star-
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Binary stars
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when stars form in pairs. These stars can orbit each other much like a star and a planet, and in some cases the stars pass in front of each other - we call these “Eclipsing Binary” stars
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Stars leave the main sequence
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The hydrogen atoms in the core of the star that fuse together to create helium, start to run out and fusion begins to slow down
The system becomes out of balance Something has to happen to keep the star from collapsing in on itself |
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When core hydrogen fusion ceases,
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a main-sequence star becomes a giant.
, the star will collapse inward – this causes the layer just outside the core to become so hot and dense that hydrogen fusion will begin in this outer layer. The energy produced by hydrogen fusion in this layer just outside the core causes the rest of the star to expand into a giant star. Stellar burp! |
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As main sequence stars become red giants
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They increase in luminosity and brightness and decrease in temp
helium fusion happens in the core |
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What happens after the red giant stage in a low mass star?
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The core runs out of fuel!
Shell fusion begins outside the core. Eventually the process shell fusion creates too much outward pressure and energy which explosively pushes out the outer layers of the star and produce a planetary nebula. |
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The burned out core of a low mass star becomes a
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White dwarf
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What is a nova?
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A nova occurs in binary systems where a white dwarf is pulling mass from its companion.
A nova is a relatively gentle explosion of hydrogen gas on the surface of a white dwarf in a binary star system. This process does not damage the white dwarf and it can repeat. |
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What is the fate of our sun?
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Since the Sun has a mass less than 8 M and since it is alone without a companion, it will become a White Dwarf and then slowly cool into a Black Dwarf
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What are the stages of a high-mass star?
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A series of different types of fusion reactions occur in high-mass stars
The core and outer layers run out of fuel. The star then collapses, due to gravity. The mass, however, is high enough that nothing can balance the gravitational collapse and….. Supernova type II Interstellar cloud-> Big main sequence star -> Super red giant ->Type II supernova |
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Supernova type II
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The collapsing outer layers of the star will collapse inward and bounce outward off the compact collapsed core in an explosive event sending out a shockwave. This explosive event is called a Type II Supernova!!!
During the Supernova, heavier elements are created from fusion events, like magnesium, lead, or gold. |
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"we are all made of star stuff"
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The atoms that created our world and solar system come from nuclear fusion in stars and from Supernovae events!
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Neutron star
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A core with remaining mass of 1.4 to 3 M, composed of tightly packed neutrons.
These tiny stars are much smaller than planet Earth -- in fact, they are about the diameter of a large city (~20 km). One cubic centimeter (like a sugar cube) of a neutron star, would have a mass of about 1011 kg! (hundreds of billions of pounds!) A paper clip of a neutron star is equivalent to the weight of Mt. Everest! |
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Black Holes
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A black hole is a collapsed stellar core. It is a location in space of enormous gravitational attraction. The gravitational attraction is so strong that photons of light can not even escape (that’s why it’s black)!
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High mass stars life time
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Interstellar cloud -> Big main sequence star -> Super red giant -> type 2 supernova
from type II supernova either black hole or neutron star |
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Which will have a greater core temperature and density – a high mass star or a low mass star?
Which will then have a greater fusion rate? Which will use up its fuel more quickly? What is the fuel? |
Consider a main sequence star with 10 times the mass of the Sun
It will: have higher temps and pressures at the core have greater fusion rates - consumes fuel at 1000 times the rate of the sun be 1000 times as bright and last 1/100 as long “Burn bright, die young.” (Dr. J) |
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Timetimes of stars vs. size of the stars
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Bright O-type stars live very short lives (about 10 million years)
Very small stars live a long time (100 billions of years) Our SUN: will live a total of about 10 billion years (half used up) |
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Dark matter:
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An undetected form of mass that
emits little or no light but whose existence we infer from its gravitational influence |
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Dark energy:
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An unknown form of energy that
seems to be the source of a repulsive force causing the expansion of the universe to accelerate |
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Contents of the universe
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All other visible atoms: ~ 0.01%
Hydrogen and Helium ~ 0.50% Cold Dark Matter: ~ 25.00% Dark Energy ~ 70.00% |
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We can measure the velocities of galaxies in a cluster from their
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Doppler shifts
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Evidence for dark matter
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The mass we find from galaxy motions in a cluster is about
50 times larger than the mass in stars! also: Gravitational lensing, the bending of light rays by gravity, can also tell us a cluster’s mass |
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More evidence for dark matter
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Clusters contain large amounts of X-ray (light) emitting hot gas
Temperature of hot gas (particle motions) tells us cluster mass: 85% dark matter 13% hot gas 2% stars |
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What might dark matter be made of?
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Extraordinary Dark Matter (WIMPS)
Weakly Interacting Massive Particles: mysterious neutrino-like particles |
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Dark Matter in Galaxies
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We can apply Newton’s Law of Universal Gravitation and motion to obtain the orbital speeds of stars and gas clouds.
This data suggest that galaxies contain far more than what meets the eye (stars & glowing gas). |
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Dark Matter in Clusters
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We obtain evidence of dark matter by studying galaxy clusters.
Observations of galaxy motion (Zwicky’s data), hot gas, and gravitational lensing (Einstein) all suggest that galaxy clusters contain far more matter than we directly observe (stars and gas). |
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What are the largest structures in the universe?
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Galaxies appear to be distributed in gigantic chains and sheets that surround great voids
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What were conditions like in the early universe?
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The Universe is expanding
The redshifts of galaxies is evidence that the universe is expanding. |
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The Universe and Space Time
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Galaxies are moving away from us.
Galaxies that are further away are moving faster. The universe is expanding! The expansion of the Universe creates more space and time |
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Big bang
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is the event that marks the time when the universe began – the beginning of the expansion.
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All of the universe as we know it now, was once
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a single point-like location of infinite Temperature and Energy but was NOT composed of any Matter.
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Is there any evidence for the Big Bang?
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~380,000 years after the event of the Big Bang, the Universe cooled to a temperature of 3,000K, and light, which could not propagate until then, began to spread in all directions.
Working backwards, we should be able to see some evidence of this signature of light (blackbody radiation) at the time of the early universe. The light released then, almost 14 billion years ago, can still be observed now. The 3,000 Kelvin temperature of the early Universe has dropped to a temperature today of 2.735K (Blackbody peak in the microwave)-This is known as the Cosmic Microwave Background Radiation!!! |
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cosmic microwave background radiation
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Fills all space + is evidence for big bang.
The light released during the big bang, almost 14 billion years ago, can still be observed now. The 3,000 Kelvin temperature of the early Universe has dropped to a temperature today of 2.735K (Blackbody peak in the microwave) |
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The microwave background radiation is evidence to support the ideas that:
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The Universe was once much hotter, denser and smaller
There were times during the early universe when light could not freely travel through space. The Universe began during an event we call the Big Bang. The Universe is approximately 14 billion years old. |
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Does the universe have enough kinetic energy to escape its own gravitational pull?
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Fate of universe depends on the amount of dark matter
Amount of dark matter is ~25% of the critical density suggesting fate is eternal expansion But expansion appears to be speeding up! |
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What were conditions like in the early universe?
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The early universe was filled with radiation and elementary particles. It was so hot and dense energy could be matter and vice versa.
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What is the history of the universe according to the Big Bang Theory?
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There are eight eras: Planck, GUT, Inflation, Electro-weak, particle, nucleosynthesis, nuclei and atoms
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How does inflation explain the Big Bang?
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The origin of the density enhancements that turned into galaxies and larger structures
The overall smoothness of the universe on large scales The fact that the actual density of matter is close to the critical density |
