PHYS 1080 Exam 3


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How do astronomers on Earth use parallax to measure the distance to nearby stars?
As the Earth orbits the Sun, stars appear to change their position in the sky in relation to their background stars. Astronomers use parallax, the change in apparent position, to measure their distance. The greater the parallax, the closer a star is.
How is parallax measured (units)?
Parallax is measured using angles. 1 arcminute= 1/60th of a degree; 1 arcsecond=1/3600th of a degree. A parsec is the distance at which the parallax is equal to 1 arcsecond (3.26 light-years)
What is the difference between absolute and apparent magnitude? How is it measured?
Absolute magnitude is the measure of the intrinsic brightness of a celestial object, generally a star. Apparent magnitude is a measure of the apparent brightness of a celestial object, generally a star.
What is the difference between brightness and luminosity?
Brightness is how bright a star appears. Luminosity is the amount of light/energy the star emits from its surface.
What two factors affect a star's luminosity and how do they affect it?
Size- as the size increases the luminosity increases because the stars surface area is much greater
Temperature - a hotter and larger star is more luminous than a cooler star and smaller star
What is the ground state of an atom? The excited state?
The ground state is the lowest possible energy state, excited states are any states above the ground state.
When do atoms emit photons? Briefly describe the process.
An atom emits a photon when it goes from the excited state and loses its energy. An electron can gain energy in the ground state and move up energy levels, when it gets to the excited state its starts to lose energy and that losing of energy is emitting a photon or the process of emission.
What does an emission spectrum look like and how is it formed?
An emissions spectrum looks like a set of colorful lines within a black background. It is formed by electrons that are excited therefore having a higher state and as the state falls they create energy. This energy is photons, hot gas is where you are going to get the emission spectrum
What does an absorption spectrum look like and how is it formed?
An absorption spectrum is a rainbow with black lines, the opposite of what an emission spectrum looks like. The way it is formed is an electron absorbs the energy of a photon to jump to a high energy level leaving behind a black absorption line.
Why do astronomers consider the spectrum of a star so important?
Fingerprint for the star, elements, characteristics of said star.
What quantity is the spectral class of a star related to? List the spectral classes of stars in the order of decreasing temperature (from hottest to coolest).
The spectral class of a star is related to its temperature. In order of decreasing temperature; OBAFGKM.
What does Wien's law tell us?
Wien's Law tells us that objects of different temperature emit spectra that peak at different wavelengths. Hotter objects emit most of their radiation at shorter wavelengths; hence they will appear to be bluer. Cooler objects appear more red.
What two variables are plotted on the H-R diagram? What 3rd characteristic can you determine from a star's location on the H-R diagram?
The variable on the x-axis is surface temperature in kelvin, increasing from right to left. The variable on the y-axis is luminosity relative to the sun. The 3rd characteristic that can be determined is the star's radius relative to the sun, with the bottom left being the smallest and the top right being the biggest.
Where are the largest stars located? The smallest stars? Where are the hottest main-sequence stars located? The coolest?
The largest stars -supergiants- are located in the top right corner of the diagram, while the smallest stars -white dwarfs- are at the bottom left corner. The hottest main-sequence stars are towards the top left of the diagram, and the coolest are towards the bottom right.
In what group are most of the stars located? What does this imply?
Main sequence. This implies that most stars spend their lifetime there and become adult stars.
What is nuclear fusion?
Coming together
Where does nuclear fusion occur in the Sun and why?
Nuclear fusion occurs in the core of the sun because it is hot and dense enough for fusion to occur
Where does the energy come from that is generated in the proton-proton chain?
Proton-proton chain: 4 hydrogen nuclei turn into 1 helium nucleus, plus neutrinos and energy
Mass of 4 H nuclei is greater than 1 He nucleus
What is hydrostatic equilibrium?
A star is in hydrostatic equilibrium when the outward pressure is equal to the inward force of gravity at every point in the star
Briefly describe how energy is transported from the core of the Sun to the surface of the Sun.
-First, energy goes through the radiation zone which are layers right outside the core. The photons are traveling from hotter to cooler energy.
-Second, energy goes through convection zone which is the layer in between the radiation zone and surface. Also where gas rises or falls depending on temperature. Hot gas /rises and Cool gas/falls(Photons take 100,000 years to get to surface)
(EXTRA)Third, Neutrinos produced in core from the development of Deuterium and only takes few seconds to get to surface
What are neutrinos and why are they important?
Neutrinos are a nearly massless particle. A proton and neutron emit Neutrinos in the core and are the creation of Deuterium, neutrinos take only a few seconds to get from core to surface and scientist use them to detect nuclear fusion in the core.
Describe the three layers that make up the Sun's atmosphere.
The three layers of the sun's atmosphere are the photosphere, chromosphere and corona. The lowest layer is the photosphere which is where the sun's energy is released as light (considered the surface of the sun). The chromosphere emits a red glow as hydrogen burns off. The Corona is the hottest layer and it extends very far out (so hot it emits x rays that we can detect).
What is helioseismology?
Sound waves that move through the sun, making surface and interior waves.
What is solar wind?
the continuous flow of charged particles from the sun that permeates the solar system; charged particles flowing away from the Sun along magnetic field lines leaving through coronal holes
Define/describe sunspots, prominences, solar flares.
Sunspots- Cooler areas in the photosphere, the structure is the dark umbra surrounded by penumbra and it is caused by solar magnetic field
Prominences- Hot rising gas in the chromosphere (due to magnetic field)
Solar Flares- They are more energetic than prominences (due to magnetic field)
What is the length of a sunspot cycle? What is the length of the solar magnetic cycle?
The length of a sunspot cycle is 11 years. The length of the solar magnetic cycle is twice as long, 22 years. Magnetic field flips every 11 years and that is what is associated with the sunspots.
What are some of the effects of solar activity on the Earth?
UV and X RAYS heat up the earth's surface. Solar storms can occur from that causing Aviation and satellite damage and blackouts. Also because of solar activity it allows us to see auroras.
Which stars are considered low-mass stars?
A star is considered to be a "low mass" star if the mass of the star is less then 8x (Eight times) the mass of the Sun. The "Low Mass" Stars are found in the lower right corner of the main sequence section of the H-R Diagram.
What factor is most important in determining a star's position on the main-sequence and its subsequent evolution? Why?
It depends on the stars mass. The higher the mass of the main-sequence star the shorter its life is because with it being so big, energy has to burn so much faster to keep the star stable. With it having a higher mass and shorter life it goes through cycles faster of supergiant then explode. Low-mass stars have a longer life so they take a lot longer for evolution.
Describe the relationship between gravity and gas pressure when a star depletes the supply of hydrogen in its core. What happens to the size of the core?
Gravity and pressure have to stay balanced. If the one is too high the star can explode or collapse. When Hydrogen finally stops fusing the core gets smaller because temperature and pressure decreases.
What is degenerate matter?
Degenerate matter (very dense, small and non fusing). There's not enough thermal pressure to resist and balance gravity so the helium core becomes degenerate matter, which is very dense and smaller. Degenerate means non-fusing.
What is the next step in a star's life when it exhausts the hydrogen in its core? Is anything fusing in the core? In shells around the core?
The next step is the star leaves the main sequence and becomes a red giant. Nothing is fusing in the core because it is degenerate, but hydrogen starts fusing in the shells around the core.
What happens to the luminosity and temperature of a low-mass star when it becomes a red giant? Why?
The temperature decreases and the luminosity increases because the bigger the bright it is and due to all layers the heat decreases.
What is the helium flash?
A very brief thermal runaway nuclear fusion of large quantities of helium into carbon through the triple-alpha process in the core of low mass stars.
What is the next step in a star's life after the helium flash? Is anything fusing in the core? In shells around the core?
The core quickly heats up and expands. Helium fuses to carbon in the core, while the hydrogen fuses to helium in a shell around the core, starts expanding again.Horizontal Branch
Describe what is happening to the star when it is on the asymptotic giant branch? Is anything fusing in the core? In shells around the core?
When a star is in the asymptotic giant branch, helium is depleted in the core, and hydrogen and helium fusion continues in shells around the non-fusing carbon core. The star increases in luminosity, and the outer layers expand and cool.
What is a planetary nebula?
A ring-shaped cloud of gas and dust formed by an expanding shell of gas around an aging star. It's created when a star blows off its outer layers after it has run out of fuel to burn. These outer layers of gas expand into space, forming a nebula.
What is a white dwarf?
Leftover core of star remains as white dwarf. Masses 0.6-1.4 Mo, size like Earth. Hot, but not very luminous due to small size (only has non-fusing carbon core). Cool off because no nuclear fusion is occurring.
What is the correct order of evolutionary stages for a solar mass star? Be able to identify them on a H-R diagram.
main sequence, red giant branch, helium flash, horizontal branch, asymptotic branch, planetary nebula, white dwarf
What is a star cluster? How can you determine the age of stars in a cluster?
A star cluster is simply a group of stars that you can determine the age of by determining the age of the main sequence turnoff stars. Basically, the star cluster age equals the main sequence lifetime of the turnoff stars.
How does a nova occur?
A nova occurs when the white dwarf steals gas from its nearby companion star. Through binary system. Becomes so hot that explosion happens at the surface.
When does a Type Ia supernova occur?
Occurs when the stars are in a binary system, when two stars are orbiting each other, and one must be a white dwarf
Why do higher mass stars live shorter lives on the main sequence than lower mass stars?
Lower mass stars live longer lives because higher mass stars burn through their nuclear fuel faster.
What is the CNO cycle in high-mass stars?
-is one of the two known sets of fusion reactions by which stars convert hydrogen to helium, the other being the proton-proton chain reaction. Unlike the latter, the CNO cycle is a catalytic cycle. It is dominant in stars that are more than 1.3 times as massive as the Sun.
-is powered by fusion of hydrogen into helium in its core. Fusion is stabilized by a natural pressure-temperature thermostat.
What is the instability strip?
The instability strip is what stars can pass through on the H-R diagram as they expand and cool. It contains Cephis variables (high-mass stars) and RR Lyrae variables (low-mass stars).
Why are Cepheid variable stars important?
Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use Cepheids as "standard candles" for distance measurements.
What does the onion structure of a high mass refer to? How long does the fusion of each layer take?
The onion structure is all the elements smaller than iron that a high mass star burns through because the core is so hot and since the pressure and temperature are so high it lives a shorter life which means fusion rates are fast. As the star is fusing it is using heavier and heavier elements causing the onion-like structure.
Why doesn't a core made of iron support a massive main-sequence star?
Iron fusion does not create energy; it consumes energy and is thus cannot sustain a star. A high mass star will only fuse elements up to iron, then the iron core will collapse.
When does a Type II supernova occur?
Outer layers of a star blow off in tremendous explosions, the light emitted being equivalent to a billion Suns. A star must have 8-50 times more mass than the Sun to occur. Also because Iron stops fusing
Why will a neutron star form when the core of a massive star collapses?
Gravity has the upper hand and forced electrons into protons producing neutrons. The core contracts until neutrons are filled tightly as the rules of quantum mechanics allow; it is because of neutron-degenerate matter
What are the characteristics of a neutron star?
They are pretty small about the size of a city (1.4 - 3x the mass of the sun)
What are pulsars?
Pulsars are rapidly rotating neutron stars that consist of a combination of strong magnetic fields and rapid rotation leading to a beam of radiation that sweeps around like a lighthouse beam.