Study Guide part 2
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- Know the minimum temperature carbon will fuse at
- 600 million K.
- Know what the heaviest element that can be produced by nuclear fusion is
- Iron.
- Know that fusion of elements heavier than carbon occur in massive stars
- Yes.
- Know what causes a type II supernova explosion and that its spectra has strong hydrogen lines
- Have spectra rich in hydrogen lines, produced by collapse of a massive star with an iron core.
- Know why carbon cannot fuse in stars within this size range
- They do not get hotter than 600 million K, so carbon - oxygen core is the final stage.
- Predicted radius and density of a neutron star
- Radius is 10 KM, density is 10(14th) g/cm(3).
- What is the density of hot, low density clouds
- One tenth atoms / cm3.
- Know that the Crab Nebula confirmed pulsars are neutron stars and how It confirmed it
- It confirmed it by emitting consistent radio signals.
- What are bipolar flows and what do they cause
- Matter flowing into a protostars swirls through a thick disk and by a process believed to involve magnetic fields.
- Know the correlation between the mass and lifetime of a star
- More massive shorter life.
- Know which direction star moves on HR diagram as it enters red giant stage
- Up and to the right. Know the two properties of degenerate matter that are important in stellar evolution? Resists compression and pressure does not depend on temperature.
- What are Bok Globules
- Dense, dusty clouds, 1 ly in diameter, 10 to 1000 solar maseses, most are cold at their centers. What are Herbig-Haro objects? Small nebulae that fluctuate in brightness, produced by flickering jets from newborn stars exciting the interstellar medium.
- What are star clusters and associations
- Cluster remain together through time, associations drift away with time.
- What is the stellar model of our sun (ie how its interior is believed to be arranged in terms of radiation and convection)
- Arranged with a Radioactive Core and a convective outer envelope.
- Know what black dwarfs are
- White Dwarfs after they have radiated all of their heat after billions of years.
- What is the definition of the birth line on the HR diagram
- Shows where contracting protostars first become visible.
- What is the infrared cirrus and why is it highly luminous at low temperatures
- Cool gas with a large surface area.
- Know the two reasons why there is such an abundance of low-mass stars
- Long life times and high frequency.
- What is the Pressure-Temperature thermostat concept
- A natural regulation system, core gets hotter and pushes out.
- What are molecular clouds
- 10 to third to 10 to the fifth atoms/cm3, temp as low as 10k, mass of a few thousand to a few million solar masses, detected by CO radio emissions.
- Know the two reasons why each heavier element provides less fuel for nuclear fusion
- Less energy per reaction, less atoms available for reactions.
- What does the law of hydrostatic equilibrium implies
- Higher pressure = higher density and temperature.
- Know what the density and chemical composition of a white dwarf is
- Density is 3X10(6th), crystals of carbon and oxygen.
- What are the four quantities stellar models produce
- Temperature, mass, density, and energy flow.
- Know the definition of the term "compact object"
- Matter is in a degenerate state.
- How absorption spectra of stars and Doppler broadening are used to analyze what is in the interstellar medium
- Look for narrow absorption lines to find interstellar medium gasses, narrower to find stars.
- What is the connection between the mass of the protostars and the time it takes to become a main sequence star
- More massive stars contract more quickly.
- What is opacity and how it effects energy transport in a star
- The gasses resistance to the flow of radiation.
- Know maximum mass a red dwarf can be
- Less than (point) 4 solar masses.
- What are the four laws that determine stellar structure
- Laws of mass and energy, Hydrostatic equilibrium, energy transport, stellar models.
- Know what the Chandrasekhar limit is
- Know what a pulsar is? Know that pulsars were almost called "LGM" and what that stands for? Know what nebula was used to make the connection between neutron stars and pulsars? Know that the lighthouse model is the model that explains how neutron stars create pulsars? Know the definition of "escape velocity"? Be familiar with the theoretical prediction of what a black hole is and how it is connected to escape velocity and the speed of light? Know the definitions of "singularity" and "event horizon"? Know what the definition of the Schwarzschild radius is? Know what the radius of the earth would have to be for it to become a black hole? Know minimum core mass required to create black hole? Know what properties a Schwarzschild black hole has? Be familiar with the effects near a black hole: time dilation, gravitational redshift, tidal forces? Know what observational clues astronomers look for when trying to find a black hole? Know the definition of variable stars and the periods of the two types? Know how Cepheid variables were used by Harlow Shapley to discover the center of the galaxy? Understand the period - luminosity relation? Know the definition of "open clusters" and "Globular Clusters" and how shapely found they were distributed throughout the galaxy? Know the definition of proper motion, transverse velocity, and radial velocity? Know the distance of our solar system from he center of the galaxy in kpc (kiloparsecs), and the diameter of the galaxy in light-years? Know the general properties of the disk and spherical components of the galaxy? Understand the process by which 21-cm radiation is created in cold neutral hydrogen clouds? Know the orbital speed of the solar system around the center of the galaxy, the period of revolution, and what the lower limit for the mass of the galaxy is? Know what "Keplerian Motion" and "rotation curves" are , and what the rotation curves for the stars in the outer part of our galaxy suggest? Know the definition of "dark halo" and galactic corona"? Know age range of open clusters in the disk componet and the average and oldest ages of globular clusters in the spherical component? Know the definitions of population I and II stars and where each is located? Know the definition of the element-building cycle given in the class notes? Know what the traditional hypothesis of the beginning of the milky way galaxy is, its two drawbacks, and their solutions?
- Know how a star's position on the HR diagram changes over time
- Upward and slightly to the right.
- Know that the supernova SN1987A confirmed iron core collapse theory of type II supernova, and know how it confirmed it
- Neutrino blast 4 hours before detected visually in large magellanic cloud.
- Know what white dwarfs are
- The remains of medium mass stars.
- Know the cause of a type I supernova explosion and its spectra has no hydrogen lines
- Produced by the collapsing white dwarf
- Know why medium mass stars swell into red giants
- They ignite helium and hydrogen.
- What is the effect of a free-fall contraction on the core of a protostars
- It is warmed which slows contraction.
- What is the CNO cycle, what temperature it is efficient at, and the lower mass limit of stars it dominates in
- Carbon-Nitrogen-Oxygen cycle, 16 million K, greater than 1.1 solar masses.
- Be familiar with the process of how and why stars expand into giants in the last 10% of their lifecycle explained in the text and class
- Helium accumulates at core, helium core converts gravitational energy to heat and ignites surrounding shell of hydrogen, hydrogen fusion shell expands outward and swells the star into a red giant.
- Know two advantages that give red dwarfs a longer lifespan
- Pressure-temperature thermostat set low, core is thoroughly mixed.
- What causes Neutron stars and its three predicted properties
- Hot surface, Rapid Spin, Powerful Magnetic Field.
- Reflection nebula are
- Light is reflected by dust grains in colud.
- What are T Tauri stars
- Stars just visible, brand new stars, just crossed the birth line.
- Emission nebula are
- Ionized gas due to nearby hot stars.
- Know what a helium flash is and under what conditions it occurs
- when helium gas becomes degenerate before reaching 100 million Kelvin in stars greater than (point) 4 solar masses but less then 3 solar masses.
- Understand why the mass - luminosity relation exists (ie the connection between pressure, temperature, and energy production)
- The more massive a star is, the more luminous it is, Higher pressure means higher temp.
- Do red dwarfs ever enter giant stage
- No
- Know how much more luminous a type I supernova is than a type II supernova
- Type I is 6 times more luminous than type II.
- What does the triple-alpha process produce and the minimum temperature it occurs at
- Heavy element fusion (helium to Be to Carbon) 600 million K.
- What type of information on the interstellar medium x-rays, ultraviolet, and radio waves yield
- X-rays yield very hot gases due to exploding stars, Ultraviolet yield distribution, composition, and temperature of gas, Radio yield specific molecules in giant molecular clouds.
- Know the mass range of medium mass stars
- (point) 4 to 4 solar masses.
- Know what planetary nebulae are
- The outer envelope gasses expelled by a dying star, glow due to ionization from hot core.
- Know what a neutron star is
- 1 solar mass compressed to a radius of about 10 Km.
- What is "Doppler Broadening
- Hotter gasses yield broader spectral lines.
- Know the minimum temperature helium fuses at
- 100 million K.
- What are the three types of energy transport and which one are important in stars
- Conduction, (convection, radiation).
- What are the four ways that star producing shock waves are produced
- Supernova explosions, birth of very hot (o and b) stars, cloud collisions, spiral arms of galaxy.
- What is interstellar reddening
- Shorter wavelengths are scattered more easily than longer wavelengths, the redder photons are more likely to make it through the cloud.
- What is a protostars and what are the steps in which it becomes a star
- An object that will eventually become a star, center is warmed slowing contraction, hydrogen fusion begins, gas and dust blown away.
- Know the definition and upper mass limit of a brown dwarf
- Less than point 08 solar masses.
- Know why the gas remnants of a supernova keep glowing for a long time after the explosion
- Presence of radioactive nuclei such as nickel - 56, which means fusion of elements with a higher atomic number than iron occurred in supernova explosion.