Test 2 for Stars the Galaxy and the Universe
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| The Main Sequence | EVERYTHING this test is about. Most stars are on the Main Sequence.dd
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| The more massive a star, the more... | luminous, larger, and hotter.
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| What determines the location of a star along the main sequence? | The Mass
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| Interstellar medium | What stars are made out of. Gas and dust between the stars. Most is gas; 1% is interstellar dust.
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| No stars less than about _____ have ever evolved off the main sequence. | 0.8M.
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| Fun facts about the gaseous portions of interstellar medium. | tenuous (1 atom per cubic centimeter). Gas emits various kinds of light, depending on its temperature.
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| Fun facts about the dust portions | solid grains, or "interstellar soot" (iron, silicon, carbon, and more). blocks visible light.
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| Size of interstellar dust | large molecules about 300nm
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| Interstellar reddening | Dust blocks short wavelengths more efficiently. Whilst long wavelengths such as infrared and radio waves penetrate dust.
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| Temperature of dust | typically cool (10-300K). Will emit infrared radiation.
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| Gas temperatures | ~10^6 K (very hot). Heated by shock waves from supernovae.
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| H II regions | T~10^4 K. Hydrogen heated and ionized by ultraviolet light from hot, luminous stars
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| Ionized | stripped of one or more electrons
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| Neutral Hydrogen Regions | Very cold. Hydrogen in single, neutral atoms, emits radio waves lamda=21nm. light penetrates the dust --> good for mapping the milky way.
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| Interstellar clouds | Includes most interstellar gas. Cool temperatures.
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| Intercloud gas | regions of hot gas which lies between interstellar clouds.
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| Molecular clouds | interstellar clouds which is cold enough for hydrogen to be in the H2 molecule. 120 light-years in size. Where stars form.
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| Temperature of Molecular clouds | 10K
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| Infrared vs Visible light view of the Milky Way | Light cannot escape the dark clouds, but dust absorption does not affect infrared light as much.
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| How stars form | Denser portions of the cloud collapse into star-forming cores. Rate of collapse is slowed by magnetic fields, turbulence and angular momentum but eventually, gravity wins.
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| cores. | Caused by collapsing molecular clouds.
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| Effect of angular momentum | Spin of the core produces a disk of material around the protostar. As more material is added, the speed of the cloud increases. Material is added perpendicular to the axis, not to the top/bottom, so a disk forms.
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| protostar | center of the star that is surrounded by large envelope of infalling gas and dust. Large, cool and luminous. emits infrared light.
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| Protostellar system | central protostar + disk + infalling envelope
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| Accreation Disk | Formed from the rotating cloud material.
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| The balancing Act that is protostar creation | As mass is added the interior is compressed and becomes hotter, pressure rises. gravity is balanced by the outward pressure force. thermal energy is radiated away and the protostar slowly shrinks.
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| Becoming a star | When the core becomes small enough and the temperature hot enough, hydrogen fusion begins and it becomes a main sequence star.
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| Temperature required for fusion | 10 million kelvin.
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| Mass required for hydrogen fusion | 0.08M. (Brown dwarfs)
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| Evolutionary track | Path of temperature and luminosity with time. Protostars of differeny masses follow different paths on their way to the main sequence.
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| Hayashi track |
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| Bipolar outflow | At the upper/bottom poles of a protostar. May be the result of magnetic interaction between disk and central protostar. Ejects lots of mass that would otherwise land on the star and disrupt the infall of material
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| Herbig-Haro objects | when powerful jets collide with interstellar medium
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| Star clusters | Gravitationally bound groups of stars
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| Time takes to form stars | May take millions of years. High-mass stars take less time to form and quickly evolve.
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| Hydrogen burning in low-mass M-S stars | p-p chain. proton-proton. fuses 4 hydrogen nuclei into 1 helium nucleus giving off radiation (positrons and neutrinos) in the process.
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| positrons | e+
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| neutrinos | neutral charge
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| CNO cycle | Happens in high mass stars.
12C + 4X1H + 2Xe- = 12C + 4 He* gamma rays + neutrinos.
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| gamma | gamma rays
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| ν | neutrinos
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| CNO produces energy for stars about _______. | 1.5 M.
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| Descriptions of high-mass stars | convection mixes hydrogen in the core, which increases the amount available for fusion. Once H is exhausted, the star leaves the M-S and expands and cools.
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| What mass classifies a high-mass star? | Mass > 8M. [O5, B0, B5 stars]
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| Super giants | upper right corner of the H-R diagram. He is ignited in a nondegenerate core which causes the central temperature to rise and heavier elements to fuse/generate energy. Will fuse elements up until iron.
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| The more massive the star, the heavier the elements that can fuse.
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| Instability strip | the temperature and luminosity results in a pulsating star
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| pulsating variable stars | ones that move across the H-R diagram.
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| Cepheid variables | high-mass supergiants. 1 to 100 day periods. more luminous stars have longer periods.
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| RR Lyrae variables | low-mass stars on the horizontal branch. less luminous than cepheid variables.
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| End of Fusion | fusion of iron or more massive elements requires energy. fusion stops and the core collapses.
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| Final days of a high-mass star | each stage of burning is progressively shorter with Silicon burning only lasting a few days.
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| Chandrasekhar limit | the limit on the mass that an electron degenerate object can have before gravity wins. 1.4 M.
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| Type II supernova |
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| nucleosynthesis | new elements are created in a nuclear explosion.
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| neutron stars | Type-II supernova leaves behind a neutron-degenerate core or neutron star.
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| pulsar | rapidly rotating neutron stars. highly magnetized with a beam of radiation sweeps by earth like a lighthouse beam.
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| black holes | if the mass of a neutron star exceed 3M. it will collapse to a black hole. Can form directly from Type II supernova or from accretion by a neutron star in a binary system.
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| star clusters | bound groups of stars.
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| main sequence turnoff | location gives cluster age. Yound clusters still have massive stars on the Main-Sequence.
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