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Stars, Test 2

Test 2 for Stars the Galaxy and the Universe

The Main Sequence EVERYTHING this test is about. Most stars are on the Main Sequence.dd
The more massive a star, the more... luminous, larger, and hotter.
What determines the location of a star along the main sequence? The Mass
Interstellar medium What stars are made out of. Gas and dust between the stars. Most is gas; 1% is interstellar dust.
No stars less than about _____ have ever evolved off the main sequence. 0.8M.
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.
Fun facts about the dust portions solid grains, or "interstellar soot" (iron, silicon, carbon, and more). blocks visible light.
Size of interstellar dust large molecules about 300nm
Interstellar reddening Dust blocks short wavelengths more efficiently. Whilst long wavelengths such as infrared and radio waves penetrate dust.
Temperature of dust typically cool (10-300K). Will emit infrared radiation.
Gas temperatures ~10^6 K (very hot). Heated by shock waves from supernovae.
H II regions T~10^4 K. Hydrogen heated and ionized by ultraviolet light from hot, luminous stars
Ionized stripped of one or more electrons
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.
Interstellar clouds Includes most interstellar gas. Cool temperatures.
Intercloud gas regions of hot gas which lies between interstellar clouds.
Molecular clouds interstellar clouds which is cold enough for hydrogen to be in the H2 molecule. 120 light-years in size. Where stars form.
Temperature of Molecular clouds 10K
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.
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.
cores. Caused by collapsing molecular clouds.
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.
protostar center of the star that is surrounded by large envelope of infalling gas and dust. Large, cool and luminous. emits infrared light.
Protostellar system central protostar + disk + infalling envelope
Accreation Disk Formed from the rotating cloud material.
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.
Becoming a star When the core becomes small enough and the temperature hot enough, hydrogen fusion begins and it becomes a main sequence star.
Temperature required for fusion 10 million kelvin.
Mass required for hydrogen fusion 0.08M. (Brown dwarfs)
Evolutionary track Path of temperature and luminosity with time. Protostars of differeny masses follow different paths on their way to the main sequence.
Hayashi track
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
Herbig-Haro objects when powerful jets collide with interstellar medium
Star clusters Gravitationally bound groups of stars
Time takes to form stars May take millions of years. High-mass stars take less time to form and quickly evolve.
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.
positrons e+
neutrinos neutral charge
CNO cycle Happens in high mass stars. 12C + 4X1H + 2Xe- = 12C + 4 He* gamma rays + neutrinos.
gamma gamma rays
ν neutrinos
CNO produces energy for stars about _______. 1.5 M.
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.
What mass classifies a high-mass star? Mass > 8M. [O5, B0, B5 stars]
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.
The more massive the star, the heavier the elements that can fuse.
Instability strip the temperature and luminosity results in a pulsating star
pulsating variable stars ones that move across the H-R diagram.
Cepheid variables high-mass supergiants. 1 to 100 day periods. more luminous stars have longer periods.
RR Lyrae variables low-mass stars on the horizontal branch. less luminous than cepheid variables.
End of Fusion fusion of iron or more massive elements requires energy. fusion stops and the core collapses.
Final days of a high-mass star each stage of burning is progressively shorter with Silicon burning only lasting a few days.
Chandrasekhar limit the limit on the mass that an electron degenerate object can have before gravity wins. 1.4 M.
Type II supernova
nucleosynthesis new elements are created in a nuclear explosion.
neutron stars Type-II supernova leaves behind a neutron-degenerate core or neutron star.
pulsar rapidly rotating neutron stars. highly magnetized with a beam of radiation sweeps by earth like a lighthouse beam.
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.
star clusters bound groups of stars.
main sequence turnoff location gives cluster age. Yound clusters still have massive stars on the Main-Sequence.
Created by: 29pachyderm