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32 Cards in this Set
- Front
- Back
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dark nebula
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dense cloud of gas and dust where dust absorbs visible light and obscures starts behind it
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cloud collapse can be triggered by:
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-nearby supernova
-cloud passing through spiral arm of galaxy -cloud collision |
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protostar
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surrounded by dense gas and dust clouds from which they form
-best observed in infrared because IR is less absorbed by dust than visible light is |
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H fusion begins in core when...
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central temp of protostars reaches 10^7K
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Evolutionary track
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path of star in H-R diagram as L and T change
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track of protostar approaches main sequence when...
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starts have high luminosity and low temperature
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reflection nebulae
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bluish haze seen around hot, young stars
- due to interstellar dust which reflects blue light more effectively than red light -blue haze is reflected star light -stars behind dust appear redder |
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main sequence limits
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lower- below .8 M central temp is too low for fusion
upper- above about 100 M radiation pressure blows starts apart |
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brown dwarf
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failed star
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evolution of 1M Star
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main sequence, red giant, helium flash, horizontal branch, second red giant, planetary nebula, white dwarf
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main sequence evolution
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nuclear fusion in core converts H to He
Star leaves main sequence when H is used up in core -Sun spends 10^10 years on main sequence (more massive stars burn through H faster) |
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Red Giant phase
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H fusion ends in core but continues in shell around core
Gravity causes core to contract and heat Energy output from shell increases- outer region of star expands and cools- expansion is caused by increased pressure star is now a red giant |
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red giant properties
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big, bright, cool
R= 100 R of sun L= 1000 L of sun T= 3500 K |
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helium flash
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when central temp= 10^8K, He fusion begins in core
Triple a process: 3He --> C + energy |
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horizontal branch
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He fuses to C in core
Core expands and cools envelope contracts and becomes bluer luminosity is higher than sun |
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second red giant phase
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no He left in core
core is now carbon no nuclear fusion occurs in core core contracts: envelope expands star becomes red supergiant |
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planetary nebula phase
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red supergiant envelope pulsates unstably
envelope is ejected core is exposed |
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structure of planetary nebula
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expanding spherical gas shell around small, hot star
appears as bright ring in sky - can be nonspherical due to star orbiting a binary companion or disk around star produces hour glass shape |
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white dwarf phase
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hot dense core becomes white dwarf= collapsed star about size of earth
NO nuclear burning (fusion) |
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structure of white dwarf
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density: 10^9 kg/m^8= 10^6 x density of water
electrons are packed as closely as possible does NOT contract further T and L decrease in time |
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chandra limit
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maximum possible mass for a white dwarf is 1.4 M
gravity overcome electron pressure at higher masses a more massive burned out star must collapse to smaller size and higher density work won 1983 nobel |
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open star cluster
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found in disk of galaxy
example: pleiades stars are young, recently formed most starts are near main sequence most massive stars are just leaving main sequence age= 2 x 10^7 years |
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globular star cluster
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found in bulge/halo of galaxy
contain only old stars, ages > 10^10 year almost no stars are present on upper main sequence b/c have moved on to next phases |
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main sequence turnoff
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location in H-R diagram of stars just becoming red giants
the younger the cluster the higher the mass of the turnoff stars the location of the turnoff determines the age of the cluster |
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evolution of high mass stars
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nuclear fusion produces elements up to iron
growing iron core does NOT undergo fusion core is only size of earth when core mass exceeds 1.4M it becomes unstable |
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supernova death of a massive star
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gravity overcomes outward electron pressure in iron core causing rapid collapse
electrons and protons combine to form neutrons neutrinos are produced pulse of neutrinos is emitted neutron pressure stops collapse when core is 20 km across pressure balances gravity again in core |
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supernova blast
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energy released by core collapse causes shock wave to travel out
rest of star explodes outward elements heavier than iron are produced in blast |
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key points of supernova
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elements heavier than H and He are produced in massive stars
supernova explosions return those elements to interstellar gas stars, planets, and life form from gas ejected by supernova |
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supernova 1987A
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-closest supernova observed in past 400 years
-observed in Large Magellanic Cloud in February 1987, distance= 160000 ly Observations:blue supergiant exploded, L increased by a few 100x, neutrino pulse seen in 2 underground detectors confirmed stellar core collapse |
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neutron stars
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ultra collapsed stellar core, produced by SN
Mass > 1.4M radius= 10km (6 miles) Size of bloomington made of tightly packed neutrons young neutron stars are found in SN remnants (Crab Nebula) |
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observation of neutron stars
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pulsing source of radio, visible, or xrays
discovered in 1967 by Jocelyn Bell using radio telescope pulse periods: .0014sec up to 700 flashes/sec first explanation: alien signals |
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pulsar model
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magnetized, rapidly rotating neutron star
magnetic and rotation axes not aligned radiation beamed along magnetic axis see flash when beams sweeps past us "lighthouse effect" |
