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MSU AST 207 - Study Guide

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129 Oct1. A fossil is a remnant or trace of the past. What is a fossil from the Big Bang?Fossil from Burgess ShaleHelium Production in BB—29 Oct• A fossil is a remnant or trace of the past. What is a fossil from the Big Bang?– There are 7 protons for every neutron– The surface of the sun is 25% He and 75% H.• What does that fossil tell about the BB?Fossil from Burgess ShaleFossil from Big BangpHepppppppppppNeutrons/protons when deuterium forms (review)• 0.001s– Temperature = 400 BK– E=40 MeV is much greater than cost to be a neutron– n:p = 1:1 •3 min– Temperature = 1 BK– E=0.1MeV is much less than cost to be a neutron–n:p= 1:7• As universe cools, #n/#pdrops.• Neutrons in deuterium are safe; they no longer change into protons. • #n/#p is a fossil from the universe at 3 min.• Deuterium forms from n & p–p + n ↔ deuterium + energy–E=0.1MeV– Deuterium is fragile• If temperature is too hot (E>0.1MeV), deuterium gets broken apart.• When temperature is cool, deuterium is stable.•2H combines to form 4He (through several reactions)How 4He is made1. When U was 10s old, what were the two most abundant constituents?A. H & 4HeB. H & nC. H & D (2H)2. Same for 10,000s (3hr).3. When U was 10,000s old, how much D (2H) was there for every ton (1000kg) of matter?A. 1 kgB. 100 gC. 10 gD. 1 g• Need to understand why elements changed during the first 3 minutes. • Model of how amount of element changes with time.10s100s 1000s2How 4He is made• What changed during the first hour?– At 1 s, neutrons & protons; minute amount of 2H (D).– Ratio n/p dropping slowly–2H, as well as 3H and 3He increases staring at 30s.–4He increases– At 200 s, 2H, 3H, and 3He drops. 4He stays high.– At 10,000s (3hr), U is primarily 1H & 4He with trace amounts of others.• Need answers– Why does n/p drop even before 10s? Very few neutrons are being incorporated in 2H.– What is beginning to happen at 30s? Why does it start then?10s100s 1000sTime →← Temp“Collecting the Fossil”•4He, 7Li, 2H, & 3He are made in BB.– Lots of 4He– Trace amounts of 7Li, 2H, & 3He. Diagnostics.• Measure abundances with spectra of “primordial objects”– First stars in our galaxy, made before much of the material had been processed through stars.– Dwarf galaxies, where material is processed through stars very slowly.• Deuterium 2H has same spectra as hydrogen 1H but slightly shifted.– Abundance of 2H: Strength of 2H spectral line compared with 1H line.O’Meara, et al., 2001, ApJ 552, 718.400km/s=d wavelegnth = wl/750Results• Horizontal bars are measurements.• Lines are models for differing amounts of photons/(n+p)• The temperature of the radiation from the BB tells us the number of photons.2. How many 1H nuclei are there for every 2H nucleus according to the measurements?3. The model for photons/(n+p) = 1011is inconsistent with the measurements. The measured 4He is too ___.A. HighB. Low• Measurements are consistent with models for photons/(n+p) = 4×1010.– 7Li is slightly off– Understanding of BB (and nuclear physics and astrophysics of stars and galaxies) is confirmed.– Surprise: Most of neutrons and protons are notin stars. Lots in gas between galaxies. Location of about 50% is not known.photons/(n+p)10910101011Ned Wright’s Cosmology


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MSU AST 207 - Study Guide

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