Chapter 21 - Physics1902 Novae,Supernovaeand Bursters...

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1 Physics 1902 Novae, Supernovae and  Bursters Lecture W9.a Chapter 22
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Common nuclei: commonest isotope 2 Name Symbol Z (Charge) A (#neutrons+proto ns) Hydrogen H 1 1 Deuterium D 1 2 Helium He 2 4 Carbon C 6 12 Nitrogen N 7 14 Oxygen O 8 16 Sodium Na 11 23 Magnesium Mg 12 24 Silicon Si 14 28 Calcium Ca 20 44 Iron Fe 26 56 Cobalt Co 27 59 Nickel Ni 28 58
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3 What happens to more massive stars Helium reaches ignition temperature early and before degeneracy conditions set in Helium burning is not so explosive Above 8 solar masses temperatures allow carbon fusion to occur Life after the main sequence is short for massive stars Death is normally a supernova
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4
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5 Novae and Supernovae Occasionally stars are seen to increase in brightness by a huge factor over a short time In many cases, the original star was not observed so these were ‘new stars’ or novae
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6 March 1935 May 1935 Nova in Hercules
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7 Luminosity increased by 60,000 Nova Light curve
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8 Nova seen in Nebulae Novae were observed in nebulae – in particular in spiral nebulae When it was realized that these ‘galaxies’ were extremely distant it was obvious that these had to be ‘Super Novae’
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9 Types of Novae We will look at 3 main types of Novae Classical Novae Type I Super Novae Type II Super Novae We will take them in the opposite order
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10 Type II Supernovae A type II supernova occurs at the end of the life of a massive star We pick up the star with a burning carbon core
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11 Nuclear Physics Aside
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12 Energy win from Nuclear Fusion We can gain energy by fusing nuclei up to iron After that energy is lost in fusion So when our core reaches iron, burning ends
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14 The final crunch The iron cannot produce energy to increase the pressure to resist the pull of gravity The amount of iron continues to grow as burning of lighter elements proceeds Central temperature reaches 10 10 K At this temperature the core produces black body radiation in the MeV range or hard gamma rays
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15 The collapse Gamma rays break up nuclei by photodisintegration This robs the core of energy cooling it and reducing the pressure Core is now almost pure electrons, protons and neutrons We get reactions like P + e - -> n + ν This robs the core of degeneracy pressure and cools it as the neutrinos fly off
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This note was uploaded on 10/05/2010 for the course PHYS 1902 taught by Professor Staff during the Winter '10 term at Carleton CA.

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Chapter 21 - Physics1902 Novae,Supernovaeand Bursters...

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