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Supernova Explosions 1 billion times brighter then the Sun for a few months PHYS 162 1 Supernovas • 10-20 supernovas occur every1000 years in a galaxy the size of the Milky Way (~200 billion stars) with ~15% being type Ia • 8 observed in last 2000 years (185, 386, 393, 1006, 1054, 1181, 1572, 1604) • Hard to observe if on “opposite” side of Milky Way all recent observed SN are in other galaxies PHYS 162 2 1572 (Tycho Brahe) and 1604 (Kepler) In Milky Way both probably Type Ia PHYS 162 3 Supernova 2014j – Jan 2014 In M82 (Ursa Major). Type Ia. Closest of this type observed in modern times. 11.5 million LY away. Discovered at undergrad session Univ Coll London (SN1972 e was 11 MLY but pre “modern”) PHYS 162 4 Supernova PTF 11kly – Sept 2011 In Pinwheel Galaxy. Type Ia. 2nd closest Ia observed in modern times. 21 million LY away PHYS 162 5 Supernova 1987a (in movie) Large Magellanic Cloud Type II 180,000 LY away PHYS 162 6 Supernovas and Core Collapse • massive stars have fusion to heavier nuclei (Neon, Silicon, Sulpher, etc) • end up with core of Iron nuclei plus 26 unbound “free” electrons for every Fe • electrons are “degenerate” as so close together. This causes them to provide most of the pressure resisting gravity • enormous stress. If electrons “give way” leaves “hole” in center of star PHYS 162 7 Supergiant Iron Core PHYS 162 8 During Supernova core collapse gives 200 billion degrees energetic photons • breaks up many nuclei Fe 26p + 31n O 8p + 8n • new nuclei form photons, n, and p strike shell around core • p + e n + neutrino 1. Burst of neutrinos. 1000 times more energy than from light (photons) 2. Leftover neutron star • PHYS 162 9 Core Collapse core collapses into mostly neutrons – very hot outer layers rush into “hole” smashing into shock wave from core happens when mass of core > 1.4 Mass Sun. Chandrashekar limit PHYS 162 10 Detection of neutrinos from SN1987A in Japan and Ohio SN produced 1058 neutrinos 1015 n/cm2 at Earth 1018 neutrinos from SN passed through any person’s body Traveled 175,000 light years to Earth Passed through Earth 17 were detected in detectors made from 100 tons of water located in underground mines in Ohio and Japan PHYS 162 11 Nuclear Synthesis • All elements heavier than Helium are made inside stars up to Iron - fusion in Red Giants heavier than Iron (and some lighter) - Supernova explosions • Stars lose matter at end of life-cycle becoming Red Giants (can detect) Supernova debris (can detect) and this matter forms new stars (and planets and us) PHYS 162 12 Nuclear Synthesis during Supernova • mostly neutrons attaching themselves to nuclei say Fe(26p + 31n) U(92p + 146n) • new nuclei form that have 10-20-50 “too many” neutrons • they Beta decay n p very rapidly now having nuclei with more protons than Iron • Cycle repeats itself – happens very fast “rapid” PHYS 162 13 Cosmic Abundance of Elements H = 92% of elements = mass-fraction 74% He = 8% = mass-fraction 25% All others < 1% mass-fraction about 1% Discovered by Cecilia Payne about 1921, but she didn’t become Harvard faculty until 1856 as “no female faculty” PHYS 162 14 Supernova Debris SN1987a PHYS 162 15 Supernova Debris Crab Nebula M1 Cassiopeia A maybe Supernova 1054 (observed by observed in 1680 Chinese and Arabs). Has neutron PHYS 162 star 16 NEUTRON STARS In supernova explosion core collapses • e- + p n + n • neutrons remain giving neutron “star” about 1% protons/electrons • very hot (200 billion degrees) and very small (10-30 km - DeKalb County) • so very, very dense. 1 cm3 100 million tons PHS 162 17 White Dwarf Neutron Star Mass (relative to Sun) Radius 1.0 (always < 1.4) 5000 km 1.5 (always < 3) 10 km Density 106 g/cm3 1014 g/cm3 Properties determined by “degenerate” electrons and neutrons. neutron/electron mass ratio = 2000, neutron star much smaller and denser Senior level physics classes do the quantum mechanics which predict radius versus mass PHS 162 18 HR Diagram Worksheet • For Sirius B use spectral class B1 • Vertical axis is Luminosity and a log scale so do .00001, .0001, .001, .01, .1, 1, 10, 100, 1000, 10,000, 100,000, 1,000,000 with 2 lines separating each • After labeling horizontal axes with spectral class B0M10, add on below them the surface temperature with: B0= 24,000 A0=11,000 F0=7000 G0=6000 K0=5000 M0=4000 PHYS 162 19 HertzprungRussell Diagram Plot Luminosity versus surface temperature PHYS 162 20