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Supernova and Neutron Stars For heavy white dwarves with a companion star • acquire mass, if becomes > 1.4 M(Sun) SUPERNOVA (Ia). p + e n + neutrino • Usually leaves neutron star For high mass stars • fusion continues beyond C,O to Iron • if Mass(core) > 1.4 M(Sun) core collapses in SUPERNOVA (II) • leaves either Neutron Star or Black Hole • Most SN are this type PHYS 162 1 White Dwarves Mass vs Radius S. Chandrashekar 1910-1995 worked out in 1930 on boat from India to England prior to grad school. Later became professor at Chicago. Nobel prize 1983 Earth radius PHYS 162 2 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 provide most of the pressure resisting gravity • enormous stress. electrons “give way” leaves “hole” size of Earth in center of star PHYS 162 3 Supergiant Iron Core PHYS 162 4 During Supernova core collapse gives 200 billion degrees very high energy photons • breaks up many nuclei Fe 26p + 31n O 8p + 8n • new nuclei form photons, n, and p strike shell around core see in SN debris • p + e n + neutrino (and nuclei decaying) 1. Burst of neutrinos. 1000 times more energy than from light (photons) 2. Leftover neutron star • PHYS 162 5 Core Collapse core collapses into mostly neutrons – very hot outer layers rush into “hole” smashing into shock wave from core Many nuclear reactions form heavy elements Core=30 km wide Hole=13000 km wide Type II expends energy increasing size PHYS 162 6 Supernova Explosions 1 billion times brighter then the Sun for a few months PHYS 162 7 Supernova 1987a (in movie) Large Magellanic Cloud Type II 180,000 LY away PHYS 162 8 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 24 were detected in detectors made from 100 tons of water located in underground mines in Ohio, Russia and Japan PHYS 162 9 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 10 Supernova Debris SN1987a PHYS 162 11 Supernova Debris Crab Nebula M1 Cassiopeia A maybe Supernova 1054 (observed by observed in 1680 Chinese and Arabs). Has neutron PHYS 162 star 12 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 13 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 14 Angular Momentum + Neutron Stars Angular momentum = MASS x VELOCITY x RADIUS decreasing RADIUS increases VELOCITY Angular momentum is conserved: spinning chair ice skater formation of neutron star in collapse of larger spinning star NEUTRON STARS II • spin rapidly from >100 Hz to less than 1 Hz • EM radiation from protons/electrons + spin large magnetic fields • observe as repeating flashes of light PULSARS and seen in debris of known supernova explosions • discovered in 1967 by grad student Jocelyn Bell. Her advisor Anthony Hewitt won Nobel prize. Found in Crab Nebula where Chinese had recorded a supernova in 1054. First called LGM for “little green men” PHS 162 16 Crab Nebula radio infrared visible period = 30 Hz or 0.033 sec and can be “seen” in visible and X-ray X-ray PHS 162 17 Rotating Neutron Star PHS 162 18