Supernova and Neutron Stars

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

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

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

Supergiant  Iron Core PHYS 162

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

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

Supernova Explosions 1 billion times brighter then the Sun for a few months PHYS 162

Supernova 1987a (in movie) Large Magellanic Cloud Type II 180,000 LY away PHYS 162

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

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

Supernova Debris SN1987a PHYS 162

Supernova Debris Crab Nebula M1 Supernova 1054 (observed by Chinese and Arabs). Has neutron star Cassiopeia A maybe observed in 1680 PHYS 162

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

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

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

Crab Nebula radio infrared period = 30 Hz or 0.033 sec and can be “seen” in visible and X-ray visible X-ray PHS 162

Rotating Neutron Star PHS 162

Supernova and Neutron Stars