1101_23_supernovae

Announcements: Assessment today 1:35pm à 1:35pm tomorrow. 1 Evolution of Low-Mass stars M < 4 M sun No C Burning! 40,000 20,000 10,000 5,000 2,500 10 6 10 4 10 2 1 10 -2 10 -4 Temperature (K) Luminosity (L sun ) Main Sequence C-O Core C-O White Dwarf (forever) Envelope Ejection 0.1Myr Red Giant Branch 1Gyr He core contraction, H burning shell Horizontal Branch 100 Myr He core burning Asymptotic Giant Branch C-O core contraction, H, He shell burning 10 Gyr t ms ~1/M 3 H core burning Helium Flash 2 40,000 20,000 10,000 5,000 2,500 10 6 10 4 10 2 1 10 -2 10 -4 Temperature (K) Luminosity (L sun ) Main Sequence Red Supergiant Blue Supergiant t ms ~1/M 3 H core burning CNO cycle. He core contraction, H burning shell He core burning H burning shell Red Supergiant C-O core contraction, H, He shell burning Then, C, burning to ONeMg WD He Flash . Intermediate-Mass stars 4 < M < ~8 M sun ONeMg White Dwarf (forever) 3 40,000 20,000 10,000 5,000 2,500 10 6 10 4 10 2 1 10 -2 10 -4 Temperature (K) Luminosity (L sun ) Main Sequence Red Supergiant Blue Supergiant Fe core collapse BOOM! t ms ~1/M 3 H core burning CNO cycle. He core contraction, H burning shell He core burning H burning shell C-O core contraction, H, He shell burning Then, C, Ne, O, Si burning He Flash . High-Mass stars M > ~8 M sun 4

Massive Star Supernovae Astronomy 1101 5 Key Ideas: End of the Life of a Massive Star. Iron core collapse & core “ bounce ” Neutron star formation. Supernova Explosion: à How? We don’t really know. à Then, envelope ejection, supernova remnant Neutron stars and pulsars. 6 Last Days of a Massive Star Burns a succession of nuclear fuels: • Hydrogen burning : 10 Myr • Helium burning : 1 Myr • Carbon burning : 1000 years • Neon burning : ~10 years • Oxygen burning : ~1 year • Silicon burning : ~1 day Builds up an inert Iron core in the center, supported by electron degeneracy pressure (like a WD) 7 End of Silicon Burning Phase: Inert Fe-Ni Core Si Burning Shell O Burning Shell Ne Burning Shell C Burning Shell He Burning Shell H Burning Shell Envelope: ~ 5 AU Core Radius: ~1 R earth 8

300 km Burrows et al. (1995) Collapse can lead to explosion in ~1 sec! ࠵? ! + ࠵? → ࠵? + ࠵? " Electrons combine with protons to make a neutron star: Escaping neutrinos interact with infalling matter, heating it: ࠵? " + ࠵? → ࠵? ! + ࠵? Collapse to nuclear density. “Bounce” off the strong force (like billiard balls). Shockwave is energized and explodes surrounding star 13 Sean Couch (Michigan State) 27M sun star 15 Vartanyan et al. 2018 16 Vartanyan et al. 2018 Melson et al. 2015 17

Supernova Shocks its Host Star Kifonidis et al 19 CTIO We know collapse leads to explosion, sometimes. Maybe most of the time. But, sometimes black holes. 20 Before Feb 23, 1987 On Feb 23, 1987! Australian Astronomical Observatory - Malin 21 Supernova 1987a Nearest visible supernova since 1600’s. February 23, 1987: • 15 M sun Supergiant Star SK–69 o 202 Exploded in the Large Magellanic Cloud. • Saw a pulse of neutrinos, then the explosion. Amount of energy radiated matches models. • Confirmed the basic picture of collapse. • Continued to follow it for the last 25 years. • Still no visible neutron star… 22

Betelgeuse It’s supernova might be nearly as bright as the full moon. For weeks. D ~ 200 pc (600 lyr) L ~ 100,000 L sun R ~ 1000 R sun T ~ 3500 K M ~ 20 M sun NASA/ESA/HST 27 Other Supernova Remnants (x-rays) Chandra 28 Neutron Stars are the collapsed cores left after core- collapse supernovae of massive stars. 8 < M initial < 15 or 25 or 30 M sun (?) Held up against gravity by Degenerate Neutron Pressure. Shine only by residual heat : no fusion or contraction Mass: ~1.2 – 2.1 M sun Radius: ~12 km Density: ~2x10 14 g/cc! Escape Speed: ~0.7c! Rotation periods: 0.002 – 10 s! Magnetic fields: 10 10 – 10 15 G! Properties: 29 Neutron stars were accidentally discovered in 1967. Jocelyn Bell (a Cambridge grad student) and Anthony Hewish (her PhD adviser) discovered pulsating radio sources while looking for something else. Pulsars = Pulsating Radio Sources 30

Radiation Beam Magnetic Field Spin Axis Pulsars are rapidly spinning, magnetized neutron stars. Lighthouse Model of Pulsars: Strong magnetic field and rotation create beams of intense radiation. Pulsar slow its rotation as it ages. It “spins down.” Spinning magnet sheds energy. They emit sharp millisecond-long pulses every spin period from radio to X-rays. Hundreds of pulsars known, spin periods of 2 ms to > 10 s. 31 Lighthouse model for pulsars Video by Michael Kramer (MPIfR/JBCA) 32 The race to explosion or black hole … The “proto”-neutron star is supported by: Normal gas pressure (P ~ density x temp) Neutron degeneracy pressure (P is temp independent) Neutron star mass is growing because of infalling matter. On a timescale of just ~ 1 second the core goes from about 1.4 M Sun à larger than 2.5 M Sun . Neutrinos cool the core. Less thermal pressure (KH contraction) If M > 2.5 M sun (or so), neutron degeneracy pressure fails and then à BH formation… 33