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Slide 2 Slide 3 On the Main Sequence What holds a star up while it is on the MS? Parts of a MS star How does energy get out? Radiation & Convection May take a million years to reach the surface. Slide 4 Brown Dwarfs : Stars with core mass 1.4 and 1.4 and 1.4 and 1.4 and600 MillionK Carbon in the Core ignites. C fuses to form : Ne, and O Core at the end of Carbon Burning Phase:"> C-O Core collapses until: T core > 600 MillionK Carbon in the Core ignites. C fuses to form : Ne, and O Core at the end of Carbon Burning Phase: Slide 40 1. Hydrogen burning: 10 Myr 2. Helium burning: 1 Myr 3. Carbon burning: 1000 years 4. Neon burning: ~10 years 5. Oxygen burning: ~1 year 6. Silicon burning: ~1 day Finally builds up an inert Iron core Nuclear burning continues past Helium Things happen fast! End of the line!! Slide 41 Massive star at the end of Silicon Burning: Onion Skin of nested nuclear burning shells Slide 42 Protons & electrons form neutrons & neutrinos. Collapse is final. At the start of Iron Core collapse: Radius ~ 6000 km (~R earth ) Density ~ 10 8 g/cc A second later!!, the properties are: Radius ~50 km Density ~10 14 g/cc Collapse Speed ~0.25 c ! Slide 43 Supernova explosion Neutron degeneracy pressure halts the collapse Material falling inwards rebounds. Outer layers of the atmosphere, including shells, are blown off in a violent explosion called a supernova. The star will outshine all the other stars in the galaxy combined. Slide 44 The ejected material often attain speeds of 100,000 km/sec. Elements heavier than Lead are produced in the explosion and ejected into space. Stars do recycle. Close to 150 supernova remnants have been detected in the Milky Way. There are smaller numbers of massive stars and so smaller amount of explosions. Slide 45 The Famous Supernova Before At maximum type II Supernova SN 1987A Slide 46 Supernova remnants Cas A in x-rays (Chandra) Vela SN1998bu Remnant of SN386, with central pulsar (Chandra) Cygnus Loop (HST): green=H, red=S +, blue=O ++ Slide 47 The rings of SN 1987A are from previous mass loss Slide 48 1a is binary with a White Dwarf Type II : Hydrogen lines in the spectrum Slide 49 Supernova explosion 1, The iron core collapses 2. Neutrons stop the collapse 3. The rebound of the core sends shock waves causing an explosion that blows the outer atmosphere into space as a super nova Slide 50 The Crab Nebula. A supernova that, according to the Chinese, exploded in 1054. Despite a distance of ~ 7,000 light-years, the supernova was brighter than Venus for weeks before fading from view after nearly two years. Even today, the nebula is still expanding at more than 3 million miles per hour. Slide 51 Structure of a Neutron Star Diameter~ 12 km in diameter Mass -about 1.4 times that of our Sun. One teaspoonful of material would weigh a billion tons! Rotation Rate: 1 to 100 rotations/sec Slide 52 The magnetic axis is miss-aligned with the rotation axis of the neutron star. The star's rotation sweeps the beams outward as it rotates. If we are in the sight path, will see regular, sharp pulses of light (optical, radio, X-ray.) Lighthouse Model: field generates a Spinning magnetic a strong electric field. Slide 53 Slide 54 Pulsars: emitted sharp, 1 millisecond-long pulses every second at an extremely repeatable rate. A typical pulsar signal, received with a radio telescope Slide 55 The connection between pulsars and neutron stars was the discovery of a pulsar in the crab nebula. Slide 56 Iron Slide 57 Proto-stars (born in cool gas GMC) Main Sequence Stars (H Fusion) Core Mass (CM) > 1.4 MO Red Super Giant Yellow Super Giant Supernova (Type II) Neutron Star Black Hole CM > 1.4 & < 3 CM > 3 Black Dwarf Red Giant Red Super Giant Planetary Nebula White Dwarf Binary can produce Type ia supernova Brown Dwarf CM Black Holes We know of no mechanism to halt the collapse of a compact object with mass > 3 M sun. It will collapse into a single point a singularity: => Becoming a Black Hole! Slide 60 Honeycutt H Has He Caused C No Ne Oxford O Student Si Injury (Iron) Fe To memorize this sequence, use this : Massive stars form the following:H, He, C, Ne, O, Si, Fe. Iron will not fuse. Low mass stars form only H, He, C, O Slide 61 Thanks to the following for allowing me to use information from their web site : Nick Stobel Bill Keel Richard Pogge NASA