Dates: –! Monday, Oct. 4th ! –! Tuesday, Oct. 5th ! Starts at 8pm until 10pm (expect to spend ~40 mins) –! Wednesday, Oct. 6th ! th –! Thursday, Oct. 7 ! Go to assignment page on –! Monday, Oct. 11th " class website for more info. –! Tuesday, Oct. 12th " This Class (Lecture 19): –! Wednesday, Oct. 13th You MUST download HW7 due Monday! Death of Massive Stars th worksheet before you go. No lecture on Monday– –! Thursday, Oct. 14 th Next Class: Computer lab opportunity –! Monday, Oct. 18 Can be cloudy, so check Killer Supernova –! Tuesday, Oct. 19th webpage before you go.

Music: We Are All Made of Stars–

Did you go to the Observatory yet? •! Massive stars do not live very long. •! Massive stars– making heavy elements. a)! Yes, it was okay. •! Supernova b)! Yes, it was cool! c)! Yes, it was the highlight of my life so far! d)! Yes, but it was boring. e)! No, but I will do so as soon as I can, I promise. I had other things I had to do, but I really, really want to go and I will make it a top priority in my life! " ! a.k.a. dwarf stars " ! 91% of all nearby stars

Altair Type A8 V

Vega Sun Type A0 V Type G2 V

61 Cygni A Proxima Centauri Type K5 V Type M5 V Regulus Type B3 V

" ! 10-100x the radius of the Sun " ! Up to 1000x the radius of the Sun Betelgeuse " ! Temperatures 3,000 – 20,000 K " ! Extremely rare: ~ 0.1% of local stars Type M1.5 Ia " ! Rare (< 1% of local stars)

Alnitak A Type O9 Ib Thuban Type A0 III Capella A Type G5 III

Rigel Type B8 Ia Arcturus Bellatrix Sun Sun Type K1 III Deneb Type B2 III for comparison for comparison Type A1 Ia Kinds of Dwarfs

" ! About the size of the Earth Red dwarf Just a very cool main- " ! Very hot: 5,000 – 20,000 K sequence star " ! About 8% of local stars

Sunspot Gliese 229A White dwarf White-hot burned-out core of a star SDSS J1254-0122

Sirius B Earth for comparison Sirius B

Black dwarf Sun for A very old cooled Brown dwarf comparison Not a star at all; wasn’t UKIRT/JAC white dwarf massive enough

•! Luminosity is proportional to Mass Sun is converting •! Larger range in luminosity than 700 million tons of 6 H into 695 million mass (10 vs. 100) tons of He every •! Higher mass = higher luminosity, second! higher temp, and large radius BUT, a 20 solar •! Lower mass = lower luminosity, mass star is using lower temp, and smaller radius it’s fuel 36,000 •! Only on Main Sequence! times faster! •! Star formation A massive star on the main sequence is where on the - Take a giant molecular cloud core with its associated gravity HR diagram? and wait for 104 to 107 years. •! Main sequence life (depends on mass!) a)! Upper right. - Few x 106 years to more than age of Universe - Thermonuclear burning of H to He b)! Upper left. c)! Bottom right. •! Death - Exhaust hydrogen d)! Bottom left. - Red giant / supergiant - White dwarfs, supernova neutron stars, e)! Middle. black holes

Red giant Shell hydrogen Main sequence burning Core hydrogen burning

Tcore ~ 16 million K Asymptotic branch giant Shell helium burning Helium flash

Horizontal branch Core helium burning Low-mass stars Massive stars Tcore ~ 100 million K •! High-mass stars: “gas guzzlers” •! High-mass stars do fusion –! Very bright by a different process –! Consume hydrogen fuel supply •! Called the CNO cycle very quickly –! Still converts 4 hydrogens –! Only live for millions of years on the main sequence into 1 helium –! Uses a carbon nucleus as a catalyst •! Quicker reaction •! Requires very high temperatures in the core –! More than low-mass stars (like the Sun) can produce The CNO Cycle

5 x 106 yr Red supergiant •! For stars with an initial Main sequence Shell hydrogen burning Core hydrogen burning mass of more than 10 Tcore ~ 40 million K solar masses 106 yr Helium flash •! The final state will no C Burning Core longer be a white dwarf. 105 yr •! Let’s follow more 105 yr 103 yr carefully the life path Blue supergiant Red supergiant of a high mass star– it’s Core helium burning Core carbon burning Tcore > 600 million K short sweet and ends Tcore ~ 200 million K Red supergiant with a bang! Shell helium burning

White Dwarf A1: A 150 solar mass star! •! Outer envelope of the •! Similar to lower-mass stars in star grows larger and the first few stages, just quicker. cooler •! When the hydrogen supply runs –! Up to 5 AU in size! out the core starts to contract –! Unlike a low mass •! Hydrogen shell star, brightness does burning (around the helium core) not increase dramatically starts Core collapses •! Eventually, core is hot •! The outer envelope expands enough that it can fuse quickly becoming a red helium atoms together supergiant (non-degen gas, so no flash) –! Star contracts and heats up –! Now a blue supergiant

•! Helium fusion is not the end for massive stars What causes a high-mass star to leave the main •! Cycles of core contraction, heating, ignition sequence? •! Ash of one cycle becomes fuel for the next –! hydrogen ! helium a)! Just gets tired of the main-stream media and –! helium ! carbon & oxygen –! carbon ! neon, sodium, & magnesium lifestyle. –! neon ! b)! Runs out of hydrogen in the core. oxygen & magnesium –! oxygen ! c)! Runs out of helium in the core. silicon & sulfur d)! A shell around the core begins to burn helium. –! silicon ! iron e)! A shell around the core begins to burn hydrogen. •! Onion-skin like structure develops in the core Supernova Carbon •! Has layers…. like an Ogre.. Blue supergiant ignition Helium ignition Red supergiant

Main sequence

http://servantsthoughts.blogspot.com/2007/08/onion-theory.html

•! Supergiants “burn” heavier and heavier atoms in the fusion process •! Each stage faster than the last •! After iron - no fuel left! –! It requires energy to produce heavier atoms

Stage Temperature Duration H fusion 40 million K 7 million yr He fusion 200 million K 500,000 yr C fusion 600 million K 600 yr

Ne fusion 1.2 billion K 1 yr O fusion 1.5 billion K 6 mo Si fusion 2.7 billion K 1 day

http://rainman.astro.uiuc.edu/ddr/stellar/index.html Values for a 25MSun star Supernova • Completely out of gas! Carbon ! Blue supergiant ignition Helium •! Hydrostatic equilibrium is gone. ignition Red supergiant •! The iron core of the star is supported by electron

Main sequence degeneracy pressure –! Same pressure that supports a white dwarf •! Eventually, gravity wins… –! This happens when the core is > 1.4 solar masses and no more outward pressure. –! Remember the Chandrasekhar limit

e e e e e Supernova p p p p Carbon p e e e e Blue supergiant ignition p p p p p Helium e e e e e e ignition p Red supergiant p p p p

Matter in the core of Electron-degenerate a normal star matter Main sequence 1 ton per cubic cm n n n n n n ! n n n n n n ! n n n ! n n n n n n n n n Neutrinos produced Neutron-degenerate matter as electrons are 100 million tons per cubic cm forced into nuclei What is the force that supports a white dwarf but can •! When core is greater than 1.4 M – core collapse! not support a massive stellar core. sun –! From 1,000 km across to 50 km in 1/10th of a second a)! Pressure from fusion –! Nearly 10% speed of light! b)! Pressure from CNO fusion •! The core is transformed into a sea of neutrons c)! Electron degeneracy pressure –! Electrons are squeezed into protons, d)! Gravity pressure neutrinos released –! High energy gamma rays produced e)! Neutron degeneracy pressure –! The core has nuclear density! –! It Earth has same density, it would be 1000 feet in diameter

•! Hitting the compressed core is like •! Core suddenly collapsed hitting a brick wall and the envelope •! Envelope has nothing left gas reverses direction– blow-back. to stand on –! But, by itself not enough to destroy star. •! Envelope falls at –! Material is so dense, that it is slightly significant fraction of the opaque to the neutrinos produced speed of light, slamming –! And 1058 neutrinos! into compressed core –! Neutrinos give the shock a “kick” –! Rips the outer layers of the star apart •! Star explodes in a supernova http://www.spacetelescope.org/images/screen/heic0609c.jpg

•! The energy is enormous! The visible light is around only 1% of the energy output! –! 99% of the energy in the form of neutrinos •! > 90% of the mass of star is ejected into space! –! Fast, hot,

•! The lifetime battle against gravity is lost. •! The core collapses under its own weight. •! Much of the mass of the outer region of the star, bounces back into space.

In the astroblaster demo, what did the little red ball represent?

a)! The inner core of the massive star b)! The envelope of the massive star c)! A low-mass stellar companion to the high mass star. d)! Iron. •! The star goes supernova and explodes. Some of C, O, P, S, Si, and Fe get carried away. At this point, even heavier elements can be made during energy consuming fusion reactions •! These by-products are blasted into space (>90% of star)

•! Supernovae provide much of C. Lithgow-Bertelloni (UM) the building blocks for planets… and us! •! We are recycled supernova debris! •! We are Star stuff.

http://www.youtube.com/watch?v=ptwEV0xhTzI&feature=related Delenn, B5 http://www.youtube.com/watch?v=8MHb6_35XJM 2:00 - 3:06

http://www.youtube.com/watch?v=2afotzgrFbE