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Lecture 26

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PHYS 183
Tracy Webb

Lecture 26: March 18 , 2013  midterm is non-cumulative covering everything from after the first midterm & up until last Friday’s lecture  final exam will be cumulative  next Monday’s lecture is cancelled  assignment number 3 will be due April 3d  the bizarre stellar graveyard is stellar remnants  white dwarfs & binary systems, neutron stars, black holes  recall: white dwarfs o remnant of low-mass stars o supported by electron degeneracy pressure o upper limit for mass of 1.4 solar masses o gravity wins which collapses the star, but clearly pressure wins again or else it would continue to collapse o as you make them more massive, they get smaller  rearrange matter within them to support the extra mass, which makes them smaller  white dwarfs in binary systems o take low mass star & you let it evolve (burns H & He) & then it loses all outer atmospheres in a planetary nebula  then falls & cools passively essentially forever (only happens if the white dwarf is on its own) o an isolated white dwarf will simply cool & fade forever o 50% of stars are born in binary systems o but a white dwarf in orbit with a companion star suffers a very different fate o important since white dwarfs are extremely small  difficult to study them unless they are in a companion system  binary system stars o mass transfers between close stars o happens often between 2 companion stars o mass from high mass star (red giant) is stolen from the lower mass star which then becomes more massive o what happens as they evolve?  the evolution of the high mass star slows down  the evolution of the low mass star speeds up  will now go through moe massive stellar evolution  WD Novae (distinct from Supernovae) o hydrogen builds up on the surface of the star o the temperature & pressure increases as more mass is accreted o eventually the whole thing will explode o hydrogen ignites rapidly & there is a brief (week-long) burst of fusion o distinct from supernovae since just have the surface of the star exploding
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