Complications in Binary Systems
Can move mass between stars
• 1st (massive) star becomes red giant
• Its envelope transferred to other star
• Hot (white dwarf) core exposed
• 2nd star becomes red giant
• Its envelope transferred to white dwarf
– Accretion disk around white dwarf
• Angular momentum doesn’t let material fall
directly to white dwarf surface
– Recurrent nova explosions
• White dwarf hot enough for fusion, but no
Hydrogen fuel
• New fuel comes in from companion
• Occasionally ignites explosively,
 blowing away remaining fuel