Star%20Deaths

1
Star Deaths

• Mass matters!

2
Star Deaths

• Stars die when fusion reactions stop (still
  contains heat energy)
• Mass at the time of death determines the form of
  the corpse
• Stars lose mass before their corpse forms (winds,
  explosions)
• Corpses last forever

3
Star Deaths

• Mass (at death)
• gt 0.08 solar mass
• 0.08 to 1.4 solar masses
• 1.4 to 3 solar masses
• gt 3 solar masses

• Corpse
• Brown dwarf
• White dwarf
• Neutron star
• Black hole!

4
White Dwarf

• Mass bit less than the suns
• Size about that of the earth
• Density about 109 kg/m3
• Made of electron gas (degenerate-greater mass,
  smaller size)
• Shines by outflow of stored heat

5
Neutron Star

• Mass around 2 solar masses
• Size about 10 km (city!)
• Density about 1017 kg/m3 (atoms nucleus!)
• Made of neutron gas (degenerate)
• Made in supernova explosions

6
Black Holes

• Mass ANY expect 3 to 10 solar masses from
  normal star death
• Size Schwarzschild radius-a few km(about 3 km
  for sun directly proportional to mass)
• Escape speed equal to or greater than speed of
  light
• Inside mass has zero volume, infinite
  densitythe singularity

7
Black Holes

• Made of warped spacetime (essentially
  permanent!)
• Time is frozen at the Schwarzschild radius (to
  outside observer) never sees objects fall in
• As black holes gain mass, they grow in size (can
  never shrink)

8
Black Holes

• Measure mass by visible orbiting body (Newtons
  version of Keplers 3rd)
• Most likely found in binary stars(black hole
  regular massive star)
• Are not cosmic vacuum cleaners (but dont get up
  close!)

9
Black Holes X-rays

• Matter from companion star falls into an small
  accretion disk (about 10 km) around the black
  hole
• Disk heats up to about 10,000,000 K (conversion
  of gravitational energy)
• Opaque material of disk emits x-rays (blackbody)
• Search in binary x-ray sources

10
Supernovas!

• Peak at 10 billion solar luminosities
• Lifetime about a few months
• Total energy about 1046 joules (99 as
  neutrinos)
• Blows off a few solar masses of material at
  thousands km/s (supernova remnant)

11
Supernovas!

• One type Old massive star (about 10 solar
  masses) with unstable iron core
• Core collapses in about 1 second!
• Implosion releases gravitational energy, high
  temps for fusion reactions
• Fuses elements heavier than iron blasted into
  space

12
Neutron Stars Pulsars!

• Supernova core collapse makes neutron star
  (usually!)
• Pulsars usually found near center of supernova
  remnants
• Pulsars emit very short pulses (ms) at very
  regular intervals
• Rapidly-rotating, highly-magnetic neutron stars
  are pulsars