Transcript Star Deaths PowerPoint Slides

Star Deaths
Mass matters!
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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”
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Star Deaths
Mass (at death)
• > 0.08 solar
mass
• 0.08 to 1.4 solar
masses
• 1.4 to 3 solar
masses
• > 3 solar masses
Corpse
• Brown dwarf
• White dwarf
• Neutron star
• Black hole!
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White Dwarf
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Mass: bit less than the sun’s
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
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Neutron Star
• Mass: around 2 solar masses
• Size: about 10 km (city!)
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• Density: about 10 kg/m
(atom’s nucleus!)
• Made of: neutron gas
(degenerate)
• Made in: supernova explosions
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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
density—the singularity
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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)
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Black Holes
• Measure mass by visible orbiting
body (Newton’s version of Kepler’s
3rd)
• Most likely found in binary stars
(black hole + regular massive star)
• Are not cosmic vacuum cleaners
(but don’t get up close!)
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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 xrays (blackbody)
• Search in binary x-ray sources
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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)
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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
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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
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