Transcript White Dwarf

White Dwarf
Collapse
• The core of a giant star collapses as helium fuses.
– Outer layers continue to expand
– Loses over half its mass
• The lost mass comes off in helium flash explosions.
core
outer layers
of gas
Planetary Nebulae
• Ejected gas from a star is
lit up by the shrinking
core.
– Round shape
– Glows with colors seen
from planets
• The gas is called a
planetary nebula.
– Not really part of a planet
Degenerate Matter
• After explosions the remaining core collapses due to
gravity.
– Radiation too weak
• At high density, the electromagnetic force between
electrons holds the material of the core apart.
• This compressed material is degenerate matter.
– Core of giant stars
– Sun mass in Earth size
Fate of the Sun
• The Sun will collapse after
millions of years as a
giant.
-20
-15
Abs. Magnitude
-10
– Heat to class A or B
– Shrink to Earth size
-5
0
5
Sun
10
15
20
O B A F G K M
Spectral Type
• The end of the sun will be
a small, hot star that will
last until the remaining
material burns up.
Bipolar Nebulae
• Planetary nebulae can
have multiple flashes.
– Ring of ejected matter
around the core
– Later flashes blocked by
ring
• The gas goes in the
remaining two directions
forming a dumbbell or
hourglass shape.
Bare Core
• Stars less than 8 M will
all end by helium flashes
as gas is ejected.
-20
-15
Abs. Magnitude
-10
-5
• The remaining core is
called a white dwarf.
0
5
10
15
20
O B A F G K M
Spectral Type
• The white dwarf will cool
over billions of years until
it is black.