Transcript Death of Low Mass Stars 8 Solar Masses or less

Death of Low Mass Stars
8 Solar Masses or less
• All stars become a red giant.
All stars will live to be a Red
Giant, then…
• In the core of the Red Giant He is fusing
into C.
• MAJOR Problem!!! Core temps need to
reach at least 600 million K for C to ignite
into heavier elements (mainly O). Low mass
stars cannot do this.
• Creation of a Planetary Nebula
Planetary Nebula
• The shell of the star (red giant outer surface) is
subject to a series of explosions that eject gas
and dust into space (nebula).
• A star can lose up to 1/2 the original mass.
• Diameter can be very large (typically 1 ly)
• Gas expands 30 km/s
• Usually circular in shape
• Gas and dust in nebula becomes part of the
interstellar medium (ISM). Makes future
stars!!!
Ring Nebula (M57)
found in Lyra
Ring Nebula again… Hubble
White Dwarf
• As the surface of the Red Giant expands
away, the core is exposed, the White Dwarf.
• Extremely small, dense and hot. About the
size of Earth with a density of 1010 kg/m3
(an object with the volume of 1 grape would
have a mass of 1 ton… that’s like the mass
of an elephant!!!).
• Shines from stored heat, no fusion occurs in
the core… the star is officially dead :(
• Usually, but not always, seen in the center
of planetary nebulae.
White Dwarf compared to the
Sun/Earth
Cat’s Eye Nebula (NGC 6543)
found in Draco
White Dwarf
Planetary Nebula
• A white dwarf is a whitish
dead star having low
luminosity, small size and
very great density.
These white dwarf
stars are intensely hot
... but they are
cooling. Their interior
nuclear fires no longer
burn, so they
will continue to cool
until they fade away.
The white dwarfs are circled.
Helix Nebula
• Here’s
another
one!!!!
Black Dwarf Stars
• Cooled remains of a white dwarf.
• The resistance of electrons from being
squeezed together (electromagnetic
repulsion) keeps gravity from compressing
it further. Called Electron Degeneracy
• The black dwarf will continue to exist at
temps close to absolute zero forever….
What is a Nova explosion?
• A star suddenly increasing in brightness,
typically by 10,000 times.
• Caused by an explosion on the surface of a
very hot star.
• Unlike a supernova, a nova explosion does
not destroy the star.
Can a low mass star, like the Sun,
have a NOVA explosion?
• Yes, but usually if it is part of a binary star
system.
• Binary Star System- 2 or more stars in
orbit about each other held together by their
mutual gravitation. MOST “stars” are
binary systems. Our closest star is a 3 star
system (centauri system).
Accreting White Dwarf
Still answering the question…
• One star must be a white dwarf, the other
has recently become a red giant.
• The white dwarf will steal some of the
expelled matter. Once it reaches the
tremendously hot surface it ignites causing
a flash.
Nova Explosion in Binary
System
What is a Supernova?
• When a large mass
star (8 solar masses
or more)
EXPLODES
destroying the star.
Unlike a Nova that
does NOT destroy
the star
• Brightest/most
energetic event in
the Universe (2nd
only to the Big
Bang).
• YES!!! ONLY
if it’s part of a
Binary System.
• If a white dwarf
star has
accreted more
than 1.5 solar
masses, then
electron
degeneracy
cannot stop
gravitational
collapse.
• Called a Type I
Supernova
Can a small mass star, like the
Sun have a supernova explosion?
Type I SN