Transcript Stellar Evolution Notes

Stellar Evolution
Structure
Mass governs a star’s temperature,
luminosity, and diameter
 Hydrostatic Equilibrium – the balance
between gravity squeezing inward and
pressure from nuclear fusion and radiation
pushing outward

Hydrostatic Equilibrium
Star Formation

Nebula
– a cloud of interstellar gas and dust where the
formation of a star begins, when it collapses
on itself due to its own gravity
Nebula
Protostar
a rotating disk shape with a hot
condensed object at the center formed
when the nebula cloud contracts
 The condensed object becomes a new star
 Fusion begins when the temperature
inside the star becomes hot enough

Protostar
Star
Our Sun’s Lifecycle (part 1)
Nebula
 Protostar
 Main sequence star

– Fusing Hydrogen into Helium
Expands into a Red Giant
 Outer layers are driven off
 Star contracts back to normal size

– Fusing Helium into Carbon
Our Sun’s Lifecycle (part 2)
A Sun size star will never be hot enough to fuse
carbon
 Outer layers are driven off forming a Planetary
Nebula
 Forms a White Dwarf about the size of Earth

– No longer nuclear
– Supported by resistance of electron being squeezed
together

Becomes a Black Dwarf when it runs out of
energy
Red Giant
Planetary Nebula
White Dwarf
Supergiant
Massive Star Lifecycles
Several Red Giant phases
 When the core of a massive star has
formed iron, no more reactions can occur,
and the core violently collapses in on itself
 Supernova

– a massive explosion that blows off the outer
portion around a neutron star
Supernova
Neutron Star

Forms quickly when the collapse of a
supernovae is halted due to the neutrons being
tightly squeezed together
– Extremely dense – 100 trillion times more dense than
water
– Very small – a radius of approx. only 10km
Neutron Star
Black Holes
Black Holes are formed by the most
massive stars (20 times the size if the
Sun)
 The collapse of the star continues forever
with gravity that is so immense the not
even light can escape it

Black Hole
http://www.youtube.com/watch?v=f_KLOFe2rDY