Life Cycle of Stars
New Solar System
Life Cycle of Stars
Fetus (Stellar Nebula Stage)
• Nebulae are huge
clouds of gas and dust
(singular: nebula)
• Stars form in nebulae
by the force of gravity
• Nebular gas and dust
are from an exploded
star.
Fetus -- Proto-Star Stage
• Hydrogen and
helium are the main
gases in stars.
• The proto-star
begins to spin and
glow - temperature
increases.
Birth - Maturity of Stars --
Main Sequence Stage
• Fusion occurs – hydrogen atoms are fused into helium, giving off tremendous energy.
• The force of gravity is in equilibrium (balanced) with the energy from fusion.
• Most stars will spend 90% of their life cycle as main sequence stars
Maturity - Main Sequence
Hot, Bright
Hot, Dim
Cool, Bright
Cool, Dim
Maturity - Main Sequence
• Hertzsprung-Russell (H-R) Diagram
plots the surface temperature of stars
against their luminosity
– Luminosity = the total amount of energy a
star gives off each second
– Hottest stars are brightest
– Coolest stars are dimmest
– Most stars reside in the main sequence
• A diagonal pattern from lower right to upper left
H – R Diagram
Where would
dying stars plot
on the diagram?
Point A
Point B
Where would
stable stars plot
on the diagram?
Point C
Where would
dead stars plot
on the diagram?
Mid-life Crisis -- Red Giant / Red Supergiant Stage
• Hydrogen in the core is
used up
• The star fuses heavier
elements, like carbon.
• Star becomes unstable
as the forces of fusion
and gravity are no
longer equal.
• Cooler in temperature.
Hydrogen-to-helium fusion stops
Old Age -- Supernova and Planetary Nebula
• Massive Stars go Supernova:
• Helium is fused into Iron
• Sun-like stars become
Planetary nebulae:
• Fusion of elements up to
carbon occurs in the core.
• Outer layers lift off
Death : Average Stars --
White Dwarf Stage
Average Sun-Sized Stars
• All fuel is used up.
• Red Giant collapses into a
white dwarf as gravity wins
over fusion.
• Dim, faint star with high
temperature.
• Sun-like star becomes white
dwarf made of carbon.
• Black Dwarf – no energy –
cools – turns black
A diamond weighing 10
billion trillion trillion carats
is at the heart of a dead
white dwarf star
nicknamed Lucy.
It’s 50 ly from us, in the
constellation Centaurus.
Death: Massive Stars -- Supernova Stage
• Massive stars, much larger than our sun,
have a different life cycle.
• Giants and super giants will explode as a supernova.
• Some massive stars collapse to form black-holes or become a neutron star.
• Black holes occur with VERY massive stars – Strong gravity, all matter trapped
• Neutron stars – all elements join – Removing all space, making incredibly dense
star
The Milky Way…look alike
Closest
Galaxy
to us?
Milky
Way
Hubble Space Telescope
Named after Edwin Hubble
Pictures of Supernovae
Hubble Photos
Visible Light
Infrared Light
Stars can be grouped into
Constellations.
• Ancient civilizations never grouped planets
with stars because planets are constantly in
motion, whereas stars are in a fixed position
and pattern.
Polaris – the North Star
Andromeda Galaxy