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Stellar Evolution
Clouds of gas and
dust are floating
around in space
These are called
“nebula”
Horsehead Nebula
Crab Nebula
Omega Nebula
Gravity causes this
gas and dust to
contract
As the gas and dust falls in on itself,
it creates a stronger gravitational
field and heats up.
Making “protostars”
As more and more
gas and dust fall
into the protostar,
the gravity gets
stronger and
stronger, causing
intense heat and
pressure in the core
Nuclear fusion starts
The protostar becomes a star
How long a star “lives”, with fusion
powering it’s core depends on how
massive it is.
A star like the Sun will “live” about
10 billion years. The Sun is currently
about 5 billion years old.
Bigger stars burn brighter, but
burn-out faster
The Death of Stars
Red Dwarf: The smallest, dimmest stars,
less than .4 solar masses. Longest lasting
stars. Most stars are red dwarves. They
use fusion to slowly combine hydrogen
into helium. They would take about 2
billion years to contract to the main
sequence and 6 trillion years to use up all
its hydrogen, after which fusion would
shut down, and the star would grow cold
and dark.
Sunlike stars: With a mass between .4 and 4
solar masses, use fusion to combine
hydrogen into helium.When they run out of
hydrogen (6 trillion to 310 million years), the
outer layers of the star expand into a “red
giant” while the core contracts and starts to
fuse helium into carbon and oxygen. The
core cannot get hot enough to fuse carbon
and oxygen, so when the helium runs out,
fusion stops. The outer layers of the star are
blown off, and you are left with a “white
dwarf” which slowly cools off and grows
dim, becoming a brown dwarf.
“Big” stars over 4 solar masses can use fusion
to create energy up to iron. After iron, fusion
reactions don’t produce energy. With no energy
pushing outward from the core, gravity causes
the star to quickly collapse and then explode in
a supernova. Big stars may live as short as 7
million years up to 310 million.
“Big” stars (between 4 and 15 solar masses)
that supernova produce a neutron star. All that
mass would be squished down to a tiny size
from the enormous gravity, becoming very
dense. 1 cm3 of it would weigh 10 million
tons. Spinning neutron stars are called
pulsars.
X-ray source
Neutron stars are about 12 miles wide and when
they spin extremely fast they can develop strong
magnetic fields and are called Magnetars.
The magnetism occasionally rips the solid crust
of a Magnetar apart, releasing more energy in .2
seconds than the Sun puts out in 250,000 years.
The magnetism would kill you within 600 miles
by reshaping the atoms in your body.
“Huge” stars with more than 15 solar masses last less
than 7 million years and contract with so much
gravitational acceleration, that no physical force in
the Universe can stop the collapse. These stars
become “black holes”. Nothing that comes near it can
escape its gravity, not even light.
How stars die….
Small stars
turn off after trillions of years
Average stars
become Red Giant then white dwarf
Big Stars
explode and leave a neutron star
Huge stars
explode and leave a black hole