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Star lifecycle
Star Lifecycle
Some background Knowledge:
Nuclear fusion - combining smaller
elements into larger elements. Leftover
mass is converted into energy. (Done best
in stars only)
Nuclear fission - splitting larger elements
into smaller elements with the release of
energy in the process. (Done in nuclear
power plants here on Earth)
Star Lifecycle
What is a star?
 A star is a really hot ball of gas, with
hydrogen fusing into helium at its core.
 Stars produce light energy, heat energy,
and electromagnetic waves.
 Stars spend the majority of their lives
fusing hydrogen, and when the hydrogen
fuel is gone, stars fuse helium into carbon.
 The more massive stars can fuse carbon
into even heavier elements like Iron (Fe).
Star lifecycle
A nebula is a cloud of dust and gas,
composed primarily of hydrogen (97%) and
helium (3%).
Within a nebula, there are varying regions
when gravity causes this dust and gas to
“clump” together.
Star Lifecycle
As these “clumps” gather more atoms
(mass), their gravitational attraction to
other atoms increases, pulling more
atoms into the “clump.”
All stars begin as Nebulae
Gravity pulls a nebula together into a
protostar (If it has enough mass)
Star Lifecycle
 A star is officially born when
nuclear fusion starts
If a star doesn’t have enough mass
to start nuclear fusion, it becomes a
brown dwarf.
Star lifecycle
Stars life spans depend on their mass
Stars with less mass actually live longer because
they burn slower.
Massive and super massive stars live fast and
hard and die young.
Our sun is 4.6 billion years old. Currently
halfway through its lifespan.
Stars spend the majority of their
lives fusing Hydrogen into Helium
(the main-sequence stage)
Star lifecycle
• When the hydrogen fuel is gone, stars
fuse Helium into Carbon.
• The more massive stars can fuse carbon
into even heavier elements.
• Iron (Fe)is generally the largest element
being fused in stars.
• Larger elements than Fe are usually
produced via supernovas
Star Lifecycle
Star Lifecycle
• When a star has finished it’s main sequence
and begins to die:
Death of Stars:
After a star runs out of fuel, it becomes a
white dwarf, a neutron star, or a black hole.
Low to medium mass stars:
Star ---> red giant ---> planetary nebula --->
white dwarf ---> black dwarf
Star lifecycle
Star lifecycle
High Mass Stars:
Star ---> supergiant ---> supernova --->
neutron star or black hole (most massive
stars)
Pulsars – Spinning neutron stars that give
off pulses of radio sources. Left over from
super massive star supernovas.
Black Holes – From the most massive stars
(More than 40 times bigger than our sun).
 Nothing can escape the gravity of a black
hole, not even light.
Star Lifecycle
Star lifecycle
Our sun: (An average Joe type of star)
About half way through it’s life.
We can calculate an approximate
mass and rate at which it is burning
fuel (fusion Hydrogen to Helium).
From those numbers we can make a
good estimate of just how long the
sun has left before it goes Red Giant
to white dwarf finishing as a black
dwarf eventually.