Download Stars - winterk

The “Life & Death” of Stars
Let’s review: What is a star?
• Giant ball of hot gases
• The huge objects in
the universe
• Our Sun is an example
of a star
• Made of mainly
hydrogen and some
helium
How do stars generate energy?
• Stars burn by a process called nuclear
fusion
• This process combines two hydrogen atoms
into one helium atom, which then fuse to
form elements with even more protons
• This process gives off a lot of heat & energy
• Gives the illusion of “burning”
Types of stars
• 3 main sizes of stars
• Small/medium (like our Sun)
• Large (aka giant)
• Very large (aka supergiant or hypergiant)
• Different colours of stars indicate they’re different temperatures
• Blue is hottest
• Yellow is average
• Red is ‘coolest’
• Usually, the bigger the star, the cooler it is
• Most big stars are called Red Giants because they’re relatively cool
• Blue giants are very rare
• The hotter the star, the shorter its lifespan
Sizes of stars
1) small / med – most common
2) large – rare
3) extremely large – very rare
• The Sun is a med (average) sized
star
• Small stars are called dwarf stars
• Large stars are called Giants
• Extremely large stars are called
Supergiants or Hypergiants
The “Birth” of a Star
• All stars start out the same
•
•
•
•
way, as a nebula
A nebula is a giant cloud of
gas and dust
Stars are created in a nebula
as the gases contract due to
the force of gravity, turning
into a hot, dense clump
As they become larger, they
heat up until they reach a
temperature of 10 000 000 C
At this temperature, nuclear
fusion begins
A Star’s “Life”
• For the major part of a star’s “life”,
•
•
•
•
it undergoes nuclear fusion
Lower-mass stars can undergo this
process for up to 100 BILLION
years!
Stars like the Sun can last for about
10 billion years
Higher-mass stars produce energy
for only a few million years
Fast-burning, hot (blue) stars only
last for a million years… yikes!
A Star’s “Death” 
• A Star begins to “die” when the
hydrogen that fuels it runs out
• H has fused into new substances (He)
• Outer layers swell
• Once the core fuses into lead, fusion
stops and the star collapses inward,
followed by an outward projection of
particles
• Depending of the star’s size, its
collapse is either in the form of a
planetary nebula or a supernova
• After that, it then becomes one of the
following:
1) White dwarf (small/medium-sized stars)
2) Neutron star (large stars)
3) Black hole (extremely large stars)
Supernovas
• In 1987, Canadian astronomer
Ian Shelton discovered one
while working at an observatory
in Chile
• His discovery was by accident!
• He was looking at images of
stars when he noticed something
unusual: one star looked MUCH
brighter than the others
• Named it SN 1987A and it is
163 000 light years away
• This means Shelton was looking at the
supernova the way it was 163 000 yrs
ago!
• SN 1987A was the closest one
to Earth since 1604
White Dwarfs
Life After Death of Small & Medium Stars
• When the star’s core
becomes lead it can
not undergo fusion
any longer
• This white hot ball of
lead is called a white
dwarf
• It cools over a loooong
time to form a black
dwarf star
Neutron Stars
Life after death of a large star
• Sometimes a star is so heavy
& under so much pressure
that it cannot support its
weight (even if it’s fused into
lead!)
• The atoms collapse even
further creating a ball of
neutrons
• This forms a rapidly spinning
neutron star that is only a few
kilometers in size
• We see neutron stars from the
radiation that shoots out of
either end
Black holes
The Life After Death of Huge Stars
• Sometimes a star is so heavy
•
•
•
•
•
that not even the neutrons can
stay apart
The neutrons crash together,
forming a black hole
After that we are not sure as
this creates a black hole
A black hole is an object so
dense that not even light can
escape it
We can find black holes by
looking for objects in space that
are orbiting seemingly empty
space
These are very, very rare
How will our Sun “die”?
Nuclear fusion
Death of a Biiiig Star
Nuclear fusion
Supernova
Black hole
Nebula
“Life” Sequence of Stars
Star’s Size
Small/Medium
Large
Phases of a star’s “life & death”
nebula  nuclear fusion  red giant 
planetary nebula  white dwarf 
black dwarf
nebula  nuclear fusion  red
supergiant  supernova  neutron star
nebula  nuclear fusion  red
Extremely Large
supergiant  supernova  black hole
Life cycle of Stars… in pictures