Transcript Life Cycles of Stars

Life Cycles of Stars
Stars
• Stars are a large hot balls of plasma that
shine
• The Sun is the Star in our solar system
• A group of stars that form a recognizable
shape are called constellations
• A smaller group of stars with a
recognizable shape within a constellation
are called asterisms
Stars
Big Dipper - Asterism
Ursa Major - Constellation
A Star is born...
Stars are Born From NEBULAS
• NEBULA – a cloud of dust and gases,
that eventually collapse to form a star.
• The gravitational pull from a nearby
star OR the shockwave from an
exploding star can trigger the collapse
of a nebula
A Collapsing Nebula
Dust and gases are pulled in by
gravity to form larger masses
A Collapsing Nebula
A mass in the middle grows larger as it spins,
pulls in more dust and gas, and heats up
A Collapsing Nebula
A protostar has formed
Life Cycle of Stars
Size Matters
• Different size stars go through similar life
cycles, however they are different:
1) Low Mass Stars
2) Medium Mass Stars
3) High Mass Stars
All begin as
nebulae that
collapse to
form protostars
Low Mass Star
• Burns slowly and lasts for 100 billion years
• Mature into a red dwarf (most stars in the
universe are red dwarfs)
• When the fuel for nuclear fusion runs out,
a red dwarf cools into a white dwarf
Medium Mass Star
• Last for about 10 billion years
• When a medium mass star runs out of
fuel, it collapses under its own gravity
• The collapse heats up and pressure
increases
• Star expands and becomes a Red Giant
• Eventually, burns out to form a white
dwarf
High Mass Star
• Lasts up to 7 billion years (usually less)
• At least 10 times the size of our Sun
• When a high mass star runs out of fuel it
collapses and expands to form a Supergiant
• Supergiants end in a massive explosion called
a supernova
• End result: 1) cosmic debris - nebula
2) a neutron star (or pulsar)
3) a black hole
Supernova
• Supergiants that run out of fuel end in a
massive explosion
• Many nuclear fusion reactions occur and
new elements form and explode into
space
• The debris from the explosion is the
source for a new nebula
• What remains of the star depends on
the original size of the star
Neutron Star
• Remaining core of a supergiant that was
less than 40 times the size of our Sun
• Also called a pulsar
• Very dense matter made of neutrons
Black Hole
• Remaining core of a supergiant that was
more than 40 times the size of our Sun
• The core of the supergiant, after a
supernova, is so dense that its
gravitational pull sucks in space, time,
light and matter
• Thought to be at the centre of all galaxies
Summary
• All stars are born from a nebula
• Nebulae collapses and pulls in dust and gases to
form a protostar
• Depending on the size of the star that forms, a
different fate is met
• Low and medium mass stars burn out to become
white dwarfs
• High mass stars burn out in an amazing explosion
called a supernova, which gives birth to a new
nebula
Questions
• page 305: #2 – 5, 11