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 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
A mass in the middle grows larger as it spins, pulls in more dust and gas, and heats up
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