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

Ursa Major - Constellation

Big Dipper - Asterism

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

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