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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