 How Stars Form: -The space around stars contains gas/dust  A nebula is a large cloud of dust/gas, some nebulas glow lit by other stars and some are cold and dark that block the light from distant stars behind it

 Stars are created by gravity.  Gravity pulls the nebula’s dust/gas into a denser cloud, as it contracts it heats up  A contracting cloud of dust with enough mass to form a star is called a proto-star  A star is formed when a contracting cloud of dust/gas becomes so dense and hot that nuclear fusion begins

 Spend about 90% of their lives in main sequence (converting hydrogen to helium)  A star’s mass determines the star’s place on the main sequence and how long it will stay there  The amount of gas/dust when the star forms determines the mass of the star

 High mass stars become the brightest/bluest, about 300,000 times brighter than sun  Because they are bigger and burn so brightly, they only last for a few million years  A yellow star like our sun will remain stable for 10 billion years  A red sequence star may stay in sequence for more than 100 billion years (Formed from small nebulas, 1/10 the sun’s mass)

 When a star runs out of fuel gravity starts to compress the core and causes it to shrink  Then the star will begin to fuse helium into carbon/oxygen/and other heavier elements  Once all fuel is gone it causes the star to die and turn into a white dwarf, neutron star, or black hole

 Can be 8 times as massive as the sun will eventually turn into white dwarfs  The dying star is surrounded by a glowing cloud of gas called a planetary nebula (Because the 1 st ones found looked like planets viewed through a small telescope)  Once it blows off most of its mass, only its hot core remains (Size of Earth but still about the same mass as before)  Once it cools its called a black dwarf (Takes 20 billion years so the universe has not been around long enough for this to occur)

 More than 8 times the mass of the sun, grow into super-giants creating new elements, the heaviest being iron  Dies quickly because it consumes its fuel very rapidly  Once the star runs out of fuel the star collapses and explodes as a supernova (Becomes brighter than an entire galaxy)  Produces elements heavier than iron -Rare Earth Elements -Uranium, Platinum, Gold, Etc

 The heavier elements in our solar system, including the atoms in your body, came from a supernova that occurred in our galaxy billions of years ago  As the supernova spews material into space, its core continues to collapse  If the remaining core has a mass less than 3 times the sun’s mass, it will become a neutron star (This star is dense, electrons/protons are crushed together by the enormous gravity to form neutrons)

 Neutron stars are much smaller and denser than white dwarfs  A spoonful of a neutron star would weigh nearly a billion tons on Earth  Can spin hundreds of times a second  If a neutron star gives off strong pulses of radio waves it is called a Pulsar

 If a star’s core after a supernova explosion is more than 3 times the sun’s mass, gravity causes the collapse beyond the neutron star stage  The pull of gravity increases and the speed required to escape the star’s core reaches the speed of light

 Beyond this point, nothing can escape and a black hole is formed  A black hole is an object whose surface gravity is so great that not even electromagnetic waves, traveling at the speed of light, can escape from it