A journey to the stars

What is a Star? NUCLEAR FUSION A star is a hot ball of plasma (electrically charged gases, mainly hydrogen & some helium) that shines at its core The star shines due to a process called … NUCLEAR FUSION This is a nuclear reaction where 2 or more atomic nuclei collide at very high speeds & fuse to form a new type of atom. This causes the release of an enormous amount of energy in the form of light!

How a star is born A new, forming star is called a PROTOSTAR Stars are born out of a vast cloud of dust & gas called a NEBULA. Inside the nebula, gravitational pull causes the atoms of the dust and gas to clump together and become dense. Over time, the center of the nebula becomes more and more dense and the tightly-packed atoms begin to heat up  this causes hydrogen to fuse into helium via nuclear fusion! At this point the star begins to shine, however its hot core remains surrounded by gas and dust. As the star shines, enormous energy is created which blows the nebula away.

Life cycle of stars All stars have a life! They go through the stages of birth, development, and finally death. How a star evolves in its lifetime depends on its original mass Stars have 3 general mass categories: Small or low-mass stars Medium or medium-mass stars  our sun is this! Large or high-mass stars

Most of the stars in the Universe Low mass stars Have less mass than our Sun Called RED DWARFS Uses nuclear fusion to produce energy for as long as 100 billion years! Hydrogen is consumed VERY SLOWLY! The star eventually cools to become a very faint WHITE DWARF Most of the stars in the Universe are Red Dwarfs!

Our Sun will become a Red Giant in about Medium mass stars Have mass comparable to our Sun Hydrogen is consumed faster over a period of about 10 billion years When the hydrogen is used up, the core slowly collapses raising the temperature inside the star & expanding the outer layers The outer layers are cool and appear red  RED GIANT Eventually the layers disappear and it becomes a WHITE DWARF Our Sun will become a Red Giant in about 5 billion years!

high mass stars Have mass greater than our Sun Hydrogen is consumed over a period of about 7 billion years As it uses up its hydrogen, it swells to become a red SUPER GIANT High mass stars always come to a violent end! The core collapses and the outer layers explode  called a SUPERNOVA The remaining inner core material packs tightly together forming a NEUTRON STAR Gases drift off to become NEBULAS (which will start the life cycle of a star once again)

high mass stars (continued …) High mass stars that are extremely large (30 times the mass of the sun), end their life as a BLACK HOLE The supernova explosion is so massive that gravity becomes a crushing force  even light cannot escape a black hole’s gravity!

The brightness of a star is referred to as luminosity Colour of stars The colour of a star depends its temperature. The temperature of a star, and therefore its colour, actually depends on the amount of mass it has. Very massive stars are the hottest and tend to have a bluish glow Small stars are the coolest and tend to have a reddish glow Our sun is somewhere in the middle and has a yellowish glow The brightness of a star is referred to as luminosity