2What is a Star? NUCLEAR FUSION A star is a hot ball of plasma (electrically charged gases, mainly hydrogen & some helium) that shines at its coreThe star shines due to a process called …NUCLEAR FUSIONThis 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!
3How 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.
5Life cycle of starsAll 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 massStars have 3 general mass categories:Small or low-mass starsMedium or medium-mass stars our sun is this!Large or high-mass stars
6Most of the stars in the Universe Low mass starsHave less mass than our SunCalled RED DWARFSUses 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 DWARFMost of the stars in the Universeare Red Dwarfs!
7Our Sun will become a Red Giant in about Medium mass starsHave mass comparable to our SunHydrogen is consumed faster over a period ofabout 10 billion yearsWhen the hydrogen is used up, the core slowly collapses raising the temperature inside the star & expanding the outer layersThe outer layers are cool and appear red RED GIANTEventually the layers disappear and it becomes a WHITE DWARFOur Sun will become a Red Giant in about5 billion years!
8high mass stars Have mass greater than our Sun Hydrogen is consumed over a period ofabout 7 billion yearsAs it uses up its hydrogen, it swells to become a red SUPER GIANTHigh mass stars always come to a violent end! The core collapses and the outer layers explode called a SUPERNOVAThe remaining inner core material packs tightly together forming a NEUTRON STARGases drift off to become NEBULAS (which will start the life cycle of a star once again)
9high mass stars (continued …) High mass stars that are extremely large (30 times the mass of the sun), end their life as a BLACK HOLEThe supernova explosion is so massive that gravity becomes a crushing force even light cannot escape a black hole’s gravity!
11The brightness of a star is referred to as luminosity Colour of starsThe colour of a star depends its temperature. The temperature ofa 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 glowSmall stars are the coolest and tend to have a reddish glowOur sun is somewhere in the middle and has a yellowish glowThe brightness of a star is referred to as luminosity