Stellar+Evolution+Group+One+Michael+A+and+Vanessa+C

=__**Stellar Evolution!**__=

Earth Science - Orange Class


= = =__**What type of stars are there in our Universe?**__=

There are many different types of stars. Stars are categorized by: - Their luminosity - The intensity of their heat and the shorter the life span
 * Their color and their age.
 * This determines:
 * The hottest and brightest type of stars are blue or white.
 * The second hottest and brightest type of stars are yellow.
 * The coolest and dimmest type of stars are red.
 * The larger the mass of the star, the less luminosity and heat it has



-One star that we can observe and analyze is the red giant in the top right hand corner. It is much cooler than the other stars, but being so big it makes it fairly bright in luminosity. It also has a absolute magnitude of around -10.
 * Example of the how diagram works:

= = =__Red Giants__=


 * Although red stars are the coolest and dimmest they are great in size.
 * This allows them to be more visible at times than blue or white stars from Earth
 * These type of stars are called red giants: Aldebaran, Arcturus
 * Even larger types of stars are called red super giants: Rigel, Canopus
 * The largest stars are red super giants: Antares, Betelgeuse



= = =__Variable Stars and Pulsars__= = = -Contractions increases temperature and luminosity -Expansion decreases temperature and luminosity -Example Of pulsating stars are Cepheids -Cepheids are yellow super giants whose period of brightness lasts about 5 days
 * The brightness of stars goes through periods of change
 * Pulsating Stars change luminosity when they contract and expand:
 * Pulsars are stars that emit light and radio waves
 * Neutron stars are left behind by supernovas



=__Creation of Stars__=

and they begin to come together - Called protostars that a reaction takes place -Marks the change from protostar to an actual star balance each other and the star stops contracting
 * Large low-density clouds of dust and gas exist between stars in space
 * Clouds form after the explosion of a star
 * Clouds are called nebulae and average 25 light-years in diameter
 * Nebulae is 99% gas (mostly hydrogen) and 1% of tiny grains of dust
 * Force from outside begins to condense the material within the cloud
 * Force leads to an attraction of gravity between the dust and gas
 * Particles move closer and the temperature increases and starts to glow:
 * The temperature continues to rise and soon the center becomes so hot
 * Light hydrogen nuclei combine and form heavy hydrogen nuclei:
 * Star reaches a stable state when an amount of energy and force of gravity
 * Big stars appear blue and white when they are in their stable state
 * Smaller stars take longer to reach stable state and appear more yellow-orange



=__Creation of the Red Giant__=

maintaining the same diameter and radiation consistently does not balance the force of gravity
 * The stable state is the time period in when stars lives most of its life time
 * At some point, they core only has so much light nuclei that energy/fusion
 * The core starts to contract
 * Reaching a temperature so hot, the core allows the outer layer to expand
 * This increases the star's surface area, raditiation of light, and lumonousity
 * It reaches to such a degree that it then is known as a red giant or super giant



=__Creation of the White Dwarfs__=

and no longer supports the outer layer of the star
 * When the energy or fuel of the core runs out, the core changes in temperature and pressure
 * As a result of this the star collapses within itself very tightly becoming around the same size as Earth
 * No more fuel = decrease in temperature and luminosity
 * The sun will eventually become a white dwarf in around five billion years, but is still in its stable stage



=__Supernovas!__=

that it becomes a black dwarf becoming a spectacular show in the sky!
 * As the star becomes older in its life as a white dwarf it will become so tight
 * The black dwarf becomes so tight that even the core itself starts to collapse
 * The temperature rises dramatically to a point where the star is ready to burst
 * The explosion is so violent that, that one star outshines the rest for a few weeks




 * I hope that this study guide to a stellar evolution will help you do well on the final exam!

__Bibliography__

 * Earth Science text book: Chapter 21
 * Chapter 21 - Stars and Galaxies
 * The Pleiads Science lab
 * "The Life of a Star" flip book

= =